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Restoration of endodontically treated immature teeth : influence of post fit on bonding properties of… Berthold, Christine 2015

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RESTORATION OF ENDODONTICALLY TREATED IMMATURE TEETH – INFLUENCE OF POST FIT ON BONDING PROPERTIES OF CONVENTIONALLY AND ADHESIVELY LUTED FIBER-REINFORCED COMPOSITE POSTS  by Christine Berthold  DDS, The Martin-Luther University Halle-Wittenberg, Germany, 1997 Dr. med. dent., The Martin-Luther University Halle-Wittenberg, Germany, 2002 Priv.-Doz., The Friedrich-Alexander University Erlangen-Nuremberg, Germany, 2012  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR  MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Craniofacial Science)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) June 2015    © Christine Berthold, 2015 ii  Abstract Objective: To evaluate the influence of post fit and luting system on pull-out force and failure mode of conventionally and adhesively luted fiber-reinforced composite posts (FRCP). Methods: 260 extracted bovine deciduous teeth were randomly assigned to each of the four luting systems (Fuji Plus (FP), RelyX Unicem (RXU), Multilink Primer/Multilink (MLP_ML), LuxaBond/LuxaCore Z (LB_LCZ and three post fits (Congruency (C), medium incongruency (MIC), high incongruency (HIC)) (n=20/group). The teeth were decapitated, root canal treated, embedded and post space was prepared. The FRCPs (Macro-Lock Post sizes 1, 3 and 6) were pretreated and inserted, according to the manufacturer’s instructions. The custom-made titanium-post was inserted with Ketac Cem (control) (n=20).  After water storage (24h, 37°C), pull-out test was performed. The data were analyzed using Kolmogorov-Smirnov test (p>0.05), Two-way ANOVA and post-hoc tests (Dunnett T3 with Bonferroni correction) (α=0.05). Failure mode was assessed using a stereomicroscope. Results: The influence of post fit and luting system was statistically significant (p<0.001), while the interaction of the two factors was not (p = 0.030). When comparing pull-out forces for the three post fits, significant differences (p < 0.017) were found between C (436.6±148.7 N) and MIC (426.0±102.1 N) and C and HIC (397.5±89.8 N). Failure mode was dominated by failure between dentin and luting system (64.2-70.7%) and between luting system and post (29.3-35.5%), for all post fit groups. iii  Pairwise comparison revealed significant differences in pull-out force (p < 0.008) for all luting systems (FP: 441.2±44.9 N, RXU: 390.7±80.5 N, MLP_ML: 379.3±106.8 N, LB_LCZ: 544.0±96.6 N), except when comparing RXU and MLP_ML. Pull-out forces, achieved with all luting systems, were significantly higher compared to the control (211.2±35.1 N). The main failure for FP was found between luting system and post (92.3%) while main failure for RXU (99.5%), MLP_ML (95.8%), LB_LCZ (65.5%) was found between dentin and luting system. Conclusion: Post fit and luting system influenced the pull-out force of conventionally and adhesively luted FRCPs. Congruent post fit achieved the highest pull-out forces. The three-step Etch & Rinse adhesive luting system LB_LCZ generated considerably higher pull-out forces than all other tested luting systems.  iv  Preface The present study is part of a comprehensive project with the aim to propose restorative guidelines for endodontically treated immature teeth. The project was started at the Friedrich-Alexander-University Erlangen-Nürnberg, Germany, with the author Dr. Christine Berthold as project leader. The present study is a result of collaborative work between the University of British Columbia (UBC), Canada, Department of Endodontics and the Friedrich-Alexander-University (FAU) Erlangen-Nuremberg, Germany, Dental Clinic 1 – Operative Dentistry and Periodontology. The study is submitted in partial fulfillment of the requirements for the combined MSc and diploma in Endodontics. The study is supervised by Dr. Markus Haapasalo and supported by the members of the research committee Dr. Ya Shen, Dr. Rick Carvalho and Dr. Caroline Nguyen at UBC. The experiments for this study were conducted at the Biomaterial Research Laboratory of the Dental Clinic 1 at the FAU Erlangen-Nuremberg. The rules and regulations of the FAU, for safe and ethical conduct of research, applied and were followed. According to the information, obtained from the Ethics Board at FAU and Animal Care at UBC, ethical approval was not required for this specific study on extracted bovine teeth. The analysis of the data and the writing of the thesis were accomplished at UBC. The findings of the study have not yet been published nor presented outside of UBC, however publication is in preparation.  v  The following table (Table 1, p. v) is an overview on the relative contribution of the author Dr. Christine Berthold and the co-workers for the present study.  Table 1. Overview of the percentage contribution of the author (Dr. Christine Berthold) and co-workers during the conduction, analysis and presentation of the study.  Procedure Contribution Author Contribution Co-workers (%) Study design and development of methodology 90% Dr. M. Haapasalo (10%) Acquisition of material support 100% None Acquisition of financial support 95% Dr. M. Haapasalo (5%) Planning and coordination of the experiments 100% None Extraction and cleaning of bovine teeth  50% Dr. S. Binus, Dr. A. Koch, Dr. B. Mitterhuber, Dr. C. Witte (50%) Manufacturing of the sample holders and jigs 20% H. Löw (80%) Sample slice and counterpart preparation 50% Dr. S. Binus, Dr. B. Holzschuh, Dr. A. Koch, Dr. P. Krug, S. Sney (50%) Post insertion 100% None Pull-out sample preparation 80% Dr. S. Binus, Dr. A. Koch (20%) Pull-out test 50% Dr. S. Binus, Dr. A. Koch (50%) Sample preparation for failure mode analysis 100% None Failure mode analysis 90% Dr. B. Mitterhuber, Dr. C. Witte, Dr. B. Holzschuh (10%) Data organization in SPSS 80% Dr. B. Holzschuh (20%) Statistical analysis and interpretation of the results 90% Dr. J. Aleksejuniene (10%) Illustrations 100% None Thesis writing and support 80% Dr. M. Haapasalo, Dr. R. Carvalho, Dr. Y. Shen, Dr. C. Nguyen, Dr. D. Ruse, Dr. Aleksejuniene (20%) Research reports 100% None   vi  Table of Contents Abstract .......................................................................................................................... ii Preface .......................................................................................................................... iv Table of Contents ......................................................................................................... vi List of Tables ................................................................................................................. x List of Figures ............................................................................................................. xiv List of Abbreviations and Symbols ........................................................................ xviii Acknowledgements .................................................................................................... xxi Dedication ................................................................................................................. xxiii Chapter 1: Introduction ................................................................................................... 1 Chapter 2: Literature Review .......................................................................................... 3 2.1  Endodontic Treatment in Immature Teeth ....................................................... 3 2.1.1  Teeth with Vital Pulp ................................................................................. 7 2.1.2  Teeth with Pulp Necrosis ........................................................................ 11 2.1.3  Complications after Completed Endodontic Treatment ........................... 19 2.1.3.1  Periapical Pathosis ........................................................................... 19 2.1.3.1.1  Periapical Pathosis Caused by Microorganisms ........................ 19 2.1.3.1.2  Periapical Pathosis of Non-microbial Nature .............................. 21 2.1.3.2  Fractures .......................................................................................... 22 2.1.3.2.1  Vertical Root Fractures .............................................................. 22 2.1.3.2.2  Cervical Horizontal or Oblique Fractures ................................... 23 2.2  Post-endodontic Restoration ......................................................................... 25 2.2.1  Reinforcement of Endodontically Treated Immature Teeth ..................... 27 vii  2.2.1.1  Bioceramic Cements ........................................................................ 29 2.2.1.2  Resin Composite .............................................................................. 30 2.2.1.3  Fiber-reinforced Composite Materials ............................................... 32 2.2.1.4  Posts ................................................................................................ 35 2.2.1.4.1  Fabrication ................................................................................. 37 2.2.1.4.2  Material ...................................................................................... 39 2.2.1.4.3  Design ........................................................................................ 40 2.2.1.4.4  Surface Conditioning .................................................................. 40 2.2.1.5  Luting systems .................................................................................. 41 2.2.1.5.1  Conventional Luting Systems ..................................................... 42 2.2.1.5.2  Adhesive Luting Systems ........................................................... 42 2.2.2  Luting of Posts to the Root Canal System ............................................... 44 2.2.2.1  Factors Influencing the Bonding Properties of Root Canal Posts ..... 44 2.2.2.2  In vivo evaluation of the Bonding Properties of Root Canal Posts .... 46 2.2.2.3  In vitro evaluation of the Bonding Properties of Root Canal Posts ... 48 2.2.2.3.1  Interface ..................................................................................... 48 2.2.2.3.2  Dentin Substrate ........................................................................ 50 2.2.2.3.3  Storage of Teeth ........................................................................ 52 2.2.2.3.4  Methods ..................................................................................... 53 Chapter 3: Aim, Research Questions and Hypotheses ................................................ 61 3.1  Aim ................................................................................................................ 61 3.2  Research Questions ...................................................................................... 61 3.3  Hypotheses .................................................................................................... 62 viii  Chapter 4: Materials and Methods ............................................................................... 63 4.1  Materials ........................................................................................................ 63 4.1.1  Substrate ................................................................................................. 63 4.1.2  Post Systems .......................................................................................... 63 4.1.3  Luting Systems ........................................................................................ 65 4.2  Methods ......................................................................................................... 69 4.2.1  Sample Preparation and Randomization ................................................. 70 4.2.1.1  Tooth Preparation ............................................................................. 70 4.2.1.2  Embedding of the Roots ................................................................... 71 4.2.1.3  Preparation of the Sample Slices and Counterparts ......................... 74 4.2.1.4  Group Distribution and Randomization ............................................. 78 4.2.1.5  Post Cavity Preparation .................................................................... 80 4.2.1.6  Post Insertion .................................................................................... 82 4.2.1.7  Preparation of the Post-Tooth Sample for Pull-out Testing .............. 86 4.2.2  Pull-out Testing ....................................................................................... 89 4.2.3  Failure Mode Analysis ............................................................................. 91 4.2.4  Statistical Analysis .................................................................................. 93 Chapter 5: Results ........................................................................................................ 95 5.1  Influencing Factors ........................................................................................ 95 5.1.1  Test for Preconditions for Two-way ANOVA ........................................... 95 5.1.1.1  Test for Normal Distribution of the Pull-out Force Data .................... 95 5.1.1.2  Test for Equality of Variances of the Pull-out Force Data ................. 95 5.1.2  Test for General Significance of the Influencing Factors ......................... 95 ix  5.1.2.1  Influencing Factor Post Fit ................................................................ 96 5.1.2.2  Influencing Factor Luting System ..................................................... 98 5.1.2.3  Combination of Influencing Factors Post Fit and Luting System ..... 103 Chapter 6: Discussion ................................................................................................ 107 6.1  Methodological Factors ................................................................................ 107 6.1.1  Dentin Substrate Selection and Storage ............................................... 107 6.1.2  Reinforcement and Luting Materials ...................................................... 109 6.1.2.1  Posts .............................................................................................. 109 6.1.2.2  Luting Systems ............................................................................... 110 6.1.3  Evaluation of Bonding Properties .......................................................... 111 6.1.3.1  Sample Preparation and Testing Procedure ................................... 112 6.1.3.2  Failure Mode Analysis .................................................................... 114 6.1.4  Study Limitations ................................................................................... 115 6.2  Results ......................................................................................................... 118 6.2.1  Dislodgement Forces and Failure Mode ............................................... 118 6.2.1.1  Post Fit as an Influencing Factor .................................................... 118 6.2.1.2  Luting System as an Influencing Factor .......................................... 123 6.2.1.3  Post Fit within the Luting System Groups as an Influencing Factor 131 Chapter 7: Conclusion ................................................................................................ 139 Bibliography .............................................................................................................. 142 Appendices ................................................................................................................ 209 Appendix A – Tables ..................................................................................................... 209  x  List of Tables Table 1. Overview of the percentage contribution of the author (Dr. Christine Berthold) and co-workers during the conduction, analysis and presentation of the study. ................................................................................................... v Table 2. Fractue load (N) of mature and simulated immature teeth, reinforced with different techniques and materials ............................................................... 35 Table 3. Comparison of different structural and bonding properties of human and bovine coronal dentin, based on the availabe literature. ............................. 51 Table 4. Overview of studies on bonding properties of FRC-posts, using at least two of the presently investigated luting systems. ............................................. 134 Table 5. Overview of bond strength and dislodgement force ranges for FRC-posts, luted with Fuji Plus, RelyX Unicem, Multilink Primer/Multilink or LuxaBond/LuxaCore Z, achieved in different studies ................................ 136 Table 6. Characterization of the different adhesive luting system types (ALST) by procedureal steps for conditioning, bonding and luting. ............................ 209 Table 7. Material specific data (manufacturer’s information) for Macro-LockTM Post Illusion X-RO (sizes 1, 3 and 6) (RTD, Saint-Égrève, France) .................. 210 Table 8. Material specific data (manufacturer’s information) for RPR Prototype Titanium Post (NTI GmbH, Kahla, Germany) ............................................ 210 Table 9. Material specific data (manufacturer’s information) for KetacTM Cem Aplicap (3M ESPE, Seefeld, Germany) .................................................................. 211 Table 10. Material specific data (manufacturer’s information) for Fuji PlusTM Capsule (GC Europe, Leuven, Belgium) ................................................................. 211 xi  Table 11. Material specific data (manufacturer’s information) for RelyXTM Unicem A2 (3M ESPE, Seefeld, Germany) ................................................................ 211 Table 12. Material specific data (manufacturere’s information) Multilink® Automix und Multilink® Primer A/B Light (Ivoclar Vivadent, Schaan, Liechtenstein) ..... 212 Table 13. Material specific data (manufacturere’s information) Etching Gel, LuxaBond® Pre-Bond, LuxaBond® Bond A/B und LuxaCore® Z  (DMG, Hamburg, Germany) ................................................................................ 212 Table 14. Instructions for post insertion of the RPR Prototype Titanium Post with KetacTM Cem Aplicap (based on manufacturer’s instructions) ................. 213 Table 15. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with Fuji Plus™ Capsule (based on manufacturer’s instructions) ................... 213 Table 16. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with RelyXTM Unicem Aplicap (based on manufacturer’s instructions) ............ 214 Table 17. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with Multilink® Primer/Multilink® Automix (based on manufacturer’s instructions) ................................................................................................................ 214 Table 18. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with LuxaBond®/LuxaCore® Z Automix (based on manufacturer’s instructions) ................................................................................................................ 215 Table 19. P-values for Kolmogov-Smirnov test of normal distribution of the pull-out force data, subdivided by post fit.. ........................................................... 216 Table 20. P-values for Kolmogov-Smirnov test of normal distribution of the pull-out force data, subdivided by luting system ................................................... 216 xii  Table 21. P-values for Kolmogov-Smirnov test of normal distribution of the pull-out force data, subdivided by luting system and post fit. ............................... 216 Table 22. Descriptive data for the pull-out force, subdivided by the post fit. ................................................................................................................ 217 Table 23. Descriptive data for the failure mode analysis, subdivided by the post fit. ................................................................................................................ 217 Table 24. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits. .................................................................. 217 Table 25. Descriptive data for the pull-out force, subdivided by the post fit. ................................................................................................................ 218 Table 26. Descriptive data for the failure mode analysis, subdivided by the luting system. .................................................................................................... 218 Table 27. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different luting systems. ........................................................ 218 Table 28. Descriptive data for the pull-out force, subdivided by the luting system for the congrunet post fit. .............................................................................. 219 Table 29. Descriptive data for the pull-out force, subdivided by the luting system for the medium incongruent post fit. .............................................................. 219 Table 30. Descriptive data for the pull-out force, subdivided by the luting system for the high incongruent post fit. .................................................................... 220 Table 31. Descriptive data for the failure mode analysis, subdivided by the luting system for the congrunet post fit. ............................................................. 220 xiii  Table 32. Descriptive data for the failure mode analysis, subdivided by the luting system for the medium incongrunet post fit. ............................................ 220 Table 33. Descriptive data for the failure mode analysis, subdivided by the luting system for the high incongrunet post fit. .................................................. 221 Table 34. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for Fuji Plus. ........................... 221 Table 35. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for RelyX Unicem. .................. 221 Table 36. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for Multilink Primer/Multilink. .. 222 Table 37. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for LuxaBond/LuxaCore Z. ..... 222  xiv  List of Figures Figure 1. Immature avulsed canine (tooth 23) in the oral cavity. ................................ 4 Figure 2. Immature intruded teeth 12 and 11, with the root tip of tooth 11 extending into the nasal cavity. ..................................................................................... 5 Figure 3. Immature avulsed central incisor (tooth 11), stored extraorally. .................. 5 Figure 4. Pulp necrosis (%) in immature and mature teeth after dislocation injuries. . 6 Figure 5. Pulp necrosis (%) in immature and mature teeth after dislocation with concommitant hard tissue (crown, crown-root or root fractures) injuries. ..... 6 Figure 6. Overview of vital pulp therapy treatment options with calcium hydroxide and MTA in immature teeth, aiming to achieve apexogenesis. ........................... 8 Figure 7. Micro-pulpotomy after crown fracture with pulp exposure of tooth 21. ....... 10 Figure 8. Overview of endodontic treatment options in immature teeth with a necrotic pulp, aiming to achieve apexification or apexogenesis. ............................. 13 Figure 9. Apexification in immature teeth 11 and 21. ................................................ 14 Figure 10. Artificial plug with MTA in immature tooth 12. .......................................... 15 Figure 11. Regenerative endodontic procedure in immature tooth 45. ..................... 18 Figure 12. Occurrence of a cervical root fracture after apexification with long-term calcium hydroxide application in immature tooth 21. ................................ 24 Figure 13. Restoration of central incisors after crown fractures with direct composite. ................................................................................................................. 27 Figure 14. Overview for reinforcement methods of endodontically treated immature teeth. ........................................................................................................ 28 xv  Figure 15. Artificial apical plug with MTA in immature tooth 21 and reinforcement with dual-cured composite. .............................................................................. 32 Figure 16. Artificial apical plug with MTA in immature tooth 11 and reinfocement with an individually formed post, made from a quartz fiber-reinforced composite splint material. .......................................................................................... 34 Figure 17. FRC-post reinforcement of the endodontically treated tooth 11 with thin root canal walls and significant coronal tooth structure loss. .................... 37 Figure 18. Illustration of the root canal diameter of mature and immature teeth in relation to conventionally available post systems. .................................... 38 Figure 19. Overview for the components and interfaces, involved in the adhesion of a luted post to root canal dentin. ................................................................. 49 Figure 20. Pull-out test design. ................................................................................. 55 Figure 21. Push-out test design. ............................................................................... 57 Figure 22. Micro-tensile test design with beam-shaped samples. ............................ 58 Figure 23. Micro-tensile test design with hourglass-shaped samples. ...................... 58 Figure 24. Macro-Lock Post Illusion with indications for diameters D1 and D2 ........ 64 Figure 25. Titanium post with indications for diameters D1 and D2 .......................... 64 Figure 26. Luting systems - overview of the conditioning, bonding and luting steps . 68 Figure 27. Flowchart of the experimental procedure ................................................ 69 Figure 28. Modified polypropylene mold ................................................................... 71 Figure 29. Wooden holder (sample holder A) for secure placement of five polypropylene molds, perpendicular to the table plane. ........................... 72 xvi  Figure 30. Plexiglass holder (sample holder B) for secure placement of five root samples along the root canal axis, perpendicular to the table plane. ....... 72 Figure 31. Root sample with two circular retention groves within the coronal 6 mm. 73 Figure 32. Embedding procedure of the root samples. ............................................. 74 Figure 33. Sample holder C ...................................................................................... 75 Figure 34. Sample holder D ...................................................................................... 76 Figure 35. Sample holder E ...................................................................................... 76 Figure 36. The 6 mm sample slice consisting of the embedded root segment. ........ 77 Figure 37. Plaster counterpart preparation. .............................................................. 78 Figure 38. Post fit for the FRC-posts, depending on the cavity and post size. ......... 79 Figure 39. Preparation of the sample for post cavity preparation. ............................ 80 Figure 40. Post cavity preparation. ........................................................................... 81 Figure 41. Post cavity enlagement in the sample slice. ............................................ 82 Figure 42. Preparation of the sample for post insertion. ........................................... 83 Figure 43. Post placement procedure. ...................................................................... 85 Figure 44. Separation of sample slice and counterpart. ........................................... 85 Figure 45. Removal of apical post protrusion. .......................................................... 86 Figure 46. Removal of apical post remnants. ........................................................... 87 Figure 47. Sample holder H for axial alignement of the posts with the parallelomenter ................................................................................................................. 88 Figure 48. Embedding procedure for pull-out testing. ............................................... 88 Figure 49. Pull-out testing procedure. ....................................................................... 90 Figure 50. Removal of the embedding resin. ............................................................ 91 xvii  Figure 51. Pull-out forces (N), subdivided by post fit and in relation with the control.96 Figure 52. Failure mode (%), subdivided by post fit. ................................................. 97 Figure 53. Pull-out forces (N), subdivided by luting system and in relation with the control....................................................................................................... 98 Figure 54. Failure mode (%), subdivided by luting system. ...................................... 99 Figure 55. SEM images of predominant failure between post and luting system. ... 100 Figure 56. SEM images of predominant failure between dentin and luting system. 101 Figure 57. SEM images of mixed failure between dentin and luting system and luting system and post. .................................................................................... 102 Figure 58. Pull-out forces (N), subdivided by luting system and post fit, in relation with the control. ...................................................................................... 103 Figure 59. Failure mode (%), subdivided by luting system and post fit. .................. 105  xviii  List of Abbreviations and Symbols %  Percentage α  Significance level α’  Local significance level C  Congruent Ca.  Circa  Ca(OH)2 Calcium hydroxide CEJ  Cemento-enamel junction CFV  Co-factor of variation °C  Degree Celsius D1  Diameter 1 (tip) D2  Diameter 2 (end) Di 3  Deciduous third lover bovine tooth Dr.  Doctor EDTA  Ethylenediaminetetraacetic acid E&RA  Etch & Rinse adhesive FAU  Friedrich-Alexander-University F_D  Failure within dentin F_D_LS Failure between dentin and luting system F_LS  Failure within luting system F_LS_P Failure between luting system and post Fmax  Maximal pull-out force F_P  Failure within post xix  FP  Fuji Plus FRC  Fiber-reinforced composite FRCP  Fiber-reinforced composite post  Ga  Gauge GIC  Glass ionomer cement GPa  Giga Pascal h  Hour/hours HIC  High incongruent post fit H2O  Water IQR  Inter quartile range KC_co Control group (titanium post, luted with Ketac Cem)  LC_LCZ LuxaBond/LuxaCore Z MIC  Medium incongruent post fit min  Minute/minutes MLP_ML Multilink Primer/Multilink MPa  Mega Pascal MTA  Mineral Trioxide Aggregate mW/cm2 Millie-watt per square centimeter n  Number N  Newton NaOCl Sodium hypochlorite p  P-value p.   Page xx  PDL  Periodontal ligament Ra  Surface roughness, absolute average of values RXU  RelyX Unicem Rz Surface roughness, average distance between highest peak and lowest valley s Second/seconds SCA  Self-conditioning adhesive SD  Standard Deviation UBC  University of British Columbia  xxi  Acknowledgements I would like to thank my supervisor Dr. Markus Haapasalo and the members of my research committee, Dr. Ya Shen, Dr. Rick Carvalho and Dr. Caroline Nguyen for their support and motivation. I always found an open door, a friendly and warm atmosphere and valuable feedback.  I would like to extend my grateful appreciation to Dr. Clive Roberts, who looked into my former career and academic accomplishments, and greatly supported me to find the right path at UBC.  I want to thank Dr. Dorian Ruse for his constructive critique and for a great afternoon, talking about the present study as well as research and academics in general. Your input helped to sort my thoughts, refine the process and improve the results.  Dr. Jolanta Aleksejuniene’s time and input, regarding the statistical analysis is greatly appreciated. It was very helpful to discuss different approaches and receive assurance to be on the right way.   For over ten years in Erlangen, I have been blessed to work with a wonderful research team, consisting of very smart and hardworking young dentists. You have been incredible co-workers, friends and family. Having all of you at my side certainly added to our overall achievement and experience. Thank you for your commitment and support.  xxii  My thanks are addressed to my former chairmen Prof. Dr. Anselm Petschelt, who always supported my clinical and scientific career with wisdom and patience. You enabled me to spread my wings, explore the world and almost always find my way back home. I very much appreciate that I was able to conduct the experiments in Erlangen.  Hans Löw’s help in manufacturing the sample holders and jigs for all our experiments is greatly appreciated. Without you, we would have not been able to ‘push and pull’.  I would like to thank Dr. Coil, and all our supervisors for the valuable input on Endodontics and your time and dedication. I also want to thank the staff for their outstanding work and help as well as my fellow students, who were great comrades. When I came from Germany to a new city and university, all of you extended your warmest welcome and support to make the transition easier. I learned a lot and found a new home and good friends. I will miss you!  I thank my husband and all my friends worldwide, who always supported me, even we don’t see each other very often. I promise, I will free up more time in the future.   Last but not least, I want to thank my parents for their steady support throughout my carrier and during my latest journey, here at UBC. You always have been a source of energy and knowledge for me, and you have guided me with patients, love and wisdom to become the person I am.  xxiii  Dedication        To my Parents, Family and Friends 1  Chapter 1: Introduction Endodontic treatment can be carried out to maintain teeth with pulpal and periapical disease in function, with the goal to remove or prevent infection of the root canal system and the periapical tissues. Microbial invasion can occur orthograde from the coronal site due to pulp exposure by trauma (1-7), decay (2, 8-13) or anatomical abnormalities (14-21). Another port of entry for microorganisms is from retrograde, through the apical foramen, after rupture of the apical pulp and exposure of the apical foramen due to severe dislocation injuries (3, 22-26). Depending on the developmental stage, immature teeth are characterized by thin root canal walls, wide root canals, short roots and an incompletely formed apical area with a large apical foramen. The main goal for these young teeth is to maintain pulp vitality, as a precondition to allow for further tooth development and maturation of the root (maturogenesis and apexogenesis) (27). However, in cases of pulp necrosis, root canal treatment is indicated. Because of the open apical foramen, additional measures are necessary to establish an apical barrier (apexification) in order to obturate the root canal system (28-32). Another possibility is to attempt a revitalization procedure to reestablish vital tissue in the root canal system, with the aim to allow for further root development (apexogenesis) (33-39).  Teeth treated with apexification methods remain structurally weak because of the thin root canal walls, and are prone to cervical horizontal or oblique fractures (32, 40-42). Often, teeth suffering from this type of fracture are not restorable and need to be extracted. Therefore, different methods are described for internal reinforcement of these teeth in order to support the weak tooth structure and reduce the fracture risk 2  (43-48). The most successful methods are based on adhesive techniques by bonding composite resin and reinforcement materials, such as fiber-reinforced composite posts (FRC-post), to the root canal dentin (43, 47-50). Multiple studies have been carried out to evaluate the bonding properties of these materials in mature teeth (51-60). However, in immature teeth, the conditions differ because of the large root canal diameter, which often exceeds the post diameter of commercially available FRC-posts, resulting in an incongruent post fit. Little is known about the influence of the post fit on the bonding properties of conventionally and adhesively luted FRC-posts.  This study is carried out to assess the influence of the post fit on the bonding properties, when using different conventional and adhesive luting systems for inserting FRC-posts. The results are compared with a gold standard (titanium post luted with conventional glass-ionomer cement), which was successfully used for decades when restoring structurally compromised teeth (61-63). 3  Chapter 2: Literature Review 2.1 Endodontic Treatment in Immature Teeth  Endodontic interventions in immature teeth can be indicated in teeth with an inflamed, vital pulp or in teeth with a necrotic pulp. Reasons for pulpal or periapical disease can be carious lesions (2, 8, 11, 64, 65), hard tissue traumata and/or dislocation injuries (1, 3, 5, 6, 8, 66) as well as anatomical abnormalities, such as dens invaginatus (8, 15, 20, 21) or dens evaginatus (8, 14, 17, 67). Caries is a multifactorial disease leading to destruction of dental hard tissues, such as enamel, dentin and cementum (68, 69). Bacteria invade the destructed dentin and can cause pulpal inflammation. With continuous progression of the carious lesion towards the pulp, bacteria and their toxic byproducts invade the pulp (9, 70), leading to inflammation, followed by pulpal necrosis. The inflammation starts at the port of entry and progresses over time towards the apical area (70-72).  Dental hard tissue traumata, such as crown fractures and crown-root-fractures, can lead to pulpal exposure to the oral cavity with bacterial invasion. In teeth without concomitant dislocation injuries, the bacterial invasion of the pulp is delayed because of the intact immune defense of the vital, previously healthy, pulp. A histological study on monkeys with artificially exposed pulps shows that inflammatory reaction progresses on average only 1.8 mm (1.5 – 2.0 mm) after 2 days and 1.6 mm (0.8 – 2.2 mm) after 7 days from the exposure site apically into the pulp (73). Therefore, techniques aiming to maintain pulp vitality are indicated to promote tooth maturation. Dislocation injuries can lead to rupture of the pulp at the apical foramen. Depending on the severity of the injury and the degree of dislocation, the pulp can 4  become infected, when bacteria reach the pulp through the apical foramen due to exposure to: i. the oral cavity (severe extrusive or lateral dislocation and avulsion) (Figure 1, p. 4), ii. nasal cavity (intrusive dislocation) (Figure 2, p.5) or iii. extra-oral environment (avulsion) (Figure 3, p.5).   Figure 1. Immature avulsed canine (tooth 23) in the oral cavity. The root surface, the apical foramen and the ruptured apical pulp are exposed to saliva and microorganisms.  The frequency of pulp necrosis, after dislocation injuries in immature teeth, increases with the severity of the injury (5-7, 74-77). However, teeth with mild and moderate dislocation injuries and rupture of the pulp often undergo pulp revascularization, after repositioning (74, 78, 79) (Figure 4, p. 6) however, the likelihood for revascularization or pulp survival decreases considerably when concomitant dental hard tissue injuries (i.e. crown fracture, crown-root fracture) are present (5-7, 74, 75, 77) (Figure 5, p. 6). 5   Figure 2. Immature intruded teeth 12 and 11, with the root tip of tooth 11 extending into the nasal cavity. The apical foramen and ruptured apical pulp are exposed to the nasal environment and microorganisms.   Figure 3. Immature avulsed central incisor (tooth 11), stored extraorally. The root surface, the apical foramen and the ruptured apical pulp are exposed to the extraoral environment and microorganisms . 6   Figure 4. Pulp necrosis (%) in immature and mature teeth after dislocation injuries. Green indicates high chance for pulp survival, red for pulp necrosis. Arrows encompass percentage range for pulp necrosis fequency from different studies (3, 4, 24, 74, 75, 77, 80-83).   Figure 5. Pulp necrosis (%) in immature and mature teeth after dislocation with concommitant hard tissue (crown, crown-root or root fractures) injuries. Green indicates high chance for pulp survival, red for pulp necrosis. Arrows encompass percentage range for pulp necrosis fequency from different studies (3-7, 74-77, 79-81, 84).  7  Dens invaginatus is an anatomical tooth abnormality that presents with a deepening or invagination of the enamel organ into the dental papilla during tooth development (85), resulting in a possible pathway for bacteria to invade the pulp. The prevalence varies in different studies between 0.3 and 26.1% with a higher incidence in mongoloid ethnicities (86-88). The most commonly affected teeth are maxillary lateral incisors (86, 89, 90). The more severe invaginations (Oehlers Type II and III) (91) result in a higher risk for the development of pulpal and periapical pathosis (88, 91-93). The incidence of pulp necrosis was found to be ca. 11% in an observational study (88, 94). Dens evaginatus, often called Talon cups in incisors, describes a rare anatomical tooth abnormality with a multifactorial etiology that is likely influenced by genetic and environmental factors, predominantly occurring in premolars (17). The prevalence is significantly higher in the Asian (17), Alaskan Native and North American Aboriginal population (17, 95, 96). The evagination presents as a cusp-like tubercle that often contains pulp tissue (70%) (17, 97). Due to fracture of the evaginated cusp - when the tooth reaches the occlusion level - the pulp becomes exposed to the oral cavity, often resulting in pulp necrosis at an early developmental stage of the tooth (17).  2.1.1 Teeth with Vital Pulp  The main goal in immature teeth with partial pulpal pathology is to maintain pulp vitality to allow for maturogenesis (27). Maturogenesis includes dentin apposition to the thin root canal walls, development of the tooth to its full length and completion 8  of the root apex formation (apexogenesis). Depending on the suspected depth of bacterial invasion and progression of the inflammation, different vital pulp therapy methods are indicated, such as direct pulp capping (98-104), micro-pulpotomy (105-108) and pulpotomy (10, 109-115) (Figure 6, p. 8).   Figure 6. Overview of vital pulp therapy treatment options with calcium hydroxide and MTA in immature teeth, aiming to achieve apexogenesis. A - Direct pulp capping; B - Micro-pulpotomy; C - Pulpotomy  Direct pulp capping includes the superficial disinfection of the exposed pulp, followed by placing a separate wound dressing (i.e. calcium hydroxide) and a bacterial tight seal (101-103)(Figure 6 A, p. 8) or by placing a biocompatible filling 9  material directly on the exposed pulp (i.e. MTA) (99, 102) (Figure 6 A, p. 8). Direct pulp capping is indicated in cases of short-term traumatic exposure of a previously healthy pulp, resulting in a high pulp survival rate (2, 100, 116, 117). Some studies demonstrate evidence that direct pulp capping can also be successfully used after pulpal exposure in cases of deep carious lesions. However, the literature is controversial about this indication because after carious exposure, the pulp shows chronic inflammation of a clinically unpredictable extend, which can considerably reduce the success rate (2, 9, 13). Therefore, strict selection criteria must be applied when choosing this treatment option. Cvek first described the micro-pulpotomy procedure in 1978 (105). It involves the removal of small infected and inflamed parts of the exposed pulp, followed by capping with a wound dressing (i.e. calcium hydroxide) (105, 107, 108) (Figure 6 B, p. 8) and a bacterial tight filling or by capping with a biocompatible filling material (i.e. MTA) (111) (Figure 6 B, p. 8). This method is indicated after traumatic (105, 106, 108) (Figure 7, p. 10) or carious pulp exposure (105, 107) and can also be considered at early stages of pulpal involvement in dens invaginatus (118) and dens evaginatus cases (17). The rate for pulp survival is high (90-96%) (10, 100, 119, 120) because inflamed pulp tissue, invaded by microorganisms, is removed, before placing the capping material.    10   Figure 7. Micro-pulpotomy after crown fracture with pulp exposure of tooth 21. After micro-pulpotomy, the pulpal wound was dressed with calcium hydroxide and the fragment was adhesively reattached. The pulp remained vital, leading to maturogenesis and apexogenesis. A thick dentinal bridge was found in the follow-up radiographs (1, 2 and 4 years). The clinical picture shows a yellow opaque discoloration of tooth 21, except for the reattached fragment, as a signs of extensive internal hard tissue apposition at the former micro-pulpotomy site.   Pulpotomy involves the removal of the entire coronal pulp tissue, before placing the capping and filling material (110, 114, 115). The pulpal stump is then covered with a wound dressing (i.e. calcium hydroxide) and a bacterial tight filling (110, 114, 115) (Figure 6 C, p. 8) or with a biocompatible filling material (i.e. MTA) (111) (Figure 6 C, p. 8). This technique is indicated in cases where progression of 11  bacterial invasion and inflammation is suspected to involve the coronal pulp but not the radicular pulp. Indications are long-term traumatic pulpal exposure, carious exposure and pulpal involvement in cases of anatomical abnormalities (10, 17, 109, 111, 112, 115, 118). The advantage of performing a pulpotomy, compared to a pulpectomy in immature teeth, is the continuous maturation of the root including apexogenesis (27, 109, 112). Subsequent root canal treatment, after completion of the root development and before extensive root canal calcification occurs, is critically discussed (121-123). The success rate for pulpotomy varies, depending on the condition causing the pulpal involvement (72-79%) (121, 124), however, it is lower compared to pulp survival after micro-pulpotomy. The difference in pulp survival could be explained by the clinical indication for the two treatment methods. The ideal outcome after vital pulp therapy is first, to achieve and maintain a healthy vital pulp and secondly, the formation of a hard tissue barrier by newly formed odontoblast-like cells at the exposure site. Clinical success can be considered when the tooth is functional, the pulp is vital and the patient does not experience discomfort, even when no hard tissue barrier has formed. Unsuccessful treatment outcome is characterized by irreversible pulpitis, pulp necrosis and/or periapical pathosis.   2.1.2 Teeth with Pulp Necrosis In cases when vital pulp therapy was not successful or the pulp is necrotic, conventional root canal treatment is indicated. It consists of disinfection of the root canal system, obturation of the cleaned root canal and restoration of the tooth with a 12  bacterial tight seal. The methods for disinfecting the root canal, the dentinal surface and the dentinal tubules differ in immature teeth from the chemo-mechanical preparation and disinfection techniques, used in mature teeth. The root canal of immature teeth is already large and allows insertion of an irrigation needle, without prior shaping of the root canal walls. In addition, mechanical preparation of the root canal dentin should be avoided because of the thin and structural weak root canal walls. Therefore, disinfection should involve copious irrigation with sodium hypochlorite and mechanical, sonic or ultrasonic activation of the irrigation solution to reduce and control the microbial invasion (125-129). The reported sodium hypochlorite concentrations vary from 0.5 – 5.0% (127, 130-132) however, for apexification procedures, no common recommendation could be found. For teeth undergoing regenerative endodontic therapy, the American Association of Endodontics recommends low sodium hypochlorite concentrations (1.5 %) because of the potential toxicity for stem cells (133). However, when using EDTA as a final rinse, the toxic effect of sodium hypochlorite can be reduced or eliminated (134-136). Subsequent inter-appointment dressing of the root canal with antimicrobial substances (i.e. calcium hydroxide or antibiotic pastes) can further help to reduce the microbial load (132, 137-140). After disinfection, the root canal system should be obturated to reduce the risk for re-infection. Because of the wide apical foramen in immature teeth, the creation of an apical barrier is most desirable, before using conventional root canal filling techniques (Figure 8, p. 13).  13   Figure 8. Overview of endodontic treatment options in immature teeth with a necrotic pulp, aiming to achieve apexification or apexogenesis. A - Apexification with long-term calcium hydroxide application; B - Apexification with introduction of an apical MTA plug; C - Regenerative endodontic procedure   As early as in the1960’s, a technique for inducing an apical hard tissue barrier (apexification) was introduced (31) (Figure 8 A, p. 13). The treatment consists of disinfecting the root canal system, followed by long-term, repeated intra-canal calcium hydroxide application, until a hard tissue barrier can be detected (31, 141, 142) (Figure 9, p. 14).   14   Figure 9. Apexification in immature teeth 11 and 21. The 8 year old patient presented after an accident with crown fractures and pulp exposure. Pulpectomy, instead of vital pulp therapy, was performed during emergency treatment. The teeth were then treated with long-term Ca(OH)2 application, until a solid apical barrier was achieved. The root canals were filled with gutta percha and covered with resin composite.  The hard tissue barrier can consists of bone, dentin or cementum however, it is usually a compound of these hard tissues (143, 144). The treatment duration varies between 3 and 20 months (30, 42, 131, 145). Disadvantages of this method are: i. long treatment intervals, ii. need for changing the intra-canal dressing, iii. decreasing compliance of the young patients over the treatment course, iv. possibility for reinfection between the appointments, v. reduction of mechanical properties of the 15  dentin and vi. occurrence of fatal cervical root fractures during or after the apexification procedure (32, 41, 42, 146, 147). Despite the above-mentioned disadvantages, the method was successfully applied for decades, and multiple clinical studies show a reasonable or high success rate (74-100%) (148-151).  Another, more practical and elegant method to successfully generate an apical barrier was developed, when MTA was introduced to the market in the 1990’s (152-155). After disinfection of the root canal system, MTA can be applied as an apical plug to generate an artificial barrier (32, 156-158) (Figure 8 B, p. 13, Figure 10, p. 15).  Figure 10. Artificial plug with MTA in immature tooth 12. The patient presented with previously initiated root canal treatment and asymptomatic apical periodontitis (tooth 12). After root canal treatment, the entire canal was filled with MTA. 16  The advantages of this method are: i. short treatment intervals (one or two appointments), ii. low risk for reinfection between the appointments and iii. higher acceptance of the treatment regime by the patients. MTA is a highly biocompatible material that supports healing and hard tissue apposition (28, 29, 32). The handling properties of MTA and the possible need for using a dental surgical microscope for placing the material as an apical barrier could limit this procedure to be carried out by dentists, specialized in endodontics. The success rate of over 95% for this method is comparable or higher than the apexification with long-term calcium hydroxide placement (28, 32, 150, 159).  After successful barrier generation (apexification or artificial apical barrier), the root canal system can be obturated with conventional filling techniques using gutta percha and sealer (i.e. warm vertical compaction, lateral condensation, individualized single cone technique) (160-162). Then, the tooth is restored with a bacterial tight seal (i.e. adhesive resin-composite filling) to reduce the risk of reinfection of the root canal system. Since the 2000’s, several case reports (38, 125) and case-controlled studies (148, 150, 163-166) have been published about pulp regeneration procedures (Figure 8 C, p.13). The methods aim to reestablish vital tissue - ideally pulp tissue - in the disinfected root canal of a tooth with pulp necrosis and apical pathosis, which provides the conditions for further tooth maturation and apexogenesis (38, 148, 166) (Figure 11, p. 18). Several techniques have been described (38, 125, 139, 167-170), requiring the following components and conditions: i. disinfected root canal system, ii. absorbable scaffold, iii. stem cells, iv. growth factors and v. bacterial tight seal (171-17  173). Clinically, the disinfection can be carried out by sodium hypochlorite irrigation, with possible subsequent inter-appointment, intra-canal medication, using antibiotic pastes (38, 125, 170) or calcium hydroxide (167-169). The release and/or exposure of growth factors, fossilized in the dentin during tooth development, are achieved by using EDTA as a final rinse (134, 174). The introduction of a scaffold into the empty root canal and the population with stem cells are accomplished by inducing bleeding from the apical tissue and dental papilla, resulting in the formation of a blood clot in the root canal (39, 125, 175). The blood clot is then covered with a biocompatible, well-sealing material (i.e. MTA), followed by an adhesive resin composite filling to generate a bacterial tight seal (125, 167, 175, 176).  Advantages of the method are continuation of root development, short treatment intervals and good patient compliance. Disadvantages are the possible use of locally applied antibiotic pastes for root canal disinfection, which can lead to the development of bacterial resistance or allergies. The occurrence of moderate to severe discolorations, when using antibiotic pastes, containing tetracycline derivatives, is a common sequel (166, 177, 178). In addition, dentin apposition only occurs in areas, where vital tissue populates the root canal space, which does not include the fracture prone weak cervical area. Success rates range from 78-100% (39, 148, 150) however, a reliable evaluation cannot be made because long-term clinical studies with sufficient sample size are not available.  18   Figure 11. Regenerative endodontic procedure in immature tooth 45. The patient presented with pulp necrosis and chronic apical abscess with a draining sinus tract. A dens evaginatus, which had been previously reduced and covered with adhesively bonded composite, was identified as the source for the pulpal infection. The tooth was endodontically treated. In the second appointment, a blood clot was introduced into the canal and covered with MTA and a fiber-reinforced composite filling. The 1 and 2 year follow-up revealed no clinical and subjective symptoms. The radiographs show a complete resolution of the apical radiolucency, apexogenesis and pulp canal calcification below the MTA filling.  REG ENDO = Regenerative endodontic procedure  19  2.1.3 Complications after Completed Endodontic Treatment 2.1.3.1 Periapical Pathosis Periapical pathosis includes pathologic changes of endodontic origin in the periapical tissues, which are clinically diagnosed as asymptomatic or symptomatic apical periodontitis as well as chronic or acute apical abscess (179). Histologically, the lesions can be characterized as apical granuloma, radicular cyst or foreign body reaction of different origin. Causes are predominantly of microbial nature however, non-microbial stimuli are also contributing to the development of periapical disease (180-182). Multiple studies, focusing on the incidence of different periapical lesions, have been conducted on mature teeth (183-187). However, data for immature teeth are scarce and studies do not discriminate between the different histological or clinical features. The incidence of apical pathosis after root canal treatment in immature teeth is reported to be 4-8% (41, 151, 188-191).  2.1.3.1.1 Periapical Pathosis Caused by Microorganisms The majority of periapical pathosis is a result of microbial invasion (180, 192-194). Bacteria and fungi - with decreasing frequency - are found in isolates from the root canal space and surrounding root canal dentin (195-201). The microorganisms reside mainly within the confines of the root canal system (intra-radicular infection) (202-205) because the immune defense is usually capable to eliminate microorganisms in areas with sufficient blood supply, such as the periapical tissues. However, in some cases (4-6%), microorganisms can be found on the external root surface or within the apical lesion (extra-radicular infection) (202-204, 206).  20  If the apical pathosis is purely of microbial origin, elimination of the infection results in complete healing (180, 207, 208). Persistent infection indicates that intra- or extra-radicular microorganisms are remaining after the completion of the root canal treatment. The microbial load is above the threshold to sustain periapical pathosis (164, 180, 209, 210). Reasons for persistent intra-radicular infection can be remaining microorganisms in: i. missed canal anatomy (i.e. additional canals, anastomoses, lateral canals, apical deltas, fins), ii. on the root canal walls and iii. in the dentinal tubules (180, 211, 212). Endodontic treatment options to eliminate the bacteria are, either orthograde retreatment or surgical retreatment by apicoectomy and retrograde root canal filling, or a combination of both (210, 211, 213, 214). Extra-radicular microorganisms were found to reside in long-standing asymptomatic apical periodontitis lesions in the granulation tissue as well as in the form of biofilm on the root surface (202-204, 206, 215). These microorganisms cannot be eliminated with orthograde root canal retreatment and therefore, a surgical approach (apicoectomy, removal of the apical lesion and retrograde root canal filling) is the appropriate endodontic treatment option, possibly combined with an orthograde retreatment, when intra-canal persistent infection is also suspected (206, 213, 216, 217). Reinfection of a previously successfully disinfected root canal system occurs when microorganisms from the outside leak into the tooth or root. Coronal leakage (orthograde) can occur via: i. missing or incompletely sealed restorations, ii. exposed dentinal tubules and iii. carious lesions (180, 205, 218, 219). Lateral leakage can be the consequence of exposed dentinal tubules, as well as lateral or furcation canals in 21  periodontally compromised or treated teeth with attachment loss and/or pockets (180, 220). Apical leakage (retrograde) can take place when the root tip is exposed to microorganisms as i.e. in periodontally compromised teeth, where the pocket reaches the apical area or after avulsion where the root is completely exposed to the oral or extra-oral environment (180, 214, 221). The main goal after endodontic treatment is therefore, to prevent leakage in order to avoid ingress of microorganisms via the above-mentioned routes.  2.1.3.1.2 Periapical Pathosis of Non-microbial Nature Persistent apical pathosis can be in some instances also of non-microbial origin. Radicular periapical cysts (true cysts and bay cysts) have an incidence between 5 and 55%, depending on the study and the applied histological techniques (181, 222, 223), and can be a cause for persistent apical pathosis, which does not resolve by orthograde endodontic treatment (181, 211, 224).  Another cause for persistent apical pathosis are foreign body reactions in response to a variety of materials and substances. Exogenous materials, capable of causing a foreign body reaction in the periapical area, are dental materials (i.e. gutta percha particles, restorative materials) and vegetable food particles (oral pulse granuloma) (182, 225, 226). Endogenous substances, causing foreign body reactions, are fine crystal particles (182). Cholesterol crystals are found in non-healing apical lesion. Immune cells, such as macrophages, are not capable of eliminating these larger size crystals, which leads to an accumulation of the crystals and persistence of the apical lesion (182, 227). Apical pathosis, caused by foreign 22  body reactions, cannot be successfully treated by orthograde endodontic treatment. A surgical approach, including apicoectomy, removal of the entire apical lesion and retrograde root canal filling, is indicated (182, 214). The surgical approach can be combined with an orthograde root canal retreatment, when persistent intra-canal infection is suspected.   2.1.3.2 Fractures 2.1.3.2.1 Vertical Root Fractures Occasionally, vertical root fracture can occur in a tooth that has undergone root canal treatment. In such cases, a vertical root fracture occurs months or years after the completion of the root canal treatment (228-234). They are usually located on the buccal and/or lingual root side. Possible diagnostic findings include the patient’s chief complaint (i.e. occurrence of a sinus tact, bad taste in the area, tenderness of the tooth, tooth mobility), clinical findings (i.e. isolated deep pockets, single or multiple sinus tracts, increased tooth mobility, fracture line) and radiographic findings (i.e. J-shaped lesion) (235-237). The cause of vertical root fractures is believed to be multifactorial: i. weakening of the root canal dentin by mechanical preparation (i.e. root canal shaping, post space preparation) and chemical agents (i.e. sodium hypochlorite, chelating agents, calcium hydroxide), ii. application of notch stresses by root canal and post space preparation or insertion of screw-type posts, iii. application of force to the root dentin by root canal filling techniques (i.e. lateral or vertical compaction), iv. insertion of posts with a modulus of elasticity higher than dentin, especially if no sufficient ferrule 23  effect is achieved, v. trauma and occlusal forces. The mechanism for the development of vertical root fractures is believed to be dynamic and is usually initialized by the induction of cracks, which propagate over a period of time, until detectable fractures can be verified (231, 238-243). Information on the occurrence of vertical root fractures in endodontically treated immature teeth is very scarce. Two case reports were found in the literature (244, 245). In addition, two cases of vertical root fracture, in teeth treated with a MTA plug after dental trauma, were identified in the author’s own patient collective. Colleagues, involved in the treatment of dental trauma in children (Prof. Dr. Kurt Ebeleseder, University Graz, Austria and Prof. Dr. Gabriel Krastl, University Würzburg, Germany) also reported the occurrence of these fractures after MTA plug application as a rare sequel (personal communication).  At this time, there is no known successful treatment for teeth with vertical root fractures, and therefore, the only viable treatment option is the extraction of the affected tooth.   2.1.3.2.2 Cervical Horizontal or Oblique Fractures  The mechanical properties of dentin were found to be similar in vital and non-vital teeth (246, 247) while a recent study found nano-structural differences (248). However, chemical agents, used in root canal disinfection, such as sodium hypochlorite, EDTA and long-term intra-canal dressing with calcium hydroxide, can alter the mechanical properties and reduce the fracture resistance of the dentin (249-24  256). In addition, in immature teeth, the root canal walls are thin, and endodontic access preparation can weaken the tooth structure further (Figure 12, p. 24).   Figure 12. Occurrence of a cervical root fracture after apexification with long-term calcium hydroxide application in immature tooth 21. The patient presented with pulp necrosis and asymptomatic apical periodontitis on tooth 21 and replacement resorptions on the previously root canal treated tooth 11. Teeth 12 (lateral dislocation), tooth 11 (avulsion and crown fracture) and tooth 21 (lateral dislocation and crown fracture) were injured, 4 years prior to presentation, during a bike accident.  On tooth 21, root canal treatment was performed and long-term calcium hydroxide applied for apexification, until a solid apical hard tissue barrier was detected (after 18 month). The root canal was filled with gutta percha and the access was closed with a composite filling. During the course of the treatment of tooth 21, tooth 11 underwent decoronation. One year after root canal filling and 1 month after insertion of a FRC Maryland-bridge, the patient presented with cervical root fracture of tooth 21 (arrow) and cervical resoprtion of tooth 12. 25  Another aspect, contributing to an increased fracture risk of endodontically treated teeth, is the reduction in pressure detection in pulpless teeth (257, 258). Taking all these factors into consideration, immature teeth carry an increased risk to suffer cervical horizontal or oblique fractures. Teeth with these types of fracture are often not restorable and need to be extracted (Figure 12, p. 24). In a clinical study (4 year follow-up, immature teeth n = 397, mature teeth n = 362), Cvek demonstrated a higher incidence of cervical fractures in immature teeth (40%), treated with long-term calcium hydroxide intra-canal dressing for apexification, compared to a significantly lower incidence in endodontically treated mature teeth (2%). The frequency of cervical root fractures decreased significantly with progressing tooth development (stage 1 = 77%, stage 2 = 53%, stage 3 = 43%, stage 4 = 28%). The cervical fractures occurred 61% of the time during the calcium hydroxide apexification procedure and 39% of the time after the root canal filling. The majority of the fractures occurred within months and up to 3 years (63%) (41). Comparable clinical studies, regarding the fracture incidence in teeth, treated with an apical MTA plug or with regenerative endodontic therapy, are not available.  2.2 Post-endodontic Restoration After the completion of endodontic treatment, the tooth should receive a post-endodontic restoration in a timely manner. The goals, of intra-canal and/or coronal restorations are: i. a bacterial-tight seal to prevent reinfection of the root canal system, ii. stabilizing and strengthening the weakened tooth structure and iii. restoring the tooth in form and function (259-263). The restoration of immature teeth can 26  require different techniques, compared to mature teeth, since the root canals are wide and the canal walls are thin and weak. Teeth requiring endodontic treatment after trauma (i.e. dislocation injuries), often show an intact natural crown or minimal hard tissue loss. In addition, teeth in young patients are usually not fully erupted, which results in the exposure of the margins of indirect restorations over time, when these are placed at an early age. Therefore, the state-of-the-art restoration for mature teeth, with partial or complete crowns, is often contraindicated in immature teeth. Immature teeth can and should be restored using acid-etch technique (264) in combination with adhesively bonded direct resin composite restorations or fragment reattachment. These types of restorations are minimally invasive, preserve tooth structure, are reversible, can be adapted according to the changes in the growing patient and stabilize the tooth structure (52, 265-268) (Figure 13, p. 27). 27   Figure 13. Restoration of central incisors after crown fractures with direct composite. After root canal treatment and bleaching, tooth 11 is restored with a FRC-post for strengthening the thin root canal walls and to improve the retention of the adhesive direct composite built up. Tooth 21 is also restored with an direct composite built-up. (Reprinted with permission of John Whiley and Sons (52)  2.2.1 Reinforcement of Endodontically Treated Immature Teeth  Endodontically treated immature teeth are structurally weak and prone to cervical root fractures, when the root canal is filled conventionally with gutta percha up to the CEJ, followed by the application of a filling material for access closure (41). Different methods for internally reinforcing and strengthening these teeth have been described over the last decade (43-48, 269). All methods have in common that the 28  reinforcing material should extend apically beyond the crestal bone level to support and strengthen the fracture prone cervical area. Different reinforcing materials and material combinations have been introduced, which can be subdivided in three categories: i. conventional or bioceramic cements (i.e. glass ionomer cement, MTA) (48, 270-273), ii. adhesively bonded resin composites (44-46, 48, 274) and iii. adhesively luted fiber-reinforced composite materials (43, 44, 46-48, 275) (Figure 14, p. 28).   Figure 14. Overview for reinforcement methods of endodontically treated immature teeth. After root canal treatment, an apical MTA Plug is inserted as an artificial barrier. The reinforcements are introduced into the root canal, including the fracture prone cervical area. NAB = Non-adhesive bonding, FRC = Fiber-reinforced 29  The majority of studies, testing fracture resistance of internally reinforced endodontically treated immature teeth, found that adhesively luted fiber-reinforced materials showed the highest increase in fracture resistance, followed by adhesively luted resin composite and conventional or bioceramic cements (44, 47, 48).   2.2.1.1 Bioceramic Cements Cements are dental materials, consisting of a powder and a fluid component, which are usually self-curing after mixing. Cements are brittle materials with inferior mechanical properties (i.e. compressive strength, flexural strength, modulus of elasticity, abrasion stability) compared to resin composites (276-281). Physical properties, such as: i. chemical bonding to tooth structure, ii. low volumetric and linear shrinkage, iii. good marginal seal, iv. fluoride release (caries-protective effect), v. high biocompatibility and bioactivity and vi. easy handling, are considerably superior compared to resin composites, and make them a desirable dental material for certain indications (277, 282-284). Modifications, such as the addition of reinforcing particles or fibers and the addition of resin components, generate cement materials with improved mechanical properties (285-287). Because of the chemical bonding to tooth structure and the good sealing ability, bioceramic cements (i.e. glass-ionomer cement, mineral trioxide aggregate, calcium-enriched mixture cement) are recommended to seal the canal orifices after root canal filling with gutta percha (288-290). In addition, in vitro studies have shown that the application of classical or resin-reinforced glass ionomer cement (45, 271) mineral trioxide aggregate (48, 270, 272) or calcium-enriched mixture cement (291) 30  as an intra-canal reinforcement material (involving the fracture prone cervical area or the entire root canal) can increase the fracture resistance of simulated immature teeth. The potential of bioceramic cements (i.e. MTA) to cause moderate to severe discolorations should be taken into account when using these materials in the esthetic zone (292-295).  2.2.1.2 Resin Composite Resin composite materials are widely used in modern dentistry (i.e. direct or indirect restorations, fissure sealing, luting of posts or indirect restorations, filling repair, adhesive re-cementation of tooth fragments) (296-298). Advantages are: i. the aesthetic appearance, ii. tooth structure preserving preparations, iii. cost effectiveness, compared to indirect restorations and iv. bonding to dental hard tissue via dental adhesives, resulting in strengthening of the tooth structure (296-300). The main disadvantage of resin composites is the polymerization shrinkage, leading to gap formation and development of recurrent decay. To counterbalance the negative effect of the polymerization shrinkage, adhesive bonding of the composite to the tooth structure and special application techniques (i.e. incremental filling) are used to achieve clinically acceptable long-term results (301-306). In addition, the durability of resin composite restorations can be inferior under certain circumstances (i.e. large restorations, high caries risk patients), compared to amalgam or indirect restorations (298, 300, 307-309). The successful use of dental adhesives and resin composites is more challenging and technique-sensitive, compared to other dental materials, and 31  requires sound knowledge and understanding of the bonding mechanisms and material properties (298, 299, 308).  Dental materials, suitable for reinforcing immature teeth after endodontic treatment, should have a modulus of elasticity close or similar to dentin and good mechanical properties, such as high flexural, tensile and compressive strength. Bonded resin composites usually fulfill these requirements (298, 309, 310). From a practical point of view, the use of light curing flowable or packable bonded composites is possible (Figure 15, p. 32). Care has to be taken to apply these materials void-free and to ensure that the curing light energy is sufficiently high to reach the deeper canal areas for optimal polymerization of the adhesive and composite resin material (311, 312). Dual-or chemical curing core build-up or luting resin composites are also indicated as reinforcement material with the advantage that curing in deeper canal areas is ensured by chemical initiation of the polymerization, independent of the light transmission (313-315).  In vitro evaluations on simulated immature teeth show that teeth, reinforced with bonded resin composite, achieve fracture resistance values comparable to mature teeth (46) however, the strengthening capability is significantly lower compared to teeth, restored with fiber-reinforced materials (44, 47).   32   Figure 15. Artificial apical plug with MTA in immature tooth 21 and reinforcement with dual-cured composite. The patient presented with pulp necrosis, asymptomatic apical periodontitis and external infection-related root resorptions on tooth 21. The tooth suffered from a lateral dislocation during a playground accident, 2 years prior to presentation. The tooth was not repositioned or splinted after the accident. Root canal treatment was performed and an apical MTA plug inserted before root canal filling with gutta percha (ca. 3 mm). The remaining canal space was filled with a bonded dual-cured composite and the access was closed with a composite filling.   2.2.1.3 Fiber-reinforced Composite Materials Resin composite materials alone show only limited fracture resistance and flexural strength (44, 47). Therefore, it is most desirable to improve the mechanical properties of resin composites by adding reinforcements, such as fibers (i.e. Kevlar®, 33  polyethylene fibers, quartz fibers, glass fibers). Different commercially available materials (i.e. Ribbond® Ribbond, Seattle, USA; Quartz SplintTM, Saint Égrève, RTD, France, GrandTEC®, VOCO, Cuxhaven, Germany) can be used for reinforcing structurally weak teeth (47, 275, 316), strengthen direct or indirect restorations (i.e. bridges, dentures) (317-323) or splint periodontally (324, 325) or traumatically (326, 327) compromised teeth.  Ribbond is made from woven polyethylene fibers, which are not pretreated with resin by the manufacturer. The advantages of this reinforcement material are: i. high tensile strength, ii. unlimited shelf life and iii. versatile range of applications (321, 328, 329). The woven fiber band can be easily penetrated with unfilled resin or flowable composite however, no chemical bond is generated between the fibers and the resin material. Fiber-reinforced materials, such as Quartz Splint (unidirectional, rope or woven fibers) (326, 330) (Figure 16, p. 34) or GrandTEC (unidirectional fibers) (331, 332) consist of silanized fibers, which are infiltrated with resin by the manufacturer and ready to use. In addition to high tensile strength and versatile application of the materials, the main advantage of these materials lays in the silanization of the fibers, which ensures a chemical bonding between the fibers and the resin matrix, resulting in considerably better mechanical properties (330, 331, 333).  Another advantage, when using these reinforcement materials, compared to conventional FRC-posts, is that chemical bonding to the reinforcement material surface is possible after polymerization because of the presence of free radicals and remaining double bonds in the superficial oxygen-inhibition layer (331, 332, 334, 34  335). The modulus of elasticity of these materials is comparable with conventional FRC-posts and dentin (333).   Figure 16. Artificial apical plug with MTA in immature tooth 11 and reinfocement with an individually formed post, made from a quartz fiber-reinforced composite splint material. The patient presented with previously initiated root canal treatment, acute abscess and external infection-related root resorption on tooth 21. The tooth was avulsed, one year prior, due to a sports-related accident. Root canal treatment was performed with long-term calcium hydroxide application for 6 months. Then an apical MTA plug was inserted, before filling the remaining root canal with an individually formed fiber-reinforced post, luted with a dual-cured resin composite luting system. The access was closed with a composite filling.   Two studies on simulated immature teeth, using an adhesively luted Ribbond reinforcement, compared to unfilled root canals or teeth reinforced with adhesively 35  bonded composite, were identified. The Ribbond®-reinforced teeth achieved significantly higher facture values, compared to the other two groups (47, 275). Unpublished data (publication in preparation) from our research group (Friedrich-Alexander-University, Dental Clinic 1 – Operative Dentistry and Periodontology, Germany), testing the reinforcement properties of different materials on simulated immature teeth, found a significant increase in fracture resistance when using adhesively luted Quartz Splint as reinforcement material. The load, required to fracture these specimen, considerably exceeded the fracture load of unprepared mature teeth (Table 2, p. 35).  Table 2. Fractue load (N) of mature and simulated immature teeth, reinforced with different techniques and materials (unpublished data).  MLXRO = Macro-LockTM Post Illusion X-RO, QFS = Quartz SplintTM, SD = Standard deviation  Tooth Status Reinforcement Method Fracture Load (N)  Mean ±SD Mature Tooth None 934.2 ±213.7 Immature Tooth None 770.6 ±161.6 Immature Tooth Gutta Percha 906.6 ±195.9 Immature Tooth Biodentin 971.5 ±194.8 Immature Tooth LuxaBond/LuxaCore Z 963.4 ±212.5 Immature Tooth MLXRO + LuxaBond/LuxaCore Z 1138.3 ±211.2 Immature Tooth QFS + LuxaBond/LuxaCore Z 1257.2 ±200.5 Immature Tooth QFS + MLXRO + LuxaBond/LuxaCore Z 1323.8 ±263.4  2.2.1.4 Posts  As early as in the 16th century in Japan, experiments were undertaken to restore teeth with extensive hard tissue loss, using a carved wooden tooth with an extension into the root canal (336). Pierre Fauchard, the father of modern dentistry, 36  used root canal posts, made of wood, caoutchouc and metal alloys for retaining restorations in severely destroyed teeth (337).  The main indication for using posts was and is to improve the retention of core build-ups or direct and indirect restorations in teeth with compromised or reduced coronal tooth structure (338-341). In the past, posts were also thought to strengthen teeth however, clinical studies led to the suspicion that posts with a high modulus of elasticity, namely metal and ceramic posts, can increase the risk for vertical root fractures (342-347). Therefore, clinical recommendations aim to limit the use of posts to single rooted teeth with considerable reduction of coronal tooth structure, in particular when a ferrule effect of 2 mm depth with a remaining peri-pulpal dentin thickness of 1 mm cannot be achieved after crown preparation (53, 259, 261, 348-352). All other teeth can be usually successfully restored, using adhesively bonded resin composite build-ups with 1-3 mm deep extension into the root canal orifice (259, 261, 349-352). However, decisions should be made on a case-to-case basis.  Interestingly, when using adhesively luted, prefabricated or individually made fiber-reinforced composite posts, with a modulus of elasticity close to dentin, there is increasing evidence that these material combinations can significantly strengthen immature teeth after endodontic treatment (43, 269, 353-356) (Figure 17, p. 37).  37   Figure 17. FRC-post reinforcement of the endodontically treated tooth 11 with thin root canal walls and significant coronal tooth structure loss. The patient presented with pulp necrosis and symptomatic apical periodontitis. Teeth 11 and 21 suffered from a lateral dislocation due to a bike accident. Root canal treatment was performed on tooth 11, followed by root canal filling with gutta percha to mid-root. The remaining canal space was filled with bonded dual-cured composite and an incongruently fitting FRC-post to reinforce the tooth and to improve the retention of the esthetic composite built-up. The tooth was then built-up with a direct, layered restoration, using an esthetic resin composite (Figure 13, p. 27). (Reprinted with permission of John Whiley and Sons (52))  2.2.1.4.1 Fabrication Posts can be custom-made or used in a prefabricated form. Individual resin-reinforced posts can be manufactured chair-side (i.e. Quartz Splint™ RTD; 38  everStick®Post, GC Europe, Leuven, Belgium), while individual cast-metal posts need to be manufactured in a dental laboratory. Prefabricated posts (metal, ceramic, fiber-reinforced composite) are usually part of a system that consists of form-congruent post cavity drills and the respective posts - in different sizes - to accommodate almost all clinical situations. However, commercially available posts are usually smaller in diameter than the root canal of endodontically treated immature teeth (Figure 18, p. 38).   Figure 18. Illustration of the root canal diameter of mature and immature teeth in relation to conventionally available post systems.   39  2.2.1.4.2 Material  Posts can be composed of precious or non-precious metal alloys (i.e. gold, titanium, stainless steel), ceramic (i.e. aluminum oxide, zirconium oxide) or fiber-reinforced composite material (i.e. quartz-, glass- or carbon fibers). Conventionally cemented metal posts were successfully used for decades to restore severely destroyed teeth (61, 62, 357). In the late 1970’s, conventionally and adhesively luted ceramic posts were introduced to improve the esthetical appearance, especially in the anterior region (358-361). A precondition, to achieve sufficient retention with conventionally luted metal or ceramic posts, is a congruent post fit to improve friction between the post cavity wall, the luting cement and the post, which usually requires the preparation of a standardized post cavity. The removal of root canal wall dentin during post cavity preparation and the high modulus of elasticity of rigid metal (53-194 GPa) (362, 363), ceramic (65-265 GPa) (364, 365) and carbon fiber posts (9-117 GPa) (362, 363, 366) are suspected to contribute to the development of vertical root fractures. Fiber-reinforced composite posts (FRC-posts) consist of longitudinal quartz, glass or carbon fibers, an organic resin matrix (i.e. epoxy resin, methacrylate, Bis-GMA) and a coupling agent (silane) to ensure chemical bonding between the fibers and the resin matrix. The quality and mechanical properties (i.e. fracture resistance, cyclic fatigue) of commercially available FRC-posts differ considerably (362, 363, 366, 367) and are amongst others influenced by the: i. silanization technique, ii. amount of fibers, iii. ratio of fiber to matrix and iv. homogeneity of the matrix. The modulus of elasticity of FRC-posts (28-56 GPa) (362, 363, 366, 367) is comparable to 40  dentin (13-18 GPa) (362, 368). FRC-posts are usually adhesively luted to the root canal dentin with resin cement systems. Some authors propose that adhesive bonding of FRC-posts to the root dentin could generate a stable “monoblock” between the three components (369, 370).  2.2.1.4.3 Design Prefabricated posts are available in different geometries (i.e. parallel, conical, double-tapered) and have either a smooth surface or surface retentions (i.e. perpendicular or oblique retention groves, cross-cut relief, screw-type retentions) (371-376). Parallel posts can achieve higher friction for retention, compared to tapered posts however; the tooth structure is considerably weakened by the post space preparation in the apical area where the root becomes narrower. To overcome this problem, double-tapered posts were introduced with a conical apical part and a more parallel part for the middle and coronal root canal areas. Individual posts can be adjusted to the existing root canal anatomy.   2.2.1.4.4 Surface Conditioning Clinical studies show that retention loss of the post is one of the main reasons for failure in post-retained restoration (346, 377-381). When evaluating the failure mode more detailed in vitro, the main failure was often found between the post and the luting system in conventionally and adhesively luted FRC-posts (52, 56, 59). The shape of commercially, prefabricated FRC-posts is milled from a work piece, consisting of embedded fibers in a polymerized matrix with a high conversion rate. 41  Therefore, the resin component of the post surface does not contain a considerable amount of reactive double bonds, required for chemical bonding of the resin-based luting material (52, 56). Different surface conditioning methods have been recommended to increase bonding between the post surface and luting system. Conditioning methods aim to improve: i) mechanical linking by increasing the surface area with macro-retentions (i.e. surface groves, reliefs) or micro-retentions (i.e. sandblasting, etching) (52, 56, 382-385), ii) wettability of the post surface (i.e. degreasing with ethanol or chloroform, silanization, pretreating the surface with the respective adhesive) (52, 386) or iii) chemical adhesive bonding to the resin matrix (i.e. silicatization and silanization) or to the quartz or glass fibers (i.e. silanization) (383, 384, 387-391).   2.2.1.5 Luting Systems Different luting systems are available to bond posts and other reinforcement materials to the root canal dentin. They can be subdivided in conventional, cement-based materials (i.e. zinc phosphate cement, glass ionomer cement) or adhesive luting systems with resin-based cements (i.e. Bis-GMA, TEGDMA, UDMA). Conventional luting systems support the mechanical retention of posts in the root canal mainly by friction, and are predominantly used when inserting metal or zirconium ceramic posts. Adhesive luting systems can bond chemo-mechanically to root canal dentin and pretreated post surfaces, and are recommended for inserting FRC-posts however; they can also be used for metal and ceramic posts.  42  2.2.1.5.1 Conventional Luting Systems  For decades, zinc phosphate and glass ionomer cements were the materials of choice for luting indirect restorations and posts, achieving good clinical long-term results (392-395).  Zinc phosphate cement, consisting of fluid and powder, is easy to handle, cost-effective and relatively technique-insensitive. The solubility, the lack of chemical adhesion to dental tooth structure and the inability to provide a bacterial tight seal can be considered as a disadvantage (396-398).  Glass ionomer cement is mixed from fluid and powder and is often packaged as a capsule material for accurate dosage of the components. Advantages are: i. the ability to chemically bind to calcium ions in dental hard tissues, ii. fluoride release and iii. increased fracture resistance, compared to zinc phosphate cement. The initial sensitivity against moisture and desiccation, during the setting reaction, impairs the handling properties and increases the technique sensitivity (394, 397, 399).  Resin-reinforced glass ionomer cement was introduced in the 1990s to combine the advantages of regular glass ionomer cement (i.e. bonding to tooth structure, fluoride release) with improved mechanical properties by adding a resin composite component. The increased water absorption, resulting in considerable expansion, can be regarded as a disadvantage (397, 400).   2.2.1.5.2 Adhesive Luting Systems  Adhesive luting systems can be, among others, categorized by the dentin conditioning procedure or by their curing mode.  43  In order to achieve a chemo-mechanical bonding of the hydrophobic resin luting cement to the dentin, conditioning of the hydrophilic substrate is indicated. In general, the first step consists of etching of the dentin surface to either remove or dissolve the smear layer and to expose the superficial dentinal collagen network. In a second step, the exposed hydrophilic collagen fibers are coated with an amphiphilic monomer to achieve a more hydrophobic surface. Then, an unfilled resin is applied to attach to the hydrophobic part of the amphiphilic monomer and to infiltrate the collagen network. Depending on the adhesive luting system, these procedures are carried out in separate steps, as described above, or some steps can be combined. Adhesive luting systems can therefore be subdivided in: i. Etch & Rinse adhesives with resin cement, ii. self-conditioning adhesive with resin cement and iii. self-conditioning resin cement (401-408) (Table 6, p. 209). The manufactures are following the request of the dental community to develop simplified systems, in order to reduce the steps for dentin conditioning and luting. However, the performance of simplified materials is often inferior, compared to multistep materials (52, 56, 409, 410). Another feature to characterize luting systems, is the curing mode of the adhesive system and the resin cement (light-, dual- or chemical-cured). Light-curing systems have a limited indication, when luting non-translucent restorations or posts because the light cannot reach the adhesive system and luting cement sufficiently to initiate the polymerization, resulting in reduced bonding properties (314, 411-414). However, some high quality systems consist of a light-curing adhesive, which is cured, before inserting the restoration or post with a dual-cured material (52, 56). 44  Dual- and chemical curing adhesives and resin cements are usually recommended for inserting non-translucent restorations or posts to ensure complete curing in all areas under the restoration or over the entire length of the post cavity (53, 348, 415-417).  2.2.2 Luting of Posts to the Root Canal System 2.2.2.1 Factors Influencing the Bonding Properties of Root Canal Posts  Luting posts to a post cavity is a complex procedure with multiple influencing factors. The influencing factors can be subdivided in six main categories: i. bonding substrate, ii. post system, iii. luting system, iv. application/insertion technique, v. aging and vi. testing method. When luting posts, the root canal dentin is considered to be the only relevant bonding substrate. Bonding to root canal dentin, especially with adhesive luting systems, achieves inferior bonding results, compared to coronal dentin because of the high density of dentinal tubules and the small amount of intra-tubular dentin (418). The type of dentin substrate (i.e. human, bovine) can have a significant influence on the bonding properties, especially when testing multi-step adhesives (348, 370, 418-420). Contamination of the dentinal surface of the post cavity with irrigation solutions (i.e. sodium hypochlorite) (421-423), root canal sealers (424-426) or gutta percha (427, 428) can lead to reduced bonding properties, while final irrigation with chlorhexidine can improve the bonding (60, 429, 430). The localization within the root canal also influences the bonding properties (314, 431-433). 45  Post-specific properties, such as post material (i.e. metal, ceramic, FRC) (434), post fabrication (i.e. prefabricated, individually fabricated) (435), post length (433, 436), post size (432, 437), post fit (438-443), surface relief (i.e. smooth, macro-retentions) (56, 436, 444, 445), surface roughness (382, 446-448) and surface pretreatment (i.e. sandblasting, etching, silicatization, silanization, adhesive application) (52, 449-455) can influence the bonding. The luting system category (i.e. conventional, adhesive) (52, 56, 382, 437, 456), the luting system type (i.e. Etch& Rinse multi-step adhesive with resin cement, self-conditioning adhesive with resin cement, self-conditioning resin cement, resin-reinforced glass ionomer cement, conventional glass ionomer cement) (52, 56, 382, 437, 456), the individual selection within a luting system type (52, 56, 457), the curing mode (light-, dual, chemical-cured) (256, 314, 381) and the chemical composition of the luting system within a luting system type (52, 56, 314, 458) was shown to influence the bonding properties. The application technique of adhesives (i.e. brush types, paper points) and the resin cement (i.e. Lentulo spiral, application on the post, root canal tips) as well as the post insertion technique are also considered to have an influence on the bonding properties (57, 459, 460). In vitro, different methods can be applied to simulate aging under clinical conditions (i.e. thermal cycling, long-term storage in fluids, chewing simulation). Aging usually influences the bonding properties but the effect depends on the duration and the applied aging method (435, 461-465). 46  The methods for evaluating bonding properties can be selected, based on the research question (i.e. pull-out test, push-out test, micro-tensile test, cyclic fatigue testing), and the results usually vary, depending on the applied test method (52, 56, 382, 431, 437, 440, 449, 456, 466-472).  2.2.2.2 In vivo evaluation of the Bonding Properties of Root Canal Posts Clinical studies are considered the gold standard for evaluating the performance and long-term outcome of posts, used to retain coronal restorations in endodontically treated teeth however, high quality studies are scarce (43, 61, 62, 346, 357, 377, 380, 473-478). The quality of these studies is influenced by attributes such as: i. observation period (i.e. short-term, long-term), ii. drop-out rate, iii. study design (i.e. prospective, retrospective), iv. presence of a control group and v. randomization (i.e. randomized, non-randomized, blinded, non-blinded) (98, 479, 480). Compared to in vitro studies, clinical studies have the advantage that multifactorial influence of naturally occurring factors on the outcome can be observed. The identification of a single factor for success or failure is difficult because co-factors cannot be eliminated, as it is possible in laboratory in vitro or ex vivo studies.  The following outcome parameters can be assessed in clinical studies:  Tooth and cumulative survival (i.e. time, rate) (61, 62, 342, 346, 357, 377, 379, 380, 473-478, 481),  Annual or total failure rate (378, 475, 482),  Failure type  Root fracture (342, 346, 357, 377-380, 473, 474, 477, 482), 47   Post and/or core fracture (61, 378, 380, 473, 475-477, 482),  Endodontic failure (61, 357, 378, 380, 473-477, 482),  Debonding of post and restoration (377-380, 473-476, 481, 482),  Tooth loss or extraction (61, 62, 346, 357, 377, 475),  Decay and or marginal gap formation (61, 357, 378, 482) and /or  Periodontal failure (61, 357, 477). Different influencing factors have been evaluated in clinical studies and can be subdivided in study related, patient-related, tooth-related, restoration-related, post-related and luting-related factors:   Study –related factors  Observation period (61, 62, 346, 357, 377-380, 473-478, 481, 482),  Patient-related factors  Age (377),  Sex (357, 377),  Dentition (i.e. fully/partially dentate, absence/presence of adjacent teeth) (62, 482),  Para-functional habits (482),  Tooth-related factors  Tooth type (incisors, canines, premolars, molars) (61, 62, 377, 378, 475, 482) and location (maxilla, mandible) (61, 357),  Periodontal status (357),  Residual coronal tooth structure (346, 377, 473-475, 478), 48   Restoration-related factors   Type of restoration (i.e. direct restoration, crown, double crown, bridge, partial removable denture) (62, 357),  Core type and core build-up material (377, 474),  Ferrule effect (378, 473),  Post-related factors  Post material (i.e. metal, ceramic, FRC) (346, 379, 380, 477, 481),  Post shape (i.e. parallel, tapered) (476),  Post surface design (i.e. smooth, macro-retentive groves, screw-type) (346),  Post fabrication (i.e. prefabricated, individual chair-side, custom-cast) (61, 473) and/or  Luting-related factors (474, 482). All above-mentioned studies were carried out on mature teeth. In vivo studies on the clinical performance of orthograde root canal posts, used in immature endodontically treated teeth, are not available.   2.2.2.3 In vitro evaluation of the Bonding Properties of Root Canal Posts In vitro testing is an important part of the preclinical evaluation of new materials and methods. Other than in vivo studies, laboratory experiments allow to reduce the number of influencing factors, found in a clinical multifactorial scenario. Standardized laboratory conditions allow to focus on the influence of specifically defined factors on the bonding properties of root canal posts. 49  2.2.2.3.1 Interface Inserting posts into the post cavity of endodontically treated teeth with a luting system results in two bonding interfaces; namely the interface between the post and the luting system and the interface between the root canal dentin and the luting system (52, 56, 348, 370, 419) (Figure 19, p. 49).    Figure 19. Overview for the components and interfaces, involved in the adhesion of a luted post to root canal dentin. A - Vertical cut through a root with a luted post; B - Horizontal cut through a root with a luted post; D_LS = Interface between dentin and luting system; LS_P = Interface between luting system and post; P = Post; LS = Luting system; D = Dentin  50  In vitro testing of the bonding properties can focus on the different interfaces. For testing bonding of the luting material to the post, luting system-post samples are prepared to assess i.e. the influence of surface pretreatment or the influence of luting material selection (52, 448, 483-486). To evaluate the bonding of the luting material to the root canal dentin, the preparation of luting material-dentin samples is indicated (487-489). The preparation of tooth-post-luting material samples allows the evaluation of the bonding between the luting material and the post as well as the root canal dentin, under simulated clinical conditions (52, 56, 314, 381, 382, 386, 435-437, 449, 456).  2.2.2.3.2 Dentin Substrate Human extracted teeth are considered the gold standard as a substrate, when testing bonding properties in vitro. However, collecting single rooted teeth in sufficient numbers can be challenging. In addition, a wide variety in human tooth samples is found because (i. different tooth types, ii. age of the donors, iii. tooth and root anatomy and iv. degree of destruction with possible structural changes in the dentin) (52, 490, 491).  Therefore, the substitution of human teeth with animal teeth, as dentin substrate, can be an alternative. Animal teeth are readily available as waste products from slaughterhouses. The teeth are decay-free, usually originate from animals within the same age range and the tooth type can be clearly standardized. Since animal teeth are available in large amounts, the storage interval between tooth extraction and experimental use is usually shorter for animal than for human teeth. Considering 51  this information, it can be stated that the amount of influencing factors on the substrate quality is considerably lower in animal teeth, compared to human teeth (52, 56). Bovine teeth are the predominant substitute for human teeth when testing bonding properties of root canal posts in vitro (52, 56, 433, 460, 492, 493). However, comparative evaluations on the suitability of bovine dentin are scarce (456, 490, 491, 494-502). Studies, comparing structural properties or bonding properties of human and bovine dentin, usually focus on coronal dentin and the results are controversial (491, 495-498). The following results are extracted from the literature (Table 3, p. 51):  Table 3. Comparison of different structural and bonding properties of human and bovine coronal dentin, based on the availabe literature. B = Bovine dentin, H = Human dentin, H2O = Water, SCA = Self-conditioning adhesive, E&RA = Etch & Rinse adhesive, * = statistically significant difference, = no statistically significant difference   Criteria Comparison Reference Tubule Size B > H (*) B > H () Lopes et al. (2009) (496) Schilke et al. (2000) (499) Tubule Density B > H (*) Schilke et al. (2000) (499) Tubules/mm2 H > B (*) H < B () Lopes et al. (2009) (496) Schilke et al (2000) (499) Radiodensity H > B () Fonseca et al. (2004) (494) Hydraulic Conduction B > H () Schmalz et al. (2001) (500) Diffusional H2O Flux B > H () Schmalz et al. (2001) (500) Shear Strength  SCA B > H () Rüttermann et al. (2013) (497) Lopes et al. (2003) (495) E&RA B > H (*) Rüttermann et al. (2013) (497) Lopes et al. (2003) (495)  Only two studies, comparing the bonding properties of FRC-posts to bovine and human root canal dentin, are available (456, 501). In the first study, only one 52  luting system (self-conditioning adhesive with resin cement) was tested, resulting in significantly higher bond strength for human teeth, compared to bovine teeth (501). In the second study, no significant differences in bond strength were found for human and bovine teeth, when luting posts with resin-reinforced glass ionomer cement and self-conditioning resin cement. However, significantly higher bond strengths were found when luting posts adhesively (self-conditioning adhesive and resin cement or Etch & Rinse adhesive with resin cement) to bovine root canal dentin, when compared to human teeth (456). Based on these limited information, the use of bovine teeth to substitute human teeth, especially when testing the bonding properties of root canal post, can be discussed controversially. From a practical point of view, the above-listed advantages of bovine teeth support their use as a substitute. However, care need to be taken when interpreting the results (52, 56).  2.2.2.3.3 Storage of Teeth Storage of teeth between extraction and conduction of the experiments is often necessary. The storage method or storage solution should achieve predictable infection control to avoid cross-contamination (502-504). In addition, the dentin properties should ideally remain unchanged. The findings in the literature are in some instances controversial however, five main influencing factors of storage on the dentin properties have been identified: i. storage time (502, 505-508), ii. storage method (504), iii. storage medium (502-504, 506, 508-510), iv. storage temperature (502, 507) and v. disinfection/sterilization procedure (503).  53   The following guidelines, regarding the storage of teeth or dentin samples, can be proposed:   The storage time should be short and not exceed 6 month (502, 505, 507).  Freezing teeth is preferred over storage in disinfecting solutions, when long-term storage is necessary (504, 511-513).  Storage media can have a significant influence on dentin properties, especially bonding properties (503, 504, 506, 510). Formalin, ethanol, thymol, sodium chloride solution and higher concentrated sodium hypochlorite (3 – 6%) cannot be recommended (502-504, 506, 510). Storage in chloramine-T solution (0.5 – 1.0%) is recommended in a task force report and is widely used (acceptable infection control, none or minimal alteration of the dentin properties) (502).   The samples should be stored at low temperatures to reduce alterations of the dentin properties over time (502).  The use of non-solution sterilization methods (i.e. steam autoclave, chemical heat sterilization, dry heat sterilization, ethylene dioxide, gamma radiation) is controversial because some studies report alterations in the dentin properties, while others did not find significant changes (504, 511-513).   2.2.2.3.4 Methods To assess the bonding properties of conventionally or adhesively luted posts to root canal dentin, different laboratory test are available (514-516), and the results can be reported as dislodgement force in N or as area-dependent bond strength in MPa. The laboratory testing results cannot be directly transferred to the clinical situation 54  and should be interpreted with caution. However, these tests are valuable during the preclinical testing phase of new materials or techniques to avoid in vivo application of low performance methods, possibly resulting in catastrophic failure (515-517). Studies, evaluating the correlation between in vitro results and clinical performance of conventionally and adhesively luted posts do not exist.  Laboratory test, assessing the bond strength or dislodgement force of root canal posts can be categorized as shear bond strength test (i.e. pull-out test, push-out test) (514, 516, 518-520) or tensile tests (i.e. micro-tensile test) (402, 444, 514, 519, 520). All tests have certain advantages and disadvantages and the test selection should be based on the research question and study design.  Pull-out test The sample preparation and testing procedure for pull-out tests is relatively easy and time effective, leading to reproducible results with small variations (52, 56, 518, 519) (Figure 20, p. 55). However, careful alignment of the post with the root canal axis, during luting, embedding and pull-out testing, is crucial to avoid erroneously high and varying results (52, 56).  Advantageous, when using the pull-out test design, is the possibility to evaluate influencing factors, such as: i. post surface design, ii. post size, iii. post length and iv. post shape, over the entire post/post cavity length (56, 382, 433, 436, 437, 445, 521).  The following points could be regarded as disadvantages, when applying this method: i. non-uniform stress distribution, ii. possible jamming of luting system 55  fragments in the gap between the post and the cavity wall, leading to increased friction during the pull-out procedure and iii. the influence of crack propagation, possibly leading to premature failure and lower bond strength values, compared to testing procedures, using thin (i.e. thin slice push-out test) or small samples (i.e. micro-tensile test). Another argument, limiting the application of the push-out test procedure is that pull-out forces are rarely applied under clinical condition, except in abutment teeth for removable dentures (i.e. double crown, prefabricated ball abutments, clasps).   Figure 20. Pull-out test design. The embedded pull-out sample, with the coronally protruding post part, is clamped into the drill chuck of the testing machine to assess the pull-out force, needed to disloge the luted post.    56  Push-out test The push-out test can be categorized as thin-slice (test slice thickness ≤ 1 mm) or thick-slice (test slice thickness > 1 mm) push-out test (514) (Figure 21, p. 57).  Thick slice push-out tests carry the same disadvantages as pull-out tests (i.e. non-uniform stress distribution, possible jamming of luting system fragments in the gap between the post and the cavity wall, influence of crack propagation, non-axial loading) (52, 514). Another factor is the possibly insufficient force application with the push-out plunger in thick samples with high bond strength because the diameter of the plunger is limited to a size slightly below the post diameter and can bend or break, during the force application. These disadvantages can be overcome, when preparing test samples with a slice thickness equal or less than one millimeter. The advantage is that influencing factors, such as luting system, post system or post surface pretreatment can be evaluated and regional differences in bonding properties within the root canal can be assessed (52, 314, 431, 514, 522). However, the time-consuming and technique-intense sample preparation can be considered a disadvantage (52, 514). In addition, when testing posts with inferior mechanical properties (i.e. insufficient silanization of the fibers, leading to insufficient bonding between the fibers and the post matrix), failure within the post can alter the results (381, 523, 524). When testing influencing factors, which require the evaluation over the entire post/post cavity length (i.e. post surface design, post length, post diameter), thin slice push out testing is not indicated (52, 56).  57   Figure 21. Push-out test design. The embedded push-out sample is placed with the larger post diamter down on the holder. The plunger, mounted to the testing machine, moves downwards, until post-dislogement.  Micro-tensile test The micro-tensile test can be subdivided, based on the sample shape (hour-glass or beam shape) (402, 514, 525) (Figure 22, p. 58 and Figure 23, p. 58). Advantageous is the possibility to test pure bond strength with a relatively uniform stress distribution and eliminating the influence of friction, (514, 518, 519). However, sample preparation and testing procedure are time-consuming, technique-intense and sensitive. Depending on the bonding properties of the luting materials, a high pre-testing failure occurs during sample preparation, resulting in considerable loss of samples and possible adulteration of the overall results (514, 518, 519, 525). Therefore, the method is not indicated when testing luting materials with low bond strength, and has limited value when assessing bonding properties of posts.  58   Figure 22. Micro-tensile test design with beam-shaped samples. The beam-shaped micro-tensile sample is attached to the jig with adhesive wax. The upper part of the machine moves upwards, until failure within the components or interfaces occurs.   Figure 23. Micro-tensile test design with hourglass-shaped samples. The hourglass-shaped micro-tensile sample is attached to the jig with adhesive wax. The upper part of the machine moves upwards, until failure within the components or interfaces occurs.  59  Aging Aging procedures, before testing the bonding properties, can improve the predictable value of the results to provide more clinically relevant information (514, 526). Different methods have been used, when testing the bonding performance of posts, luted to root canal dentin, such as: fluid storage (462, 464, 527, 528), thermal cycling (435, 463, 529-532), cyclic mechanical loading (chewing simulation) (463, 531) or a combination of the latter two methods (463, 467).  Failure mode analysis After bond strength testing, failure mode analysis of the samples under the microscope aims to identify the weakest interface or component of the tooth-luting system-post compound. This information can help to improve the overall bonding properties by modifying the luting method or material. The failure mode can be described in a simplified way as: i. adhesive (between bonding interfaces), ii. cohesive (within a substrate or material) or iii. mixed failure, without specifying the involved bonding interfaces or substrates/materials (431, 523, 533-536). This description is not sufficient to identify the specific site of failure for future improvement of the bonding properties. When luting posts to root canal cavities, two bonding interfaces, where adhesive failure can occur, are generated; namely the interface between the cavity wall dentin and the luting system and the interface between the between the post surface and the luting system. In addition, failure can occur within the canal wall dentin, the luting material and the post material (52, 56, 370, 537, 538) (Figure 19, p. 49). The latter three failure modes are often defined as cohesive failure. 60  However, luting materials (i.e. glass ionomer cement, resin composite cement) and reinforcement or post materials (i.e. fiber-reinforced composite) are usually compositions of different materials and the failure occurs between the components of these materials. Therefore, failure within these materials should not be considered cohesive failure but adhesive failure. To avoid confusion with the nomenclature, report of failure may only describe the involved interfaces or substrates/materials (i.e. failure within dentin, failure between dentin and luting system, failure within luting system, failure between luting system and post, failure within post) (52, 56).  61  Chapter 3: Aim, Research Questions and Hypotheses In vitro studies provide evidence that reinforcement of endodontically treated immature teeth with fiber-reinforced composite posts can strengthen the fracture prone cervical area. However, little is known about the influence of the post fit on the bonding properties of conventionally and adhesively luted fiber-reinforced composite posts in immature teeth with wide root canals.  3.1 Aim The aim of the study is to evaluate the influence of the post fit (congruent, incongruent) on the pull-out force of conventionally and adhesively luted quartz fiber-reinforced composite posts with a macro-retentive surface design. In addition, the failure mode is assessed, depending on the post fit and the luting material.  3.2 Research Questions 1. Does the post fit, inspective of the luting system, influence the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts? 2. Does the luting system type, irrespective of the post fit, influence the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts? 3. Does an interaction between post fit and luting system type exist, which influences the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts? 62  4. Does the post fit influence the pull-out force and the failure mode of quartz fiber-reinforced composite posts, depending on the luting system type?  3.3 Hypotheses 1. The post fit, irrespectively of the luting system, does not influence the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts. 2. The luting system type, irrespectively of the post fit, does not influence the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts. 3. No interaction between post fit and luting system type exists, which influences the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts. 4. The post fit does not influence the pull-out force and the failure mode of quartz fiber-reinforced composite posts, depending on the luting system type.  63  Chapter 4: Materials and Methods 4.1 Materials 4.1.1 Substrate Bovine deciduous mandibular teeth (Di3) were extracted from slaughtered young bulls with a mean age of 6 month. The extracted teeth were then visually and radiographically evaluated, according to the following defined inclusion criteria:  Completely developed apex without resorptions,  Straight roots over a course of at least 10 mm, apically of the CEJ,   Roots free of decay and cracks or fractures,  Round or slightly oval root canals (oro-buccal to mesio-distal ratio < 2:1). A total of 260 teeth, meeting theses inclusion criteria, were selected for the study. The crowns were removed at the CEJ, followed by removal of soft tissue remnants (PDL, gingiva and pulp). The roots were then stored for a maximum of 2 weeks (Chloramine T 0.5%, 8°-10°C), until used for the experiments.  4.1.2 Post Systems Based on the results from previous experiments (56, 436, 456) the following two post systems were selected for this study:  FRC-post System (Figure 24, p. 64)  Macro-LockTM Post Illusion X-RO (sizes 1, 3 and 6) (RTD, Saint Égrève, France)  Uni-directional silanized quartz fibers embedded in an epoxy-resin matrix 64   Post-specific data (Table 7, p.210)  Figure 24. Macro-Lock Post Illusion with indications for diameters D1 and D2 Post size 1: D1 = 0.80 mm, D2 = 1.35 mm; Post size 3: D1 = 1.00 mm, D2 = 1.67 mm; Post size 6: D1 = 1.30 mm, D2 = 2.22 mm  Titanium post system (Figure 25, p. 64)  Custom-made titanium post (size 3) (NTI-Kahla GmbH, Kahla, Germany)  Post-specific data (Table 8, p. 210)  Figure 25. Titanium post with indications for diameters D1 and D2  Post size 3: D1 = 1.10 mm, D2 = 2.20 mm 65  4.1.3 Luting Systems For luting the posts to the dentin substrate, conventional and adhesive luting systems, with different conditioning mechanisms, can be used. Based on the results from previous experiments (52, 56, 314, 382, 386, 436, 437, 449, 456, 467), the luting materials KetacTM Cem Aplicap (3M ESPE, Seefeld, Germany), Fuji PlusTM Capsule (GC Europe, Leuven, Belgium), RelyXTM Unicem Aplicap (3M ESPE, Seefeld, Germany), Multilink® Primer and Multilink Automix (Ivoclar Vivadent, Schaan, Liechtenstein) and LuxaBond® and LuxaCore Z® Dual (DMG, Hamburg, Germany) were selected for this study (Figure 26, p. 68)  KetacTM Cem Aplicap  System component: KetacTM Cem Aplicap  No dentin conditioning   Conventional luting system o Glass ionomer cement o Capsule material containing powder and fluid  Chemical curing mode  Material-specific data (Table 9, p. 211)  Fuji PlusTM Capsule  System components: o Fuji PlusTM Conditioner o Fuji PlusTM Capsule 66   Separate dentin conditioning step  Conventional luting system o Resin-reinforced glass ionomer cement o Capsule material, containing powder and fluid  Chemical curing mode  Material-specific data (Table 10, p. 211)  RelyXTM Unicem Aplicap   System component: o RelyXTM Unicem Aplicap  No separate dentin conditioning step  Adhesive luting system o Self-adhesive resin cement o Capsule material, containing powder and fluid  Dual curing mode  Material-specific data (Table 11, p. 211)  Multilink® Primer and Multilink Automix  System components o Multilink® Primer A and B o Multilink Automix®  Separate dentin conditioning step 67  o One-step self-conditioning adhesive  Adhesive luting material o Resin cement o Automix syringe, containing resin base and catalyst  Dual curing mode  Material-specific data (Table 12, p. 212)  LuxaBond® and LuxaCoreZ® Dual  System components o Etching Gel® o LuxaBond® Prebond o LuxaBond® Primer A and B o LuxaCore Z® Dual  Separate dentin conditioning step o Etch & Rinse two step conditioning adhesive  Adhesive luting material o Resin cement o Smartmix syringe, containing resin base and catalyst  Dual curing mode  Material-specific data (Table 13, p. 212) 68     Figure 26. Luting systems - overview of the conditioning, bonding and luting steps  69  4.2 Methods Figure 27 (p. 69) provides and overview about the tooth and sample preparation, randomization and testing procedure.   Figure 27. Flowchart of the experimental procedure KC = Ketac Cem; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z; TiP = RPR Protptype Titanium Post; MLXRO = Macro-Lock Post Illusion X-RO; C = congruency; MIC = medium incongruency; HIC = high inconruency 70  4.2.1 Sample Preparation and Randomization 4.2.1.1 Tooth Preparation The freshly extracted teeth were immediately stored in Chloramine T 0.5% solution (Chloramine-T trihydrate, Laborbedarf Sachse GmbH, Ulm, Germany) for disinfection and prevention of desiccation during transport. The teeth were then cleaned and the external soft tissue remnants were removed using a hand scaler (AP67CN Petschelt, Deppeler SA, Rolle, Switzerland) followed by polishing with pumice (Sherasept Bims, SHERA Werkstoff-Technologie GmbH & Co. KG, Lemförde, Germany) using a prophylaxis cup (Gummipolierer 6 Lamellen Standard, Möhrle Dental, Neuhausen, Germany) in a straight hand-piece (GENTLEpower LUX 10 LP, KaVo Dental GmbH, Biberach/Riß, Germany). Then, the crowns were removed at the CEJ with a diamond disc (947D, Hager & Meisinger GmbH, Neuss, Germany) in a straight hand-piece, followed by the removal of the pulp with barbed broaches (Sterile Nervnadeln, VDW GmbH, München, Germany). The teeth were then stored for a maximum of 2 weeks in Chloramine T 0.5%, until used for the experiments.  The root canal preparation was carried out immediately before the teeth were used for the experiments. During the glide path preparation to size 02.20 with hand files (Sterile K-Files, VDW GmbH) and enlargement of the root canals with rotary files to size 04.35 (FlexMaster® Instruments and VDW.GOLD RECIPROC motor, VDW), the canals were intermittently irrigated with NaOCl 3% (University Pharmacy, University Erlangen, Germany), followed by a final rinse with citric acid 40% (University Pharmacy) for smear layer removal.   71  4.2.1.2 Embedding of the Roots For embedding the roots, polypropylene molds (Figure 28, p. 71) were individually manufactured by modifying 10 ml syringes (BD Discardit II Syringes 10 ml, Becton Dickinson, Franklin Lakes, USA).   Figure 28. Modified polypropylene mold  For secure placement and parallel alignment of the molds, an individual wooden mold holder (sample holder A) was manufactured in the Dental Workshop (University Erlangen, Germany) (Figure 29 A and B, p. 72). In addition, for parallel alignment of the root canals, during the embedding procedure, a Plexiglas sample holder (Sample holder B), matching the positions of the molds in the mold holder, was manufactured in the Dental Workshop (Figure 30 A and B, p. 72). The holder consisted of a perpendicular extension to be placed in a parallelometer (Parallelometer D-P 26, Harnisch & Reith, Winterbach, Germany) and canals for 72  seating Hedström files (Hedström files size 60, VDW GmbH) to hold and align the roots parallel to the root canal axis, during the embedding procedure.  Figure 29. Wooden holder (sample holder A) for secure placement of five polypropylene molds, perpendicular to the table plane. A - Top view; B - Front view   Figure 30. Plexiglass holder (sample holder B) for secure placement of five root samples along the root canal axis, perpendicular to the table plane. A - Top view; B - Front view  Two grooves (ca. 1.0 - 1.5 mm deep) were placed circumferentially within the coronal 6 mm of the tooth, using a round bur (Steel Bur 1RF 012, Hager & Meisinger GmbH) in a straight hand-piece to ensure secure retention of the roots in the 73  embedding material (Figure 31, p. 73). Before embedding the tooth samples, the root surfaces were dried with air.  Figure 31. Root sample with two circular retention groves within the coronal 6 mm.   The roots were then attached to the sample holder by inserting the Hedström files into the root canals, and the sample holder was inserted into a drill chuck, attached to the parallelometer. Then, the mold holder with the molds was aligned with the roots (Figure 32, p. 74). To embed the roots, the molds, containing the roots, were filled with chemically curing acrylic resin (Technovit 4071, Hereaus Kulzer GmbH, Hanau, Germany), using a 10 ml syringe (BD Discardit II Syringes 10 ml) and a 45° bend tip (Elephant Tip, Transcodent GmbH & Co. KG, Kiel, Germany). After setting of the embedding resin, the samples were removed and stored until further use (deionized water, 8°C, maximum storage time 10 days). 74    Figure 32. Embedding procedure of the root samples.  The polypropylene molds were placed in the wooden holder A (Figure 29 A and B, p. 72), perpendicular to the table plane. Five roots were attached, along their root canal, using Hedström files, protruding from the plexiglass holder B (Figure 30 A and B, p. 72) to ensure parallel allignement with the root canal axis and the molds. The holder B was placed in the drill chuck of the parallelometer, and the samples were lowered into the molds. The mold on the left hand side was filled with embedding resin.  4.2.1.3 Preparation of the Sample Slices and Counterparts The coronal and apical surfaces of the resin-tooth samples were ground flat, perpendicular to the root canal axis, using a model trimmer (HSS-AZ, Wassermann, Wassermann Dental-Maschinen GmbH) and the custom made sample holder C (Dental Workshop, University Erlangen) (Figure 33 A and B, p. 75).  75   Figure 33. Sample holder C A - Front view: The holder was perpendicularily adjusted to the model trimmer base plate as well as to the edge guide. The embedded sample (central) was perpendicularily aligned to the model trimmer disc in all three dimensions with the aid of the holder. B - Side view: The sample was aligned through the sample holder to ensure three-dimensional perpendicular alignement of the sample with the model trimmer. The coronal part of the embedded sample was flat ground, perpendicular to the root canal axis, using a model trimmer with a diamond disc.  Using a circular table saw (Table saw FET, Proxxon, Germany) and the custom-made sample holder D (Dental Workshop, University Erlangen), a 7 mm thick slice was sectioned from the coronal part of the resin-tooth sample, to be used for the experiments (Figure 34 A and B, p. 76). The remaining part of the sample was discarded. The 7 mm thick sample slice was then precision-ground (Phoenix 4000 and silicone carbide wet grinding paper P120, Buehler, Düsseldorf, Germany), perpendicular to the root canal axis to a thickness of 6 mm, using the modified thin-section specimen holder E (Buehler) (Figure 35 A and B, p. 76).  76   Figure 34. Sample holder D A - Front view: Three molds with samples were perpendicularily aligned to the root canal axis through the sample holder. Two slots are empty. B - Side view: The holder with the inserted samples was perpendicularily adjusted to the saw base plate as well as to the edge guide. The embedded sampels were perpendicularily aligned in all three dimension through the holder. A 7 mm thick slice was cut off from the coronal part of the embedded root-resin sample.    Figure 35. Sample holder E A - Bottom view. The three sample slices were perpendicularily adjusted to the root canal axis in the sample holder. The samples were hold in place with a silicone template.  B - Front view. The intended sample hight (6 mm) was adjusted on the sample holder, with the 7 mm thick slices protuding from the holder. The holder rim was made from wolfram carbide to prevent abrasion of the sample holder material, during the grinding procedure.  77  After measuring the sample slice thickness (tolerance 6 mm ± 0.06) with a digital caliper (CD-15CPX, M.A.S. Mess- und Werkzeugtechnik, Lüdenscheid, Germany), three half-round retention grooves were prepared at the apical surface, in the embedding resin, with a tungsten carbide cutter (Orthodontic Instrument HM 251GX, Hager & Meisinger) and a straight hand-piece, defining the sample slice as the ‘female part’ (Figure 36 A and B, p. 77). The sample slices were then stored, until further use (deionized water, 8°C, maximum storage time 10 days).  Figure 36. The 6 mm sample slice consisting of the embedded root segment. A - Bottom view: Three retention groves were prepared in the resin part of the apical surface of the 6 mm sample slice. B - Front view  Before post cavity preparation, a plaster counterpart (‘male part’) was prepared. The plaster (Fujirock EP®, GC Europe) was poured into a modified polypropylene mold (BD Discardit II Syringes 10 ml). The sample slice, with the retention groves facing the plaster, was placed on top of the uncured plaster and then pushed axially into the mold, until the coronal surface of the specimen was leveled with the rim of the mold (Figure 37, p. 78). After the plaster had set, the molds, 78  containing the plaster counterpart and the sample slice, were stored in a wet chamber, until further use (100% humidity, 37°C, maximum storage time 24 hours).   Figure 37. Plaster counterpart preparation. The modified polypropylene molds were placed in sample holder A. The plaster (creamy consistency) was filled into the molds. Then, the sample slices were adjusted on top of the uncured plaster and gently pushed into the mold. To level the upper surface with the rim of the mold, a flat rubber stamp was used. The plaster excess was able to exit through previously prepared holes on the base of the suringe plunger.   4.2.1.4 Group Distribution and Randomization The size 1, 3 and 6 (Figure 24, p. 64) represent high incongruent (HIC), medium incongruent (MIC) and congruent (C) post fit, respectively (Figure 38, p. 79).  79   Figure 38. Post fit for the FRC-posts, depending on the cavity and post size.  Conguency (C) = Post cavaity size 6 and post size 6; Medium incongrunecy (MIC) =  Post cavity size 6 and post size 3; High incongruency (HIC) = Post cavity size 6 and post size 1; ER = Embedding resin; D = Dentin; A = Adhesive; LS = Luting system; P = Post  The FRC-posts were combined with four luting systems (Fuji Plus, RelyX Unicem, Multilink Primer/Multilink and LuxaBond and LuxaCore Z), which resulted in 12 test groups. For the control group, a titanium post with a congruent fit (Figure 25, p. 64) was combined with the conventional glass ionomer cement Ketac Cem. 260 samples (n = 20 per group) were randomly assigned to the 13 groups (Figure 27, p. 69).     80   4.2.1.5 Post Cavity Preparation            Figure 39. Preparation of the sample for post cavity preparation. After preparing the plaster counterpart, the mold was removed from the holder, and the syringe plunger was replaced with an adjustable resin plug.   The syringe plunger was removed from the mold and replaced with an adjustable resin plug (Figure 39, p. 80). After placing the mold in sample holder C, the specimens were aligned, along the root canal axis, with the pilot bur (0.7 mm HSS Spiral Drill, Isaho Versand e.K., Hohndorf, Germany) in a bench drill (Bench Drill Press TBM115, Proxxon). A pilot cavity (depth 11 mm, diameter 0.7 mm) was drilled into the root canal and the plaster counterpart (Figure 40 A and B, p. 81). Using the bench drill, the pilot cavity was enlarged with post cavity pilot drills (Macro-Lock® Post finishing drills sizes 1, 3 and 6, RTD, Saint Égrève, France and RPR pilot drill 81  size 3, NTI, Kahla, Germany) to the designated post cavity size, according to the group distribution.   Figure 40. Post cavity preparation. The mold, containing the sample slice, the plaser counterpart and the adjustable resin plug (from top to bottom), was adjusted in sample holder C. The root canal was aligned with the drill to prepare the pilot cavity, followed by enlaging the post cavity to the designated cavity size. The cavity was drilled into the root canal (6 mm) and the plaster counterpart (5 mm), resulting in an 11 mm deep cavity.  A - The mold with holder C was aligned with the bur in the bench drill. B - An 11 mm deep cavity was prepared in the root and the plaster counterpart.  The sample slice and plaster counterpart were removed from the mold and gently separated. The sample slice was then placed on a plane-parallel flat holder with a central canal (sample holder F) (Dental Workshop, University Erlangen) to enlarge the post cavity with a post cavity pilot bur (working length 11 mm) to size 6 for 82  the test groups (Macro-Lock Post finishing drill size 6, RTD) and size 3 for the control group (RPR finishing drill size 3, NTI) (Figure 41 A and B, p. 82).  Figure 41. Post cavity enlagement in the sample slice. The separated sample slice was placed on a flat holder (sampel holder F) and the root canal was aligned with the canal in the sample holder. Then, the post cavity was enlaged to size 6 at a depth of 11 mm for the test group (RTD post drill) and to size 3 (NTI post drill) for the control. A - The sample slice with holder F was aligned with the drill in the bench drill. B - An 11 mm deep cavity was prepared in the root.  The sample slices (deionized water, 20 °C, maximum storage time 1 hour) and the plaster counterparts (dry) were then stored individually in Multi-well Plates (24-well plates, BD Falcon, Franklin Lakes, USA), until post insertion.    4.2.1.6 Post Insertion After insulating the upper surface of the plaster counterpart (10% alcoholic curd soap solution), the counterparts were placed in a modified polypropylene mold 83  (BD Discardit II Syringes 10 ml). The root canals of the sample slices were rinsed with de-ionized water and dried. The samples slices were then also placed in the mold and precisely aligned with the previously placed plaster counterpart, by using the retention grooves in the sample slice and the protrusions on the counterpart as a guide. The molds were then secured in sample holder G (Dental Workshop, University Erlangen) (Figure 42, p. 83).  Figure 42. Preparation of the sample for post insertion. The plaster counterpart and the sample slice were placed into the polypropylene mold. Both parts were precisely aligned, using the retention grooves in the sample slice and the protrusions in the plaster counterpart. The molds were then placed in the sample holder G.   The posts were cleaned with 70% alcohol (University Pharmacy) and dried. The dentin of the post cavity and the post surface was prepared, according to the manufacturer’s instructions for the different luting systems (Table 14, p. 213 - Table 18, p. 215). The post cavity in the plaster counterpart and sample slice was completely filled with the respective luting cement, using specific application aids: 84   Ketac Cem: AccuDose® Needle Tubes 20 ga (Centrix, Shelton, USA)  Fuji Plus: AccuDose® Needle Tubes 20 ga (Centrix)  RelyX Unicem: Elongation Tip (3M ESPE)  Multilink: Endotip (Ivoclar Vivadent AG)  LuxaCoreZ: Endotip (DMG) To improve the wetting of the post surface with the luting cement, the posts were rolled in a cement reservoir on a mixing pad, before inserting the posts into the post cavity. The coronal excess luting cement was gently removed with a micro-brush (Benda® Micro Applicators, Centrix), ensuring to avoid a luting material deficit in the gap between post and post cavity. Then, an individually prepared polyethylene foil (Erkodur 0.5 mm, Erkodent, Pfalzgrafenweiler, Germany), followed by a stable plastic disc (Erkodur 2.0 mm, Erkodent) with a fitting central hole, was placed over the post and pressed onto the coronal sample slice surface to push away the remaining cement excess (Figure 43, p. 85). The luting material was cured, according to the manufacturer’s instructions (Table 14, p. 213 - Table 18, p. 215).  After gently removing the plastic disc and the polyethylene foil, the samples were stored with the mold in a wet chamber for initial setting of the luting material (100% humidity, 37°C, dark, 1 hour).  After removing the sample slice together with the plaster counterpart from the mold, the sample slice was gently separated from the plaster counterpart by axially pulling with an extraction forceps (DH702R, Aesculap AG, Tuttlingen Germany), without touching the post (Figure 44, p. 85).  85   Figure 43. Post placement procedure. After the post was inserted and the majority of the excess luting material was removed, a 0.5 mm polyethylen foil with a central hole was placed over the post, followed by a 2 mm plastic disc. The foil was pushed against the coronal sample surface with the plastic disc to squeeze out the remaining excess luting material.    Figure 44. Separation of sample slice and counterpart. The sample slice and plaster counterpart were gently separated by holding the sample slice with extraction forceps and the plaster counterparts with the fingers to apply axial force. 86  The resin-tooth-post samples were then individually stored for 24 hours in Multi-well Plates for standardized setting (deionized water, 37°C, dark), before pull-out testing.  4.2.1.7 Preparation of the Post-Tooth Sample for Pull-out Testing  The apically projecting part of the post was removed with a flexible diamond-coated disc (947D) in a straight hand-piece (Figure 45, p. 86), followed by flat grinding the apical surface by hand with wet grinding paper (Silicon Carbide Paper P240, Buehler) to remove the protruding post remnants (Figure 46, p. 87).   Figure 45. Removal of apical post protrusion.  The protruding apical part of the post was cut off using a diamond-coated disc in a hand-piece.  The samples were then again stored individually in Multi-well Plates until embedding (deionized water, 37°C, dark, maximum storage time 1 hour).  87   Figure 46. Removal of apical post remnants. The apically protruding post remnants were removed by flat grinding the sample manyall, using a wet slilicon cabide paper.  The modified EPDM-molds (15 mm high) (SampleKup, Buehler) were pretreated with a separator (Shera Sepal, Shera, Lemförde, Germany) for easier removal of the embedded samples. The resin-tooth-post samples were placed in the sample holder H (Dental Workshop, University Erlangen) (Figure 47 A and B, p. 88) along the post axis, and then aligned with the EPDM molds by placing the sample holder in a parallelometer (Parallelometer D-P26) (Figure 48, p. 88).   88   Figure 47. Sample holder H for axial alignement of the posts with the parallelomenter  A - Front view; B - Top view   Figure 48. Embedding procedure for pull-out testing. The samples were aligned for embedding, along the post axis, to the EPDM molds using the sampel holder H (Figure 47 A and B, p. 88) and a parallelometer. 89  The molds were filled to 80% with acrylic resin (Technovit 4071) and the sample holder H was lowered axially, until the samples were level with the rim of the molds. Acrylic resin was added to the molds if necessary, ensuring that the coronal surface of the resin-tooth-post samples was not covered with embedding resin. After setting of the embedding resin, the samples were removed from the molds and stored until the pull-out testing procedure (deionized water, 37°C, dark, maximum 1 hour storage time).  4.2.2 Pull-out Testing The samples were secured in a three-jaw drill chuck (Type 136S, Roehm, Sontheim, Germany) by clamping the coronally protruding post part, 2 mm away from the coronal samples surface. Then, the drill chuck was attached to the upper jig part (Dental Workshop, University Erlangen) of the universal testing machine (Zwicki, Zwick, Ulm, Germany), allowing free horizontal movements through a 2D ball bearing. The sample was placed underneath the sample holder of the lower jig part (Dental Workshop, University Erlangen), ensuring that no preload was applied to the sample (Figure 49, p. 90). Using the universal testing machine with the software TestExpert (Zwick, Ulm, Germany), the pull-out force (Fmax) for post dislodgement was assessed (cross-head speed 5mm/min, 2 kN load cell). The pull-out procedure was terminated at 70% of Fmax. After evaluating the force-displacement diagram for possible measuring errors, the maximal pull-out force was recorded in N for each sample, in an individually developed data sheet.  90   Figure 49. Pull-out testing procedure. The post was securely clamped into a three jaw drill chuck. The drill chuck was attached to the upper moving part of the univesal testing machine, allowing free movement over a 2D ball bearing. The embedded sample was placed under the holder, which was attached to the steady, lower part of the testing machine.  After finishing the pull-out testing procedure, the tooth-post samples were removed from the drill chuck and stored in a wet chamber (100% humidity, 22°C, dark, maximum storage time 48 hours), until failure mode analysis was performed.  91  4.2.3 Failure Mode Analysis Using a band saw (MICRO-Band Saw MBS/E, Proxxon), three determined breaking lines were cut into the embedding resin to free the tooth-post samples from the embedding material (Figure 50 A and B, p. 91).   Figure 50. Removal of the embedding resin. A - Embedded tooth-post sample with three predetermined breaking cuts in the acrylic resin;  B - Embedded tooth-post sample, after removing one acrylic resin part  After removing the tooth-post samples from the embedding resin, two longitudinal grooves, on the opposite side of the root, were cut with a diamond disc (947D) and a straight hand-piece as predetermined breaking lines to separate the roots in two halves, by slitting them gently with a plaster knife (HS Gipsmesser Gritmann, Henry Schein, Langen, Germany). The tooth halves and the post were individually stored (Rotilabo Micro-centrifuge Tubes black, Carl Roth GmbH, Karlsruhe, Germany), until failure mode analysis (maximum storage time 1 hour).  The failure mode was evaluated by analyzing booth tooth halves (TH1 and TH2) and the post (P) under a stereomicroscope (Stemi SV 11, Zeiss AG, Jena, Germany).  92  The failure mode was estimated in percentages for the following five categories:  Failure within the dentin (F_D) (%)   Failure between the dentin and luting system (F_D_LS) (%)  Failure within the luting system (F_LS) (%)  Failure between the luting system and post (F_LS_P) (%)  Failure within the post (F_P) (%) The total for each individual part (TH1, TH2 and P) was 100%.  The mean failure mode (Fmean) for each tooth-post sample was calculated, using the following formulas:  Fmean_D = (F_D (TH1) + F_D (TH2) + F_D (P))/3 (%)  Fmean_D_LS = (F_D_LS (TH1) + F_D_LS (TH2) + F_D_LS (P))/3 (%)  Fmean_LS = (F_LS (TH1) + F_LSD (TH2) + F_LS (P))/3 (%)  Fmean_LS_P = (F_LS_P (TH1) + F_LS_P (TH2) + F_LS_P (P))/3 (%)  Fmean_P = (F_P (TH1) + F_P (TH2) + F_P (P))/3 (%) The total for each sample was 100%.      93  4.2.4 Statistical Analysis The statistical analysis (descriptive and comparative) was carried out, using SPSS 20.0 (IBM Corporation, Armonk, USA). The general significance level was set at α = 0.05.   Descriptive Statistics  The data for the pull-out force (Fmax) in N were described by using median, mean, standard deviation, maximum, minimum, inter-quartile range, variance and co-factor of variation (standard deviation/mean*100). The failure mode analysis in percentage was reported by using mean and standard deviation.  Diagrams The pull-out force was displayed graphically, using box plots. The results of the failure mode analysis were shown in stacked bar charts.  Test for Normal Distribution The Kolmogorov-Smirnov test (539) is a non-parametric test, which was used to test the pull-out force data in terms of normal distribution. P-values > 0.05 indicated normal distribution of the data, within a specific group.  For data showing normal distribution, parametric tests were applied for comparative statistics, while non-parametric tests were used for non-normally distributed data.   94  Test for Equality of Variances  The Levene test (540) is an inferential statistical test and was used to evaluate the equality of variances for two or more groups, as a precondition, before comparing test results. P-values > 0.05 indicated equality of variances for the tested group data. The result of the Levene test was taken into consideration when interpreting results of the comparative tests and for selecting the post-hoc tests.   Test for Significance of the Influencing Factors Based on the findings of the Kolmogorov-Smirnov test, the parametric Two-way ANOVA (541) was applied to test if the factors post fit, luting system selection and the interaction of the two factors were significantly influencing the pull-out force. Since homogeneity of variances was not found with the Levene test, the local significance level was adjusted for secure interpretation of the Two-ay ANOVA results to α’ = 0.001.  Test for Pairwise Comparison (Post-hoc Tests) Based on the findings of the Kolmogorov-Smirnov test and the Levene test, the parametric Dunnett T3 test (542) was used for pairwise comparison of the pull-out force between two groups. In cases of multiple pairwise comparisons, the Bonferroni correction procedure (543) was applied to offset the α-error accumulation by adjusting the local significance level to α’ (α’ = α /number of comparisons). 95  Chapter 5: Results 5.1 Influencing Factors In this study, the influence of the factors post fit and luting system, as well as the interaction between the two factors on the pull-out force was tested with Two-way ANOVA. As a precondition, the data per group should be normally distributed and the variances should be equal.  5.1.1 Test for Preconditions for Two-way ANOVA 5.1.1.1 Test for Normal Distribution of the Pull-out Force Data Pull-out force data (N) were tested for normal distribution, using the Kolmogorov-Smirnov test (Table 19, p. 216 - Table 21, p. 216). All data were normally distributed (p > 0.05) and the precondition for using Two-way ANOVA was fulfilled.  5.1.1.2  Test for Equality of Variances of the Pull-out Force Data For testing the pull-out force data of equality of variances, the Levene test was used. The p-value was less than 0.001, which represents not equal variances. Therefore, the local significance level was adjusted to α’ = 0.001 to offset possible errors when interpreting the results of the Two-way ANOVA.  5.1.2 Test for General Significance of the Influencing Factors The post fit and the luting system influenced the pull-out forces significantly (Two-way ANOVA, p < 0.001). The interaction of the post fit and the luting system did not significantly influence the pull-out forces (p = 0.030). 96  5.1.2.1 Influencing Factor Post Fit The descriptive data for the pull-out force and the failure mode analysis were presented in Table 22 (p. 217) and Table 23 (p. 217).   Figure 51. Pull-out forces (N), subdivided by post fit and in relation with the control. Two-way ANOVA revealed a significant influence of the post fit on the pull-out force. Post-hoc testing (Dunnett T3 test) showed no significant differences between medium and high incongrency at the local significance level (α’ = 0.017). Co = control; C = Congruency; MIC = Medium incongruency; HIC = High incongruency; = no statistically significant difference  For pairwise comparison, the Dunnett T3 test was used (Table 24, p. 217), and the local significance level was adjusted with the Bonferroni correction procedure (α’ = α/3 = 0.017). The highest pull-out force was found for the group with the congruent post fit (436.6 ±148.7 N), which was significantly higher than the pull-out forces for medium (426.0 ±102.1 N; Dunnett T3, p < 0.017) and high incongruent post fit (397.5 97  ±89.8 N; Dunnett T3, p < 0.017). All test groups achieved significantly higher pull-out forces than the control (207.2 ±35.1 N, Dunnett T3, p < 0.017) (Figure 51, p. 96).  Figure 52. Failure mode (%), subdivided by post fit. C = Congruency; MIC = Medium incongruency; HIC = High incongruency; F_D = Failure within dentin; F_D_LS = Failure between dentin and luting system; F_LS = Failure within luting system; F_LS_P = Failure between luting system and post; F_P = Failure within post   The main failure for all three groups was found between the dentin and the luting system (congruency 64.2%, medium incongruency 70.7%, high incongruency 65.8%), followed by failure between the luting system and the post (congruency 35.5%, medium incongruency 29.3%, high incongruency 34.2%). Failure within the luting system and within the post was only found for the congruent post fit (Table 23, p. 217, Figure 52, p. 97).  98  5.1.2.2 Influencing Factor Luting System  Figure 53. Pull-out forces (N), subdivided by luting system and in relation with the control. Two-way ANOVA revealed a significant influence of the luting system on the pull-out force. Post-hoc testing (Dunnett T3) showed no significant differences between RXU and MLP_ML at α’ = 0.008. Co = control, FP = Fuji Plus, RXU = RelyX Unicem; MLP_ML = Multilik Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z; = no statistically significant difference  The highest pull-out force was achieved using LuxaBond/LuxaCore Z (544.0 ±96.6 N) followed by Fuji Plus (441.2 ±44.9 N), RelyX Unicem (390.7 ±80.5 N) and Multilink Primer/Multilink (379.3 ±106.8 N) (Table 25, p. 218, Figure 53, p. 98). Pairwise comparisons were interpreted at an adjusted local significance level (α’ = α/6 = 0.008). Pairwise comparison (Table 27, p. 218) of all groups revealed statistically significant differences (Dunnett T3, p < 0.008), except when comparing RelyX Unicem and Multilink Primer/Multilink (Dunnett T3, p = 1.000). All test groups 99  achieved significantly higher pull-out forces than the control group (207.2 ±35.1 N, Dunnett T3, p < 0.008).  Figure 54. Failure mode (%), subdivided by luting system. FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilik Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z; F_D = Failure within dentin; F_D_LS = Failure between dentin and luting system; F_LS = Failure within luting system; F_LS_P = Failure between luting system and post; F_P = Failure within post   The main failure for Rely X Unicem, Multilink Primer/Multilink was found between dentin and luting system while the main failure for Fuji Plus occurred between post and luting system (Table 26, p. 218, Figure 54, p. 99) LuxaBond/LuxaCore Z showed mixed failure between dentin and luting system and 100  between post and luting system. The SEM images (Figure 55, p. 100 - Figure 57, p. 102) show the representative failure modes between: i. post and luting system, ii. dentin and luting system and iii. dentin and luting system and post and luting system.  Figure 55. SEM images of predominant failure between post and luting system. The sample is characteristic for Fuji Plus, with cement remaining on the root canal wall and exposure of the post surface. The cracks in the luting material are drying artifacts.  A - Tooth half: The root canal wall is covered to 80 % with luting material, showing the indentations of the post surface. Root canal dentin (20%) is exposed in the upper left area (arrow).  B - Post: The post surface is exposed (80%), showing the spiral-shaped macro-retentions and the longitudinally oriented fibers. Remaining luting material (20%) covers the center of the post.  C - Tooth half: Magnification of the boxed area in picture A, showing the exposed dentin surface (left) and luting material covering the dentin (right), with indentations of the post fibers. 101   Figure 56. SEM images of predominant failure between dentin and luting system. The sample is characteristic for Relx X Unicem and Multilink Primer/Multilink, with luting material remaining on the post surface and exposure of root canal wall dentin.  A - Tooth half: The dentin surface of the root canal wall is exposed to 90 %, with some luting material remaining (10%) in the coronal part (right).  B - Post: The post surface is covered with luting material (90%), showing smaller and larger voids on the surface. A small area (5%) of the post surface is exposed in the coronal area (right), showing the longitudinally oriented fibers.  C - Tooth half: Magnification of the boxed area in picture A, showing the exposed dentin surface (lower and middle) with dentinal tubule orifices, intertubular dentin and thin luting material remnants (right lower corner). The upper area of the image is representing the fractued dentin surface, after splitting the tooth longitudinally in two halfes, showing dentinal tubules and irregularily fractured intertubular dentin.  C 102   Figure 57. SEM images of mixed failure between dentin and luting system and luting system and post. The sample is characteristic for LuxaBond/LuxaCore Z with luting material remaining on the post surface and exposure of root canal wall dentin as well as material remaining on the root canal wall and exposure of the post surface.  A - Tooth half: The dentin surface of the root canal wall is exposed to 70 %, with luting material remaining (30%) in the coronal part (right), showing identations of the macro-rententions. B - Post: The post surface is covered with luting material (70%), showing debris remnants, embedded in the luting material in the middle of the posts. The post surface is exposed in the coronal area (right), showing spiral-shaped macro-retentions and longitudinally oriented fibers.  C - Tooth half: Magnification of the boxed area in picture B, showing the exposed post surface (right) with macro-retentions and longitudinally oriented fibers. The remaing post is coverd with luting marerial. Dentin debris is embedded in the lutig material (arrow), showing cracks (drying artifacts).  103  5.1.2.3 Combination of Influencing Factors Post Fit and Luting System  Figure 58. Pull-out forces (N), subdivided by luting system and post fit, in relation with the control. ANOVA revealed significant influence of the post fit on the pull-out force for RXU, MLP_ML and LB_LCZ. Post-hoc testing (Dunnett T3) showed significant differences for (a) to (f) at α’ = 0.004. Co = control; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z; C = Congruency; MIC = Medium incongruency; HIC = High incongruency; *= Statistically significant difference  The descriptive data for the pull-out force and the failure mode analysis were presented in Table 28 (p. 219) - Table 30 (p. 220).  The influence of the post fit on the pull-out force was tested separately for the four luting systems using ANOVA. Since the Levene test revealed no equality of variances, the local significance level was adjusted to α’ = 0.001 for secure 104  interpretation of the ANOVA results. The post fit had a significant influence (ANOVA, p < 0.001) for all three adhesive luting systems (RelyX Unicem, Multilink Primer/Multilink and LuxaBond/LuxaCore Z). No significant influence of the post fit on pull-out force was found for the resin-modified glass ionomer cement Fuji Plus (ANOVA, p = 0.465) (Figure 58, p. 103).  Pairwise comparisons were carried out for the groups, when ANOVA revealed general differences (RelyX Unicem, Multilink Primer/Multilink and LuxaBond), using the Dunnett T3 test. To offset α-error accumulation, when applying multiple pairwise comparisons, the local significance level was adjusted with the Bonferroni correction procedure (α’ = α/12 = 0.004). For all three adhesive luting systems, a significant reduction in pull-out force (Dunnett T3, p < 0.004) was found when comparing congruent post fit with medium incongruent and with high incongruent post fit. No significant differences were found for all three adhesive luting systems, when comparing medium congruent post fit with high incongruent post fit (Dunnett T3, p > 0.004) (Table 34, p. 221 - Table 37, p. 222).  The LuxaBond/LuxaCore Z group achieved the highest pull-out forces for all post fits, when comparing the data with the other luting systems. All luting systems, independent on the post fit, achieved significantly higher pull-out forces than the control group (p < 0.004). The co-factor of variation (Table 28, p. 219 - Table 30, p. 220) was lowest for the Fuji Plus (7.4 – 12.2) groups, followed by LuxaBond/LuxaCore Z (9 – 15.5) and Rely X Unicem (13.3 – 21.1), while the highest values were found for the Multilink Primer/Multilink group (23.3 – 24.2).  105   Figure 59. Failure mode (%), subdivided by luting system and post fit. FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilik Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z; C = Congruency; MIC = Medium incongruency; HIC = High incongruency; F_D = Failure within dentin; F_D_LS = Failure between dentin and luting system; F_LS = Failure within luting system; F_LS_P = Failure between luting system and post; F_P = Failure within post   The failure mode analysis for Fuji Plus showed the main failure between the luting system and the post. With decreasing post fit, there was a continuous increase in the failure between the luting system and the dentin (Table 31, p. 220 - Table 33, p. 221, Figure 59, p. 105). 106  For RelyX Unicem the predominant failure mode was found between the luting system and the dentin, with only slight variation within the three post fit groups (Table 31, p. 220 - Table 33, p. 221, Figure 59, p. 105). The main failure for Multilink Primer/Multilink was found between the luting system and dentin. For the congruent post fit, there was also 10% failure between the luting system and the post detected. With decreasing post fit, a decrease in failure between the luting system and post was detectable (Table 31, p. 220 - Table 33, p. 221, Figure 59, p. 105). The failure analysis for LuxaBond/LuxaCore Z showed the main failure between the luting system and the dentin but also considerable failure between the post and the luting system. For the congruent post fit group there was also a small percentage of failure within the post and within the luting system detected (Table 31, p. 220 - Table 33, p. 221, Figure 59, p. 105). 107  Chapter 6: Discussion 6.1 Methodological Factors 6.1.1 Dentin Substrate Selection and Storage Based on previous studies (52, 56, 314, 382, 386, 435-437, 449, 456), estimations revealed a sample size of 20 samples per group, resulting in the requirement of at least 260 single rooted teeth. The teeth should ideally have similar dentin properties, fulfill the predetermined inclusion criteria (see Materials and Methods, p. 61) and have a root diameter equal or larger than 4.5 mm in the cervical area. Considering all these requirements, the collection of human teeth in the desired quality and quantity was challenging. Therefore, the substitution of human teeth with bovine, deciduous teeth was considered. There has not been full agreement on the suitability to use bovine teeth as an alternative substrate because of detectable structural differences (i.e. tubule size, tubule density, tubules/mm2) of the two dentin substrates (496, 498). However, most available comparative studies assessed coronal bovine and human dentin (494-498). Only two in vitro studies, focusing on the comparison of bonding to root canal dentin in human and bovine teeth, were identified (456, 501).  The first study (501) evaluated the push-out bond strength (MPa) in bovine (tooth type and dentition not reported) and human (teeth extracted for orthodontic reasons) root sample slices of 1.5 mm thickness (n = 10 teeth per group per group, n = 60 slices per group). The FRC-posts were substituted with an individually manufactured composite post, by pouring the composite (Duolink Composite Luting Cement) in a silicone mold. Surface preparations (i.e. degreasing to remove the 108  silicone oil) were not reported. The individual posts were luted, using a dual-cured, self-conditioning adhesive (AllBond® 2 Universal) and a dual-cured resin cement (Duolink Composite Luting Cement). The bond strengths were significantly higher (p = 0.026) in human teeth (9 MPa), compared to bovine teeth (4 MPa). The failure mode was not assessed. Another study, conducted by our research team (456), compared the pull-out bond strength (MPa) of posts, luted with five different luting system types (i. conventional glass ionomer cement (Ketac Cem), ii. resin-reinforced glass ionomer cement (Fuji Plus), iii. self-conditioning resin cement (RelyX Unicem), iv. self-conditioning adhesive and resin cement (Multilink Primer/Multilink) and v. Etch & Rinse adhesive and resin cement (LuxaBond/LuxaCoreZ)), in human (n = 250 teeth, 50 teeth per group) and bovine teeth (n = 250 teeth, 50 teeth per group). The influence of the substrate on the bond strength was significant. When comparing the bond strength, generated in bovine and human teeth, within one luting system type, no significant differences were found for resin-reinforced glass ionomer cement (bovine = 8.6 MPa, human = 7.9 MPa) and self-conditioning resin cement (bovine = 10.4 MPa, human = 11.0 MPa). Slight, however significant differences were detected for the conventional glass ionomer cement (bovine = 5.4 MPa, human = 6.3 MPa). Using the self-conditioning adhesive and resin cement (bovine = 12.7 MPa, human = 9.4 MPa) and the Etch & Rinse adhesive and resin cement (bovine = 15.7 MPa, human = 10.4 MPa), significant differences were found. Failure mode analysis showed considerable differences between bovine and human teeth only for the failure 109  distribution of the self-conditioning resin cement, with higher failure between luting system and dentin in bovine teeth, compared to human teeth (456).  These two previously described studies revealed contradictory information, when analyzing the results of the self-conditioning adhesive with resin cement. In the AllBond Universal/Duolink group (501), the bond strength were higher in human than bovine teeth, while in the Multilink Primer/Multilink group (456) the bond strength were significantly higher in bovine teeth, compared to human teeth.  Based on these results, there was no clear evidence whether the substitution of human teeth with bovine teeth is feasible. However, we decided to use bovine teeth for this study because of the previously described advantages, in terms of sample standardization and high quantity acquisition of samples with adequate quality. In addition, the luting materials, used in the present study, were similar to the materials, used in the above-mentioned study by our group (456). Therefore, it will be possible to use the previously acquired data in bovine and human teeth for comparison and interpretation of the results of the present study.  6.1.2 Reinforcement and Luting Materials 6.1.2.1 Posts The Macro-LockTM Post IllusionTM X-RO® system as well as the D.T. Light-Post® Illusion™ X-RO® system are both produced by RTD in France. Both post systems are milled form the same fiber-reinforced composite work pieces, consisting of patented silanized quartz fibers, coupled to an epoxy resin matrix. The Macro-Lock Posts system was selected for this study because the physical (i.e. light transmission 110  (414, 544), fiber content (367, 545) and mechanical properties (i.e. interlaminate shear (546), cyclic fatigue (367), flexural strength (367, 547-549)) of the RDT post systems have been proven to be consistently superior in multiple studies (367, 414, 544-549). The macro-retentive design has been shown to improve the bonding properties of conventionally and adhesively luted FRC-posts (56, 436). In addition, our research group has conducted previous studies, using the Macro-Lock Post system (56, 436, 467), which allows for comparison and improved interpretation of the present study results.  6.1.2.2 Luting Systems The luting systems, selected for this study, represent a variety of luting system types to evaluate the influence of the post fit when applying: i. different adhesive mechanisms (i.e. bonding via calcium ions, chemo-mechanical bonding), ii. conditioning methods (i.e. Etch & Rinse adhesive, self-conditioning adhesive, self-conditioning cement) and iii. luting material compositions (i.e. glass ionomer cement, resin cement). All selected materials (i. conventional glass ionomer cement (Ketac Cem) (52, 56, 382, 436, 437, 456, 467, 550-554), ii. resin-reinforced glass-ionomer cement (Fuji Plus) (52, 56, 382, 436, 437, 456, 467, 555), iii. self-conditioning resin cement (RelyX Unicem) (52, 56, 314, 381, 382, 436, 437, 456, 467, 523, 556, 557), iv. self-conditioning adhesive (Multilink Primer/Multilink) (52, 56, 314, 382, 386, 435-437, 441, 451, 456, 457, 558, 559) and v. Etch & Rinse adhesive and resin cement (LuxaBond/LuxaCore Z) (52, 56, 314, 382, 386, 436, 437, 449, 456, 467, 560)) were frequently used in previous studies, by other researches (441, 451, 457, 523, 550-111  558, 560) as well as our own research team (52, 56, 314, 381, 382, 386, 436, 437, 449, 456, 467), for cementing metal and FRC-posts in human and bovine teeth, and demonstrated consistently good bonding properties. One study, comparing two luting systems of each of the above-mentioned luting system type categories, identified these specific luting systems to have superior bonding properties, compared to the second tested material within the luting system category (52).  Ketac Cem, a clinically widely used conventional glass ionomer luting cement, was used in combination with a prefabricated titanium post as control. Conventionally cemented, custom-cast or prefabricated metal posts were successfully used for decades under clinical conditions to restore endodontically treated teeth with compromised coronal tooth structure. Therefore, it was indicated to compare the more recently introduced technique, using conventionally or adhesively luted fiber posts, with the established technique, using conventionally cemented metal posts (52, 56, 62, 382, 436, 437, 456, 467). The availability of comparative data for all selected luting systems will allow for improved interpretation of results, extracted from the present study.  6.1.3 Evaluation of Bonding Properties Laboratory test have the advantage that certain influencing factors can be tested under standardized conditions by reducing other interfering factors, which are present under clinical conditions. In vitro and ex vivo tests are valuable during preclinical evaluation of new treatment methods, before these are introduced to regular patient care. However, care should be taken when interpreting laboratory 112  results and how to transfer the knowledge to the clinical situation (514-516). Different methods can be applied to evaluate the bonding properties of root canal posts in vitro or ex vivo (i.e. assessment of dislodgement forces, micro-leakage evaluation, fracture resistance assessment, failure mode analysis) (52, 514, 518, 525, 561-564). Using different laboratory methods to test the same materials and influencing factors - in a step-wise approach - can possibly increase the predictability value for the clinical performance.   6.1.3.1 Sample Preparation and Testing Procedure The aim of this study was to evaluate the bonding properties of differently luted macro-retentive FRC-posts with congruent or incongruent post fit, by assessing the dislodgement force. Dislodgment forces can be acquired by applying pull-out or push-out test designs. For the present study, the pull-out test design was selected to enable the evaluation of the influence of the macro-retentive post design over the entire length of the post cavity on the bonding properties. This would not be possible when using the thin-slice push-out test design. Another advantage, when using the pull-out test design, is the less time-consuming sample preparation procedure, compared to the push-out test design (52, 514, 518). Under clinical conditions, failure of post-retained restorations is often associated with de-bonding (61, 377-380, 473-476, 481, 482). Therefore, when testing bonding properties in vitro, the failure should also lay mainly within the bonding interfaces (i.e. failure between dentin and luting system, failure between post and luting system). When using the push-out testing procedure, failure often occurs within the post, especially in posts with inferior 113  mechanical properties (381, 523, 524). This phenomenon adulterates the evaluation of the bonding properties. Considering all these facts, for this study, the pull-out test design was selected because it accommodates the purpose of the evaluation best. However, when interpreting the results, the disadvantages of the pull-out testing have to be bared in mind (i. non-uniform stress distribution, ii. possible jamming of luting system fragments in the gap between the post and the cavity wall, leading to increased friction during the pull-out procedure, iii. influence of crack propagation).  An important point, when preparing pull-out samples, is to ensure exact alignment of the post with the root canal axis, during the luting, embedding and the pull-out procedure to reduce the occurrence of erroneously high pull-out forces, when dislodging the post non-axially, in an angle. Axial alignment of the post with the cavity is especially challenging, when luting an incongruent post, namely when a smaller post is introduced into a wider cavity without primary passive fit. Therefore, for this study, a novel method was developed to ensure a centered and axially aligned post insertion of incongruently fitting FRC-posts (post sizes 1 and 3) in an oversized post cavity (size 6), including the sample slice preparation (Figure 29,p. 72 - Figure 36, p. 77), the post cavity preparation (Figure 40, p. 81, Figure 41, p. 82), the post insertion (Figure 42, p. 83, Figure 43, p. 85), the embedding procedure (Figure 47, p. 88, Figure 48, p. 88) and the pull-out testing (Figure 49, p. 90). For the pull-out testing, aside from the axial alignment in the drill chuck, a 2D ball bearing was added to the upper part of the jig to allow free sample movement and to avoid tilting of the sample in a non-axial position, during the testing procedure.  114  The pull-out forces for each group revealed a low co-factor of variation (minimum 7.4, maximum 24.2), which is well below the proposed threshold of 30-40% for samples, involving biological material, such as dentin (536). This indicates successful standardization of the study parameters by: i. using bovine teeth of the same tooth type from animals with a similar age range, ii. post insertion by the same experienced operator and iii. exact post alignment during the entire sample preparation and pull-out testing procedure.  6.1.3.2 Failure Mode Analysis Aside from the dislodgement forces, the failure mode analysis provides valuable information about the bonding properties of different luting system and post combinations, when bonded to root canal dentin. The weakest link in the system can be identified with the aim to improve the bonding in this area (52, 56, 514, 565, 566).  Different systems for failure mode analysis have been introduced, including the report of adhesive and cohesive or mixed failure of the components (431, 523, 533-536) or the detailed report of failure within the components (i.e. dentin, luting system, post) or within the interfaces between the components (between dentin and luting system, between post and luting system) (52, 56, 381). The latter method seems to be advantageous for identifying the weakest link in order to improve the bonding properties of the entire compound. Lack of a possibility to conduct a complete failure mode analysis of the post and the tooth substrate in pull-out samples is discussed as a disadvantage in the literature (52, 56, 381, 567-570). However, this problem was overcome - in previous 115  studies of our group (52, 56) as well as in the present study - by splitting the tooth in two halves to ensure failure mode analysis of the entire post cavity surface as well as the post.   6.1.4 Study Limitations This in vitro study on extracted teeth is part of an experimental series and should be seen in the context of previously completed (52, 56, 314, 381, 382, 386, 435-437, 449, 456, 467) and prospectively planned studies from our group. The study was conducted to evaluate initial bonding properties of conventionally and adhesively luted fiber-reinforced composite posts with varying post fit conditions. The aim was to identify luting materials with superior bonding performance in combination with incongruently fitting posts for further evaluation and to eliminate materials with less favorable properties. The advantage of laboratory studies is that specific influencing factors - in this study post fit and luting system selection - can be evaluated without the interference of multiple, uncontrollable factors, occurring under clinical conditions (i.e. patient-, tooth- and/or restoration-related factors (62, 346, 357, 377, 473, 474, 478, 481, 482). Comparisons between results from in vitro and in vivo studies in general are scarce (515, 536, 571-574) and no comparative evaluation could be found for post-retained restorations. The existing comparative evaluations for coronal restorations (572, 573) show in general low to medium correlation between laboratory and clinical findings. Correlations exist between bond strength of aged laboratory samples and marginal discoloration of Class V in vivo restorations (572, 573) as well as in vitro shear bond strength data and the annual failure rate of in vivo restorations 116  (573). A comparative evaluation of bond strength results, achieved with different test methods, revealed a high scatter of bond strength data (536), however pooling of laboratory results improves the correlation with clinical findings (574). The luting materials, tested in this present study, were used in previous studies to evaluate different influencing factors ((52, 56, 382, 386, 436, 437, 449, 456, 467) with consistent tendencies in the results. However, aside from the known disadvantages of laboratory evaluations, in vitro studies are still a valuable tool during the preclinical testing phase for novel materials or procedures to reduce the risk of catastrophic failure, when applied under clinical conditions (575-578). For this study, bovine teeth were used as an alternative substrate for human teeth. Comparative studies between human and bovine teeth on bonding properties of root canal posts are scarce (456, 501). The dentin substrate can influence the bond strength of some luting materials (456, 501), while there is no difference in bond strength for other luting material categories (456). The interpretation of results, achieved from testing on bovine teeth, should be conservative and take available findings on human teeth (314, 386, 456) into consideration for comparison. Depending on the post space preparation technique, the root canal dentin surface can be pretreated with irrigation solutions (422, 579-581) or contaminated with intra-canal medicaments (581-584) or root canal sealer (424, 426, 585, 586), which can alter the bonding properties of luting materials. In the present study, the post space was irrigated with distilled water and the dentin surface was not contaminated with endodontic medicaments or sealers to assess purely the bonding properties, without additional influencing factors. A future study will simulate the 117  clinical situation more closely by using human immature premolars, disinfecting the root canal with irrigation solutions and short- or long-term calcium hydroxide intra-canal dressing as well as contaminating the root canal walls during the root canal filling procedure with endodontic sealers and gutta percha. In addition, aging procedures (thermal cycling and chewing simulation) will be applied. The present study evaluated initial pull-out forces after 24 hours setting time. Comparative assessments of laboratory results and clinical performance show better correlation between in vitro bond strength testing and clinical results when aging procedures are applied, before bond strength testing (572, 573). These aging procedures (i.e. fluid storage, thermal cycling, chewing simulation or combinations of the three methods) can partly simulate the time-dependent deterioration of the bonding between dentin and luting or restorative materials, as found under clinical conditions (517, 526, 587, 588). A wide range of fluid storage duration (57, 341, 554, 579, 589), numbers of cycles during thermal (435, 440, 455, 463, 485, 579) and mechanical (460, 463, 493, 590, 591) aging procedures or a combination of the methods (463, 467, 592-594) is found in the literature. The application of valuable aging procedures, simulating clinical usage of 2-5 years, is time-consuming and cost-intense. In a previous study of our group, we have evaluated the bonding performance, of the luting materials and the post from the previous study, after aging by thermal cycling and chewing simulation (467). These previous results can aid to estimate the long-term bonding performance when interpreting the initial bond strength from the recent study. Therefore, to evaluate the influence of the post fit on the bonding performance, initial pull-out force assessment was applied to reduce the 118  duration and costs of the study. The above-mentioned prospective study will include the application of long-term fluid storage in combination with thermo-mechanical cycling to simulate a clinical usage period of 5 years.  6.2 Results 6.2.1 Dislodgement Forces and Failure Mode In the present study, the results of the pull-out force assessment were reported in Newton, since accurate bonding area evaluation and calculation was not achievable, especially for the incongruent post fit groups. However, comparison between the different groups within this study was feasible because the post cavity size and the height of the sample slices were standardized, with very minimal tolerance. The direct comparison with other studies, reporting bond strength in Mega Pascal is difficult however, tendencies can be discussed. Other aspects that need to be considered, when comparing the present results with other studies, using the same luting materials, are: i. selection of tooth substrate, ii. post material, shape, and surface design, iii. post surface pretreatment, iv. application of aging procedures and v. selection of test method for evaluating the bonding properties.  6.2.1.1 Post Fit as an Influencing Factor  The results of the present study revealed that the post fit, independent of the luting system selection, had a significant influence on the pull-out forces (Table 22, p. 217, Table 24, p. 217, Figure 51, p. 96). When comparing the pull-out forces of the different post fit groups, significant differences were detected between the congruent 119  post fit and the two different incongruently fitting posts. Comparing the results of the medium incongruency and high incongruency group, no significantly differences were found. Therefore, thicker cement layers seem to negatively influence the bonding properties of conventionally and adhesively luted FRC-posts. Interestingly, the failure mode distribution did not significantly change within the different post-fit groups (ca. 65% failure between dentin and luting system, ca. 35 % failure between post and luting system) (Table 23, p. 217, Figure 52, p. 97). All FRC-post, irrespective of the post fit achieved significantly higher pull-out forces, compared to the conventionally luted titanium post, which served as a control group. Studies, focusing on the influence of the post fit or cement layer thickness on dislodgement forces for luted posts to root canal dentin, are scarce (438-440, 442, 443, 493, 595). The results of the present study are entirely or partly in accordance with five other studies (438-440, 443, 493). However, these studies employ various designs, which differ from the design, applied in the present study. In the study by Egilmez et al. (440) parallel, individually made zirconia posts and FRC-post (everStick post) of two different sizes (1.2 mm and 1.5 mm) were luted to a standardized post cavity (1.5 mm) with parallel walls, in teeth of unknown origin, using a self-conditioning resin-cement (Clearfil SA Cement). The dislodgement forces were tested with the push-out design (2 mm thick slices) and bond strengths were calculated in MPa. Significant differences were found between the congruently and non-congruently fitting zirconia posts, while no differences were found between the two post fits for the individually manufactured FRC-post. The discrepancy in the results, between the two post systems, can be explained with the high failure rate 120  within the FRC-post, which was also found in other studies (381, 523, 524). The failure within the post, even at low load applications during the push-out procedure, indicates inferior mechanical properties of the post and leads to impaired test results. Under these circumstances, the results are erroneously lower than the possibly achievable values because the post fails before failure occurs within the bonding interfaces (dentin/luting system, post/luting system). Therefore, only the results for the zirconia post should be taken into consideration, when interpreting this study. The second study, by Schmage et al. (443) assessed the influence of the post fit by preparing 12 mm deep post cavities in two sizes (ISO 90 and 110) and inserting posts of one standardized size (ISO 90) with 5 different adhesive resin luting cements or built-up materials into human extracted teeth. There is no indication that special measures were taken to insert the incongruently fitting post centered and aligned with the post cavity. The teeth were subjected to artificial aging by thermal cycling, before the dislodgement forces were evaluated, using a pull-out testing approach. The results were reported in Newton. Statistical analysis revealed a significant influence of the post fit as well as the luting system. These findings are in accordance with the results of the present study. However, the pull-out forces, reported in the study by Schmage et al. (443), with posts inserted into a 12 mm deep post cavity are considerably lower (average pull-out force range for: fitting posts 267-454 N, non-fitting posts 152-301 N), compared to the results of the present study where posts were inserted into 6 mm deep cavities (average pull-out force range for: congruent post fit 327-610 N, medium incongruency 352-538 N, high incongruency 327-484 N). These discrepancies could be partly explained with the influence of the artificial aging 121  in the study by Schmage et al. (443, 514) and the differences in dentin substrate (443, 456). The third study, by da Rosa et al. (439) assessed the influence of the cement layer thickness on the bond strength of FRC posts, luted to root canals in bovine teeth. In addition, half of the teeth were subjected to mechanical cycling for aging, before performing the push-out testing. The cement layer thickness had a significant influence on the bond strength both, in the aging and the non-aging samples, with significantly higher bond strength in the groups with the thinner cement layer.   The fourth study, by D’Arcangelo et al. (438), evaluated the influence of the post fit by varying the post cavity size (ISO 90, 100, 120 and 140) and by keeping the post size (FRC-post, 0.9 mm) standardized. The posts were luted to the post cavities in human teeth, using a usually well-performing, chemically curing adhesive and resin composite (Panavia 21). Before testing the bonding properties, the samples underwent thermal cycling. The samples were submitted to pull-out testing and the force was reported in Newton. The highest pull-out forces were reported for the incongruent post fits (cavity size ISO 100 (182 N) and 120 (211 N)), followed by the congruent post fit (ISO 90 (139 N)) and the maximally incongruent post fit (ISO 140 (91 N)). The failure was reported to occur solely between dentin and luting system. The measured pull-out forces appear to be low, compared to findings from another study (314) where Panavia 21 achieved on average higher initial bond strength (13 MPa) than Multilink Primer/Multilink (11 MPA) and slightly lower bond strength than LuxaBond/LuxaCore Z (16 MPa) in a push-out test design. When comparing the pull-out forces of the study by D’Arcangelo et al. (438) (post length 8 mm, average pull-122  out force range 91-211 N) with the results of our present study (post length 6 mm, average pull-out force range 327-610 N) and previous studies (post length 6-10 mm, average pull-out forces 132-935 N) (52, 56, 382, 386, 436, 437, 449, 456, 467), the pull-out forces appear to be relatively low. This could be explained by the application of thermal cycling as an aging procedure, before pull-out testing in the study by D’Arcangelo et al. (438). The fifth study, by Souza et al. (314, 493), assessed the influence of the cement layer thickness by preparing size 3 post cavities for the insertion of size 1 and 3 posts. The teeth were built up with cores and subjected to chewing simulation, before evaluating the bond strength, using push-out testing. The cement layer thickness significantly influenced the bond strength, with the congruently fitting post (size 3) achieving higher values, compared to the incongruently fitting post (size 1).  Two other studies, focusing on the influence of the cement layer thickness on bonding properties of posts, reveal contradictory results, compared to the present study.  The first study by Perez et al. (442), presenting contradictory results to our present outcomes, assessed the influence of the cement layer thickness by luting different FRC-post sizes (size 1 and 3) to a standardized post cavity (size 3), using an adhesive in combination with resin luting cement. However, no indication was given if and how the central and axial alignment of the incongruently fitting post was achieved. The dislodgement force was tested in a push-out test design with 1.5 mm thick test samples. The comparison of the bond strengths of the low thickness and high thickness cement layer did not reveal statistically significant differences. One 123  explanation for this result could be the non-axial luting of the incongruently fitting post, leading to increased push-out forces of the possibly tilted post.  The second study, by Assif & Bleicher (595) evaluated the post fit by varying the post size as well as the post cavity size. Cylindrical, serrated metal posts were luted with a non-adhesively bonded resin composite to parallel-walled post cavities with a cement layer gap of either 0.25 mm or 0.5 mm. There was no indication that specific measures were applied to ensure centered and axial alignment of the post in the larger-diameter post cavities. No statistically significant differences were found when comparing the 0.25 mm and 0.5 mm cement layer thickness results, irrespective of the post size. The results of this study should be interpret with caution, since the composite material, used for luting the serrated metal posts, was possibly inconsistently mixed and diluted, before inserting it into the root canal. In addition, the composite resin was used without conditioning the dentin or applying an adhesive system. Therefore, no chemo-mechanical bond between the post cavity dentin and the luting composite resin can be expected. The reported sole failure between the luting composite and the dentin supports this hypothesis. All the above-mentioned pitfalls of this study lead to reported tensile forces with a high standard deviation. The validity of the results is therefore questionable.  6.2.1.2 Luting System as an Influencing Factor  The results of the present study on bovine teeth showed that the luting system selection significantly influenced the bonding properties, irrespective of the post fit (Table 25, p. 218, Table 27, p. 218, Figure 53, p. 98). When comparing the pull-out 124  forces of the different luting systems, significant differences were found between all luting systems, except for the self-conditioning resin cement RelyX Unicem and the combination of the self-conditioning adhesive and resin cement Multilink Primer/Multilink. The by far highest pull-out forces were achieved with the Etch & Rinse adhesive and resin cement LuxaBond/LuxaCore Z (544 N), followed by the resin-reinforced glass ionomer cement Fuji Plus (441 N) and then the similar performing self-conditioning resin cement RelyX Unicem (391 N) and self-conditioning adhesive and resin cement Multilink Primer/Multilink (379 N). All luting systems, used for inserting the FRC-posts, achieved significantly higher pull-out forces than the conventional glass ionomer cement Ketac Cem, which was used to insert the congruently fitting titanium post of the control group.  The superior bonding performance of LuxaBond/LuxaCore Z could be partly explained with the dentin conditioning, including a separate etch and rinse procedure (smear layer removal, exposure of the superficial collagen fibers, opening and enlarging the dentinal tubule orifices) and the two-step adhesive application, ensuring an adequate coupling of the hydrophobic resin luting cement to the hydrophilic dentin substrate (596). LuxaBond is an acetone-based dual-cured adhesive system, consisting of a curing enhancer and a one-step, two-bottle adhesive, which is applied after the etching procedure to moist dentin. Equally, adequate bonding to the dentin substrate as well as to the post surface is a precondition, when using resin composite luting materials, which shrink during the polymerization reaction. The coupling via the adhesive system should be strong enough to counteract the shrinkage stress during the polymerization reaction to ensure durable bonding without gap formation. 125  LuxaCore Z is a dual-cured nano-filler resin built-up and luting material with added zirconia particles, which has superior mechanical properties, such as compressive strength (380 MPa (597)), compared to materials solely indicated as resin luting cements (RelyX Unicem 145-244 MPa (598, 599), Multilink 240-280 MPa (600)) or conventional (Ketac Cem 79-87 MPA (598, 599)) and resin-reinforced glass ionomer luting cements (Fuji Plus 120-142 MPa (598, 599)). The failure mode analysis of LuxaBond/LuxaCore Z showed predominant failure between dentin and luting system (ca. 65%), followed by failure between the post and the luting system (ca. 35%) at significantly higher pull-out forces, compared to the self-conditioning resin cement RelyX Unicem and the self-conditioning adhesive and resin cement Multilink Primer/Multilink, which showed almost exclusively failure between dentin and luting system, at significantly lower pull-out forces. These findings indicate that the bonding ability of the multi-step Etch & Rinse adhesive LuxaBond, in combination with the nano-filled resin composite LuxaCore Z, to dentin and the post surface is balanced and superior, compared to the other two resin cement luting systems. In addition, LuxaBond/LuxaCore Z showed the lowest co-factor of variation (CV 18) within the three resin luting systems (Rely X Unicem (CV 21), Multilink Primer/Multilink (CV 28)), which can be discussed as an indicator for low technique-sensitivity. The argument, that Etch-& Rinse adhesives and resin luting materials are technique-sensitive and challenging to apply in root canals and therefore, self-conditioning materials should be used for cementing FRC-posts, cannot be supported by the findings of this study, which is in accordance with previous recommendations (416, 420). 126  The pull-out forces for the self-conditioning resin cement RelyX Unicem and the self-conditioning adhesive and resin composite Multilink Primer/Multilink were similar and significantly lower than for LuxaBond/LuxaCore Z and Fuji Plus. RelyX Unicem does not require dentin conditioning, before insertion of the resin luting cement. It contains phosphoric acidic methacrylate monomers, which react with the calcium ions of the hydroxyl apatite of the dentinal surface, with the aid of remaining water from the dentin. The amount of moisture and possible contamination of the dentin (i.e. with hydrogen peroxide) can influence the bonding performance (601). In the present study, the failure was found between dentin and luting system, at relatively low pull-out forces, indicating that the bonding between post and luting system is stronger than between luting system and dentin. Similar failure mode results were found for the self-conditioning adhesive Multilink Primer in combination with Multilink. Multilink Primer contains acids within the one-step adhesive system for dissolving or modifying the smear layer and the superficial inorganic dentin components. The dissolved components remain within the hybrid layer, after curing. In addition to the acidic component, Multilink Primer also contains amphiphilic monomers for covering the hydrophilic collagen fibers as well as a hydrophobic resin component for infiltrating the collagen network and establishing the link between the adhesive and the resin luting cement. Even though, these two luting systems were selected for the study because of their superior performance, compared to other materials from the same category (52), they could not achieve dentin bonding, comparable to the more complex multi-step adhesive and resin cement combination LuxaBond/LuxaCore Z. 127  Fuji Plus, a resin-reinforced glass ionomer cement, achieved higher pull-out forces than Rely X Unicem and Multilink Primer/Multilink however, lower pull-out forces than LuxaBond/ LuxaCore Z. Before insertion of the luting material, the dentin was pre-treated with Fuji Plus Conditioner, consisting of a mild acid (10% citric acid), to dissolve the smear layer and remove the components during the rinsing procedure. The in this manner prepared dentin surface provides good conditions for chemical bonding of the glass ionomer cement to the calcium ions of the exposed dentin surface, without the interposition of a mechanically weak smear layer. The failure mode analysis showed the main failure between the post and the luting system (ca. 90%) and only a small percentage of failure between the dentin and the luting system (ca. 10%). These results indicate that the bonding between the dentin and the luting system is stronger than the bonding between the post and the luting system, at reasonably high pull-out forces. The reason for the failure between the post and the resin-reinforced glass ionomer cement could lay in insufficient wetting of the hydrophobic post surface with the hydrophilic cement (52, 56). Aside from the bonding performance, the technique sensitivity of the material seems to be comparably low (co-factor of variation 10). However, one disadvantage of resin-reinforced glass ionomer cements is the water absorption and the associated subsequent expansion of the material (52, 56, 400, 602). Therefore, the indication to use this type of material for the insertion of posts to root canals, especially with larger cement layer thicknesses, should be critically discussed. Swelling of the cement in the post cavity could lead to the development of vertical root fractures. However, in adequately sealed and restored teeth, the post-cement-dentin compound should not 128  be in contact with moisture or fluids and therefore, water uptake and expansion by the cement should be ruled out. Wide varieties of studies on FRC-posts, evaluating the influence of the luting system selection on the bonding performance, are available in the literature. For discussing the results of the present study in the context of the literature, studies, involving at least one of the luting systems, used in the present study, were selected (52, 314, 381, 382, 386, 389, 435-437, 441, 449, 451, 456, 457, 467, 558, 560, 603-605). As in the present study, the majority of studies showed a significant influence of the luting system selection on the bonding performance. These studies were conducted on human teeth (push-out test (314, 381, 436, 457, 558, 560), pull-out test (382, 437, 456), micro-tensile test (605)), bovine teeth (pull-out test (52, 56, 436, 441, 456, 467)) and on post-luting system samples (push-out test (451, 603), pull-out test (386)).  One of these studies evaluated the influence of the luting system selection as well as the influence of the dentin substrate (bovine and human), using the same luting systems as the present study (456). The influence of the luting system selection was significant for both dentin substrates. However, the ranking of the materials, based on the generated pull-out forces, was different for human (1=RelyX Unicem (11.0 MPa), 2=LuxaBond/LuxaCore Z (10.4 MPa), 3=Multilink Primer/Multilink (9.4 MPa), 4=Fuji Plus (7.9 MPa), 5=Ketac Cem (6.3)) and bovine teeth (1= LuxaBond/LuxaCore Z (15.7 MPa), 2= Multilink Primer/Multilink (12.7 MPa), 3= RelyX Unicem (10.4 MPa), 4=Fuji Plus (8.6 MPa), 5=Ketac Cem (5.4 MPa). These results should be taken into consideration, when interpreting the results of the present study. 129  In human teeth, the bonding performance of the simplified self-conditioning resin cement RelyX Unicem was similar to the multi-step Etch & Rinse adhesive LuxaBond in combination with the resin composite material LuxaCore Z, while the bonding performance of LuxaBond/LuxaCore Z was significantly superior over RelyX Unicem in bovine teeth. These differences could be explained by the different dentin structures of the two substrates. The tubule size and tubule density as well as the area of inter-tubular dentin is higher in bovine than in human teeth (496, 499). This may led to the generation of a lager hybrid layer area as well as more and thicker resin tags in bovine teeth compared to human teeth, when using the Etch & Rinse adhesive LuxaBond, resulting in higher pull-out forces. The bonding properties of the self-conditioning resin cement were not influenced by the dentin substrate (bovine 10.4 MPa, human 11.0 MPa), since the adhesion relies mainly on the bonding to the calcium ions and the generation of a superficial hybrid layer and not on the formation of resin tags (496, 499, 556, 606, 607). Contradictory results to the present study, with the luting system selection not influencing the bonding performance, were only found in three studies (389, 449, 604).  The first study evaluated the influence of post pretreatment, when inserting posts with different adhesive resin luting systems in bovine teeth (449). In this study, the pretreatment method influenced bonding properties, while the luting system selection did not. One explanation could be that the used post system had a smooth surface. The main failure for all luting systems occurred between the post and the luting system (449), while in the present study, using a macro-retentive FRC-post, the 130  main failure for the adhesive luting systems was found between the luting system and the dentin. The second study evaluated the influence of the post type, luting system and localization within the root canal on push-out bond strength in human teeth (604). The two resin luting cements (AllCem and Multilink) were combined with an Etch & Rinse adhesive from another manufacturer (Excite DSC) and two different post systems each, resulting in 4 groups. As per the manufacturer’s recommendation, Multilink should be used in combination with the self-conditioning adhesive Multilink Primer, while there is no specific recommendation for AllCem. The push-out bond strength, reported in the study ranged from 8.7 to 10.9 MPa, within the four groups. However, no statistically significant influence of the luting system selection or the post type was found, while the localization within the root canal was significantly influencing the push-out bond strength. This result could be due to an insufficiently small sample size (n = 8) per group, while testing for three influencing factors. In addition, the use of non-recommended bonding agent types with the resin luting systems could also contribute to the contradictory outcome. The third study evaluated the influence of various post surface pretreatment methods on the bonding properties of three resin luting cements to the post surface, using a micro-tensile test (389). The post pretreatment was significantly influencing the bond strength (p < 0.001) while the luting system selection was not (p < 0.07), at a significance level of 0.05. In this study, only the adhesion of the interface between post surface and luting system was evaluated. All three luting materials were dual-cured resin composite materials with similar base compositions, possibly leading to 131  similar bonding to the FRC-post surface. In another study, the use of these luting materials in combination with their designated adhesive system, for luting FRC posts to human teeth, revealed also no statistically significant influence of the luting system selection on the push-out bond strength (314).  6.2.1.3 Post Fit within the Luting System Groups as an Influencing Factor  The interaction of the post fit and the luting system selection was not statistically significant (p = 0.030, at α’ = 0.001). However, the post fit influenced the pull-out forces significantly, when assessing the four luting systems separately (ANOVA, p < 0.001), except when evaluating Fuji Plus (ANOVA, p > 0.001) (Table 28, p. 219 - Table 30, p. 220, Table 34, p. 221 - Table 37, p. 222, Figure 58, p. 103). For all three adhesive luting systems (RelyX Unicem, Multilink Primer/Multilink, LuxaBond/LuxaCore Z), a significant reduction in pull-out forces was detected, when comparing the congruent post fit with the incongruent post fits. No significant difference existed, when comparing the two incongruent post fits. Fuji Plus generated relatively constant pull-out forces for all three post fits. The pull-out forces, generated at a congruent post fit with Fuji Plus, RelyX Unicem and Multilink Primer/Multilink were comparable however, significantly lower compared to LuxaBond/LuxaCore Z. The pull-out forces, tested for LuxaBond/LuxaCore Z for all three posts fits exceeded all other pull-out forces, independent of the post fit. All pull-out forces of the FRC-posts, independent of the post fit, were significantly higher compared with the congruently fitting titanium post, luted with the conventional glass ionomer cement Ketac Cem (control). The failure modes differed significantly between the luting 132  systems. For Fuji Plus, the main failure was found between the luting system and the post, with an increase of failure between dentin and luting system with increasing post incongruency. The insufficient wettability, of the hydrophobic post surface with the hydrophilic glass ionomer-based material, can be discussed as a cause. With increasing cement gap width in the incongruent post fit groups, bonding to dentin seemed to decrease, possibly because of the reduced contact pressure during the post insertion. For RelyX Unicem, failure between the luting system and the dentin was found in almost 100% for all three post fit categories. The bonding to the post is superior, compared to bonding to dentin, for this material. In addition, the significant drop in pull-out forces, in combination with the failure in bonding between luting system and dentin, in the incongruent post fit groups, can be explained by the reduced contact pressure during post insertion. For this self-conditioning resin cement, an adequate contact pressure is required to allow the phosphoric acid methacrylate molecules to achieve sufficient contact with the dentinal surface and the water in the dentin to initiate surface conditioning and bonding to the calcium ions. Lack of contact pressure can lead to inferior bonding to the tooth structure (personal communication of the author with the 3M ESPE science department). The self-conditioning adhesive Multilink Primer in combination with Multilink revealed also predominant failure between luting system and dentin. For the congruent post fit, failure was also found between post and luting system (10%), while for the incongruent post fits, failure was almost exclusively found between dentin and luting system, at significantly reduced pull-out forces. This indicates that the adhesion to the post is superior compared to the adhesion to the dentin substrate. 133  LuxaBond/LuxaCore Z showed a mixed failure between luting system and dentin and luting system and post, at high pull-out forces, indicating a balanced adhesion of the luting system to the post as well as to the dentin. In the congruent post fit group, a small portion of failure within the post could be detected, which suggest the application of very high pull-out forces, exceeding the inter-laminar shear strength of the post (65-70 MPa) (546). For comparison and interpretation of the results, the literature was searched for studies on bonding properties on human or bovine teeth, using at least two of the presently investigated luting systems. Eleven studies were found (52, 56, 314, 382, 436, 437, 441, 449, 456, 467, 558). Key factors, such as: i. substrate (human (314, 382, 437, 456, 558), bovine (52, 56, 436, 441, 449, 456, 467), ii. test method (pull-out test (52, 56, 382, 436, 437, 441, 449, 456, 467)), push-out test (314, 558), iii. post insertion depth (6 mm (436), 8 mm (52, 56, 382, 437, 449, 456, 467), 10 mm (436, 449), 12 mm (441)) and iv. the tested influencing factors (luting system (52, 56, 314, 382, 436, 437, 441, 449, 456, 467, 558), post surface roughness (382), post size (437), localization (314, 558), aging (558), substrate (456), cement layer thickness (441), post surface design (56, 436), post surface pretreatment (449) and post length (436)) were identified and the results summarized in Table 4 (p.134). 134  Table 4. Overview of studies on bonding properties of FRC-posts, using at least two of the presently investigated luting systems. # = Size; CLT = Cement layer thickness; cy = Cycles; Lit = Literature reference; MPa = Mega Pascal; N = Newton; PCD = Post cavity depth; PL = Post length; PSD = Post surface design; PSR = Post surface roughness; TC = Thermal cycling; KC = Ketac Cem; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z  Lit Substrate Test (PCD) Tested Factors Luting System Dislodgement Force (N) or Bond Strength (MPa) (382) Human Pull-out at 5 mm/min (8 mm) Luting system selection, Post surface roughness (PSR) PSR Smooth Post Surface Rough Post Surface FP 8.0±1.1 10.3±1.4 RXU 10.5±2.8 10.8±2.5 MLP_ML 8.9±2.4 9.7±2.9 LB_LCZ 10.3±1.5 13.0±1.3 (437) Human Pull-out at 5 mm/min  (8 mm) Luting system selection, Post size  Post Size #3 (N) #3 (MPa) #6 (N) #6 (MPa) FP 300±50 8.8±1.5 330±50 7.7±1.4 RXU 410±60 11.9±1.8 490±140 11.4±3.3 MLP_ML 340±60 10.0±1.6 410±100 9.6±2.4 LB_LCZ 435±70 12.7±2.1 455±50 10.5±1.2 (314) Human Push-out at 0.5 mm/min Luting system selection, Localization Localization Coronal (MPa) Middle (MPa) Apical (MPa) RXU 17.2±4.7 15.8±6.8 17.3±4.1 MLP_ML 11.5±3.4 10.9±4.8 11.8±5.2 LB_LCZ 15.7±5.8 16.0±7.7 15.3±3.1 (558) Human Push-out at 0.5 mm/min Luting system selection, Aging (5000 cy TC), Localization Localization Coronal (MPa) Middle (MPa) Apical (MPa) Aging Initial TC Initial TC Initial TC RXU 14 11 10 17 11 18 MLP_ML 7 10 6 10 6 10 (456) Human Bovine Pull-out at 5 mm/min (8 mm) Luting system selection, Substrate  Substrate Human Teeth (MPa) Bovine Teeth (MPa) FP 7.9±1.3 8.6±1.5 RXU 11.0±3.0 10.4±3.4 MLP_ML 9.4±2.4 12.7±3.0 LB_LCZ 10.4±1.3 15.7±2.5 (467) Bovine Pull-out at 5 mm/min (8 mm) Luting system (aged) Luting System (MPa) KC 5.2±1.4 FP 10.4±1.6 RXU 8.8±1.6 135  Lit Substrate Test (PCD) Tested Factors Luting System Dislodgement Force (N) or Bond Strength (MPa) MLP_ML 10.6±2.2 LB_LCZ 15.2±3.2 (441) Bovine Pull-out at 0.5 mm/min (12 mm) Luting system selection, Cement layer thickness (CLT) CLT CLT 1 (congruent) (N) CLT 2 (incongruent) (N) RXU 530.5±95.4 573.6±71.6 MLP_ML 407.8±73.2 457.5±115.35  (52) Bovine Pull-out at 5 mm/min (8 mm) Luting system Luting System (MPa) KC 4.0±1.1 FP 8.3±1.4 RXU 12.0±3.0 MLP_ML 10.6±2.7 LB_LCZ 14.8±2.3 (56) Bovine Pull-out at 5 mm/min (8 mm) Luting system, Post surface design (PSD) PSD Smooth Post (MPa) Macro-Lock Post (MPa) KC 4.2±1.0 7.2±2.2 FP 8.6±1.5 13.4±2.5 RXU 10.4±3.4 9.2±2.9 MLP_ML 12.7±3.0 12.5±4.5 LB_LCZ 15.7±2.5 20.6±2.2 (449) Bovine  Pull-out at 5 mm/min (10 mm) Luting system, Post pre-treatment (PPT) PPT Ethanol (MPa) Ethanol + Adhesive (MPa) MLP_ML 13.1±3.0 15.0±2.9 LB_LCZ 13.9±2.3 14.6±2.5 (436) Bovine Pull-out at 5 mm/min (6 and 10 mm) Luting system, Post surface design (PSD), Post length (PL) PSD Smooth Post (MPa) Macro-Lock Post (MPa) PL (mm) 6 (N) 10 (N) 6 (N) 10 (N) FP 132.4±29.9 287.6±50.9 251.8±30.4 478.4±45.1 RXU 196.1±62.8 357.4±151.3 263.2±47.4 571.7±115.1 MLP_ML 399.6±64.3 724.4±92.7 428.7±78.1 754.1±97.7 LB_LCZ 432.2±33.7 841.5±64.4 509.1±40.3 935.6±57.6 PL (mm) 6 (MPa) 10 (MPa) 6 (MPa) 10 (MPa) FP 4.2±0.9 5.1±0.9 8.0±1.0 8.5±0.8 RXU 6.3±2.0 6.4±2.7 8.4±1.5 10.2±2.1 MLP_ML 12.7±2.0 12.9±1.7 13.7±2.5 13.5±1.7 LB_LCZ 13.8±1.1 15.0±1.1 16.2±1.3 16.7±1.0 136  When evaluating the data from Table 4 (p. 134) per luting system, a wide range of the dislodgement forces and bond strengths was found (Table 5, p. 136). The main factors, responsible for the wide range, were identified as: i. post insertion length, ii. post surface design, iii. surface roughness and iv. substrate. The data of the present study lay within the dislodgement force range from these previous studies (Fuji Plus (427 – 456 MPa), RelyX Unicem (352 – 447 MPa), Multilink Primer/Multilink (327 – 458 MPa), LuxaBond/LuxaCore Z (484 – 610 MPa)) (436, 437, 441).  Table 5. Overview of bond strength and dislodgement force ranges for FRC-posts, luted with Fuji Plus, RelyX Unicem, Multilink Primer/Multilink or LuxaBond/LuxaCore Z, achieved in different studies (52, 56, 314, 382, 436, 437, 441, 449, 456, 467, 558).   Luting System Pull-out Test Push-out Test BS-Range (MPa) DLF-Range (N) BS-Range (MPa) KC 4.2 – 5.2 No data No data FP 4.2 – 13.4 132 – 480 No data RXU 6.3 – 12.0 196 – 537 10.0 – 17.3 MLP_ML 6.0 – 15.0 340 – 745 6.0 – 11.8 LB_LCZ 10.3 – 20.6 432 - 935 15.3 – 16.0  Two of the previous studies were using the same post system and luting systems on bovine teeth as the present study (Macro-Lock Post Illusion X-RO) (56, 436). In both studies, LuxaBond/LuxaCore Z achieved significantly higher bond strength, compared to the other three luting systems. These findings are in agreement with the results of our study. In one of the previous studies (56), Fuji Plus performed similar as in the present study, followed by Multilink Primer/Multilink and RelyX Unicem. In the second study (436), the performance of LuxaBond/LuxaCore Z, RelyX Unicem and Multilink Primer/Multilink was comparable with the present study 137  while the results for Fuji Plus were considerably lower. This can be possibly explained with the lack of dentin conditioning, using Fuji Plus Conditioner. The comparison of these two previous studies revealed general similarities with the present results. However, variations in study design and influencing factors are likely responsible for some differences.  One previous study (456) was evaluating the bond strength of the four luting materials in combination with a smooth surface post on bovine and human teeth. The comparison of the results between the two substrates showed differences in the ranking of the luting systems, depending on the achieved bond strength. In bovine teeth, LuxaBond/LuxaCore Z achieved the highest bond strength, followed by Multilink Primer/Multilink, Rely X Unicem and Fuji Plus. In human teeth, RelyX Unicem and LuxaBond/LuxaCore Z generated the highest bond strength, followed by Multilink Primer/Multilink and Fuji Plus. The discrepancies in ranking for Fuji Plus, compared to the present study, can be explained with the smooth post surface. The macro-retentive post design of the Macro-Lock Post Illusion X-RO was found to be very beneficial for the bonding properties of Fuji Plus in order to overcome the adhesion problems by mechanical linkage (56). The discrepancies in ranking for the luting systems between bovine and human teeth for RelyX Unicem and LuxaBond/LuxaCore Z were also noticeable when comparing studies on human teeth (314, 382, 437, 456) with studies on bovine teeth (52, 56, 436, 467). The variations can be explained with the differences in the dentinal structure, namely larger tubule diameter and higher tubule density in bovine root canal dentin, compared to human teeth (496, 499). The bond strength, achieved with the Etch & Rinse adhesive 138  LuxaBond and the resin cement LuxaCore Z in bovine teeth, compared to human teeth were possibly higher because of the generation of multiple, large and deeply inserting resin tags. The bond strengths, achieved with RelyX Unicem, were likely lower in bovine teeth because of the smaller inter-tubular dentin surface area, compared to human teeth.  Considering all these factors, it can be concluded that the post fit influenced the bonding properties of all three resin-based luting materials. Based on the present study, the by far best results were achieved in bovine teeth with LuxaBond/LuxaCore Z. However, the interpretation of these results should be conservative, since comparative data between human and bovine teeth showed a similar performance of RelyX Unicem and LuxaBond/LuxaCore in human teeth. It can be hypothesized that both of these materials would be feasible, when restoring human teeth with incongruently fitting posts. However, further studies on human teeth should be conducted to prove this hypothesis. 139  Chapter 7: Conclusion The present study is part of a comprehensive project, which is designed to propose clinical guidelines for the restoration of endodontically treated immature teeth. These teeth are structurally week and prone to cervical fractures. Various studies have focused on the suitability of reinforcement methods to increase the fracture resistance of endodontically treated immature teeth. Adhesively luted FRC-posts or fiber-reinforced composite materials were identified to achieve the best results. Using prefabricated FRC-posts in immature teeth often results in an incongruent post fit because commercially available posts are smaller in diameter than the root canal. Information on the bonding performance of conventional and adhesive luting systems, in combination with FRC-posts with incongruent post fit, is scarce. The aim of the present study was to evaluate the influence of the post fit and the luting system, when using FRC-posts with a macro-retentive surface design in simulated immature bovine teeth. Previous studies of our group, as part of the main project, have proven the superior performance of the luting materials and the post system, used in the present study.   Within the limitation of the present ex vivo study on simulated immature teeth, using bovine teeth, it can be concluded that: 1. The post fit, irrespective of the luting system, influences the pull-out force of conventionally and adhesively luted quartz fiber-reinforced composite posts. Therefore, the hypothesis was rejected. The posts with the congruent fit achieved 140  significantly higher pull-out forces than the posts with the two incongruent post fits. The failure mode for the tree post fit categories was not significantly different.  2. The luting system type, irrespective of the post fit, influences the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts. Therefore, the hypothesis was rejected. The Etch & Rinse adhesive LuxaBond in combination with the resin luting material LuxaCore Z achieved significantly higher pull-out forces than the three other tested materials. All four materials, used for FRC-post insertion, achieved significantly higher pull-out forces than the control group, represented by a congruently fitting titanium post, luted with glass ionomer cement. 3. An interaction between post fit and luting system type, which influences the pull-out force and the failure mode of conventionally and adhesively luted quartz fiber-reinforced composite posts, was not found. The hypothesis was accepted.  4. The post fit influences the pull-out force and the failure mode of quartz fiber-reinforced composite posts, luted with adhesive, resin-based luting systems. Therefore, the hypothesis, specifically for these three materials, was rejected. The pull-out forces for all three adhesive, resin-based luting materials were significantly higher for the congruent post fit. The pull-out forces for LuxaBond/LuxaCore Z, for all three pots-fit categories were significantly higher than the values of all remaining groups.  5. The post fit does not influence the pull-out force and the failure mode of quartz fiber-reinforced composite posts, luted with the conventional resin-reinforced glass ionomer cement Fuji Plus. The hypothesis, for this material, was accepted. 141   In order to achieve the overall goal to propose guidelines for the restoration of endodontically treated immature teeth and based on pervious and the present findings, further research will be conducted to assess the following:  Influence of the apexification method on the fracture resistance of endodontically treated immature teeth (simulated immature bovine teeth) (ex vivo),  Influence of the post fit and luting system under simulated clinical conditions (human immature teeth, chewing simulation and thermal cycling) (ex vivo),  Influence of apexification and restoration method on the fracture resistance of endodontically treated immature teeth under simulated clinical conditions (human immature teeth, chewing simulation and thermal cycling) (ex vivo),  Influence of apexification and restoration method on the fracture resistance of endodontically treated immature teeth under clinical conditions (multi-center clinical in vivo study).  142  Bibliography	1. 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ALST  Step Etch & Rinse Adhesive + Resin Cement Self-conditioning Adhesive + Resin Cement Self-conditioning Resin Cement Conditioning  Phosphoric acid etching, rinsing with water  Removal of smear layer and of inorganic components with exposure of collagen fibers  Two- or one step adhesive (one or two bottles)  Mild to strong organic acids included in the adhesive, no separate rinsing step  Dissolution of the smear layer and superficial dentin with exposure of the collagen fibers, the inorganic components remain in the adhesive  Hydrophobization of the collagen fibers, penetration of the collagen network, hybrid layer generation   Phosphoric acid ester incorporated in resin cement  Dissolution of the smear layer and superficial dentin with exposure of the collagen fibers, the inorganic components remain in the resin cement  Hydrophobization of the collagen fibers, penetration of the collagen network, hybrid layer generation  Bonding  Multi-step adhesive or one-Step adhesive (one bottle, two bottles)  Hydrophobization of the collagen fibers, penetration of the collagen network, hybrid layer generation Luting  Resin cement  Bonding of the resin cement to the adhesive surface  Resin cement   Bonding of the resin cement to the adhesive surface      210  Table 7. Material specific data (manufacturer’s information) for Macro-LockTM Post Illusion X-RO (sizes 1, 3 and 6) (RTD, Saint-Égrève, France)  Characteristics  Data Composition Pre-stretched silanizied quartz fibers, epoxy resin matrix Fiber Weight >60 % Fiber Volume 80 % Length 17.5 mm Diameter Size 1 D1 (tip) 0.80 mm D2 (end) 1.35 mm Size 3 D1 (tip) 1.00 mm  D2 (end) 1.67 mm  Size 6 D1 (tip) 1.30 mm D2 (end) 2.22 mm Geometry Conical-cylindrical with spiral retention groves Surface Roughness Rz 5.48, Ra 0.82 Color Translucent at body temperature, colored at room temperature (size 1 yellow, size 3 blue, size 6 white)  Radiopacity 340% of Aluminum equivalent Flexural Strength 1800-2000 MPa Modulus of Elasticity 15 GPa Interlaminate Shear Strength 65-70 MPa Conditioning Cleaning with alcohol (70%), conditioning with respective luting system adhesive LOT 116900909  Table 8. Material specific data (manufacturer’s information) for RPR Prototype Titanium Post (NTI GmbH, Kahla, Germany)  Characteristics Data Composition Pure Titanium Length 25.0 mm Diameter D1 (tip) 1.1 mm D2 (end) 2.2 mm Geometry Conical-cylindrical  Surface Roughness Rz 5.38, Ra 0.79 Color Grey titanium Radiopacity Yes, nor further information Modulus of Elasticity 105 GPa Conditioning Cleaning with alcohol (70%) LOT U10.001    211  Table 9. Material specific data (manufacturer’s information) for KetacTM Cem Aplicap (3M ESPE, Seefeld, Germany)  Material Characteristics Composition Curing Mode LOT KetacTM Cem Aplicap powder Conventional glass ionomer cement Glass powder, pigments,  Chemical 423183 KetacTM Cem Aplicap fluid Polyethylene, water, polycarbonic acid, tartaric acid, preservative, acid  Table 10. Material specific data (manufacturer’s information) for Fuji PlusTM Capsule (GC Europe, Leuven, Belgium)  Material Characteristics Composition Curing Mode LOT Fuji Plus™ Conditioner Dentin etching and sealing of dentinal tubules Citric acid (10%), distilled water (87%), iron (III) chloride (3%), Brilliant blue FCF None 1008231 Fuji Plus™ powder Resin-reinforced glass ionomer cement Aluminosilicate glass Chemical 1008171 Fuji Plus™ fluid Polyacrylic acid, distilled water, hydroxyethyl-methacrylate, urethanedimethacrylate   Table 11. Material specific data (manufacturer’s information) for RelyXTM Unicem A2 (3M ESPE, Seefeld, Germany) Material Characteristics Composition Curing Mode LOT RelyXTM Unicem powder Self-conditioning adhesive resin cement Silanized glass powder, silanized silicic acid, pyrimidine, calcium hydroxide, peroxide compounds, pigments Dual 424045 RelyXTM Unicem fluid Methacrylated phosphoric acid esters, dimethacrylate, stabilizer, triethylene glycol dimethacrylate, acetate, initiator   212  Table 12. Material specific data (manufacturere’s information) Multilink® Automix und Multilink® Primer A/B Light (Ivoclar Vivadent, Schaan, Liechtenstein)  Material Characteristics Composition Curing Mode LOT Multilink® Primer A Self-conditioning adhesive N,N-Bis(2-hydroxyethyl)-P-toluidine Dual P63825 Multilink® Primer B Phosphoric acid acrylate, 2-Hydroxyethylmeth-acrylat, modified methacrylate resin Multilink® Automix  Resin cement Dimethacrylate, 2-Hydroxyethylmeth-acrylat, Bis-GMA, urethane dimethacrylate, dibenzoylperoxide, ytterbium, barium glass, trifluoride Chemical curing with optional light curing N69998  Table 13. Material specific data (manufacturere’s information) Etching Gel, LuxaBond® Pre-Bond, LuxaBond® Bond A/B und LuxaCore® Z  (DMG, Hamburg, Germany)  Material Characteristics Composition Curing Mode LOT Etching Gel Dentin etching Phosphoric acid (37%), pyrogenic silicic acid None 626113 LuxaBond® Pre-Bond Curing enhancer Salts, ethanol, arylsulfinate solution None 722060 LuxaBond® Bond A Adhesive Aromatic dimethacrylate, monomethylacrylate, catalyst Dual 722060 LuxaBond® Bond B Aromatic dimethacrylate, monomethacrylate, dimethacrylate, carboxylmethacrylate, benzoyl peroxide 722060 LuxaCore® Z Resin cement Barium glass, pyrogenic silicid acid, nano fillers, silicium oxide, zirconium oxide, bis-GMA, urethane dimethacrylate, aliphatic dimethacrylate, aromatic dimethacrylate Dual 687563   213  Table 14. Instructions for post insertion of the RPR Prototype Titanium Post with KetacTM Cem Aplicap (based on manufacturer’s instructions)  Luting System Pretreatment Root Canal  Pretreatment Post Post Insertion Procedure KetacTM Cem Aplicap  Irrigate with distilled water  Dry with air, using the air-water syringe with a Suction Needle 20 ga (Transcodent)   Clean with ethanol (70 %)  Dry with air, using the air-water syringe with a Suction Needle 20 ga   Activate capsule (2 s)  Mix capsule for 10 s (RotomixTM Capsule Mixing Unit, 3M ESPE)  Roll post in a cement reservoir on a mixing pad  Fill post cavity completely with cement, using AccuDose® Needle Tubes 20 ga   Insert post slowly into the post cavity to allow excess cement to exit coronally  Let cement set in the incubator (7 min, 37°C)  Table 15. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with Fuji Plus™ Capsule (based on manufacturer’s instructions)  Luting System Pretreatment Root Canal  Pretreatment Post Post Insertion Procedure Fuji Plus™ Conditioner  Fuji Plus™ Capsule  Irrigate with distilled water  Apply the conditioner with EndoBrush (DMG) and etch (20 s)   Irrigate with distilled water (20 s)   Dry with air, using the air-water syringe with a Suction Needle 20 ga   Clean with ethanol (70 %)  Dry with air, using the air-water syringe with a Suction Needle 20 ga   Shake capsule to loosen the powder up  Activate capsule (2 s)  Mix capsule (10 s) (RotomixTM Capsule Mixing Unit, 3M ESPE)  Roll post in a cement reservoir on a mixing pad  Fill post cavity completely with cement, using AccuDose® Needle Tubes 20 ga   Insert post slowly into the post cavity to allow excess cement to exit coronally  Let cement set in the incubator (4 min, 37°C)   214  Table 16. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with RelyXTM Unicem Aplicap (based on manufacturer’s instructions)  Luting System Pretreatment Root Canal  Pretreatment Post Post Insertion Procedure RelyXTM Unicem Aplicap  Irrigate with distilled water  Dry gently with air, using the air-water syringe with a Suction Needle 20 ga, leaving the dentin slightly moist  Clean with ethanol (70 %)  Dry with air, using the air-water syringe with a Suction Needle 20 ga  Activate capsule (2 s)  Mix capsule (10 s) (RotomixTM Capsule Mixing Unit, 3M ESPE)  Roll post in a cement reservoir on a mixing pad  Fill post cavity completely with resin cement, using Elongation Tip  Insert post slowly into the post cavity to allow excess cement to exit coronally  Light cure (Curing Light, KaVo) (20s, 600 mW/cm2)   Let cement set in the incubator (5 min, 37°C)  Table 17. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with Multilink® Primer/Multilink® Automix (based on manufacturer’s instructions)  Luting System Pretreatment Root Canal  Pretreatment Post Post Insertion Procedure Multilink® Primer  Multilink® Automix  Irrigate with distilled water  Dry with air, using the air-water syringe with a Suction Needle 20 ga   Mix Primer A and B (1:1) (5s)  Apply mixture with EndoBrush (15 s)   Dry with air, using the air-water syringe with a Suction Needle 20 ga   Clean with ethanol (70 %)  Dry with air, using the air-water syringe with a Suction Needle 20 ga  Apply adhesive mixture with Micro Applicator (15 s)   Dry with air, using the air-water syringe with a Suction Needle 20 ga   Roll post in a cement reservoir on a mixing pad  Fill post cavity completely with resin cement, using Endotip   Insert post slowly into the post cavity to allow excess cement to exit coronally  Light cure (40s, 600 mW/cm2)   Let cement set in the incubator (5 min, 37°C)  215  Table 18. Instructions for post insertion of the Macro-LockTM Post Illusion X-RO with LuxaBond®/LuxaCore® Z Automix (based on manufacturer’s instructions)  Luting System Pretreatment Root Canal  Pretreatment Post Post Insertion Procedure LuxaBond®   LuxaCore® Z Automix  Irrigate with distilled water  Dry with air, using the air-water syringe with a Suction Needle 20 ga  Fill post cavity completely with Etching Gel and etch (15 s)  Irrigate with distilled water (20 s)   Dry with air, using the air-water syringe with a Suction Needle 20 ga  Apply distilled water with EndoBrush for rewetting  Apply PreBond with EndoBrush  Mix Primer A and B (1:1) (5s)  Apply mixture with EndoBrush (20 s)   Dry with air, using the air-water syringe with a Suction Needle 20 ga   Clean with ethanol (70 %)  Dry with air, using the air-water syringe with a Suction Needle 20 ga  Apply PreBond with Micro Applicator (15 s)   Apply adhesive mixture with Micro Applicator (20 s)   Dry with air, using the air-water syringe with a Suction Needle 20 ga   Roll post in a cement reservoir on a mixing pad  Fill post cavity completely with resin cement, using Endotip   Insert post slowly into the post cavity to allow excess cement to exit coronally  Light cure (10s, 600 mW/cm2)   Let cement set in the incubator (5 min, 37°C)     216  Table 19. P-values for Kolmogov-Smirnov test of normal distribution of the pull-out force data, subdivided by post fit. All data were normally distributed.  Post Fit P-value  Congruency 0.384 Medium Incongruency 0.691 High Incongruency 0.807  Table 20. P-values for Kolmogov-Smirnov test of normal distribution of the pull-out force data, subdivided by luting system. All data were normally distributed  Luting System P-value Fuji Plus 0.981 RelyX Unicem 0.999 Multilink Primer/Multilink 0.373 LuxaBond/LuxaCore Z 0.990  Table 21. P-values for Kolmogov-Smirnov test of normal distribution of the pull-out force data, subdivided by luting system and post fit. All data were normally distributed.                               Post Fit  Luting System P-value  Congruency Medium Incongruency High Incongruency Fuji Plus 0.394 0.534 0.958 RelyX Unicem 0.920 0.482 0.809 Multilink Primer/Multilink 0.981 0.800 0.387 LuxaBond/LuxaCore Z 0.882 0.962 0.303            217  Table 22. Descriptive data for the pull-out force, subdivided by the post fit.  SD = Standard deviation; IQR = Interquartile range; CFV = Cofactor of variation   Pull-out force [N] Congruency Medium Incongruency High Incongruency Mean 436.6 426.0 397.5 Median 440.7 433.8 406.5 Variance 22106.6 10428.8 8058.5 SD 148.7 102.1 89.8 Minimum 156.9 248.11 232.3 Maximum 748.85 688.5 590.0 IQR 188.93 145.5 119.0 CFV 34.1 24.0 22.6  Table 23. Descriptive data for the failure mode analysis, subdivided by the post fit.  SD = Standard deviation; C = Congruent; MIC = Medium incongruency; HIC = High incongruency  Post size F_D [%] F_D_LS [%] F_LS [%] F_LS_P [%] F_P [%] Mean SD Mean SD Mean SD Mean SD Mean SD C 0 0 64.2 41.6 0.2 0.7 35.5 41.1 0.1 1.3 MIC 0 0 70.7 43.2 0 0 29.3 43.2 0 0 HIC 0 0 65.8 45.9 0 0 34.2 45.9 0 0  Table 24. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits.  The local significance level was adjusted with the Bonferroni-correction procedure (α’ = α/3 = 0.017). The fields highlightened in yellow represent statistically significant differences (p < 0.017). C = Congruent; MIC = Medium incongruency; HIC = High incongruency     C MIC HIC   < 0.001 < 0.001 C   0.048 MIC   HIC 218  Table 25. Descriptive data for the pull-out force, subdivided by the post fit.  SD = Standard deviation; IQR = Interquartile range; CFV = Cofactor of variation   Pull-out force [N] KC_co FP RXU MLP_ML LB_LCZ Mean 211.2 441.2 390.7 379.3 544.0 Median 207.2 439.7 392.6 364.2 539.5 Variance 1231.4 2019.0 6479.3 11400.5 9334.4 SD 35.1 44.9 80.5 106.8 96.6 Minimum 156.9 337.8 232.29 243.7 353.2 Maximum 277.8 549.7 590.3 660.6 748.9 IQR 61.0 63.6 112.9 161.8 134.9 CFV 16.6 10.2 20.6 28.2 17.8   Table 26. Descriptive data for the failure mode analysis, subdivided by the luting system.  SD = Standard deviation; KC_co = Ketac Cem (control group); FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z  Luting system F_D [%] F_D_LS [%] F_LS [%] F_LS_P [%] F_P [%] Mean SD Mean SD Mean SD Mean SD Mean SD KC_co 0 0 61.5 18.6 0 0 38.5 18.6 0 0 FP 0 0 7.7 21.9 0 0 92.3 21.9 0 0 RXU 0 0 99.5 1.5 0 0 0.5 1.5 0 0 MLP_ML 0 0 95.8 16.5 0 0 4.1 16.4 0.1 0.2 LB_LCZ 0 0 65.5 43.4 0.3 1.0 33.8 42.5 0.4 1.7  Table 27. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different luting systems.  The local significance level was adjusted with the Bonferroni-correction procedure (α’ = α/6 = 0.008). The fields highlightened in yellow represent statistically significant differences (p < 0.008). FP = Fuji Plus: RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z  FP RXU MLP_ML LB_LCZ   0.002 < 0.001 < 0.001 FP   1.000 < 0.001 RXU   < 0.001 MLP_ML   LB_LCZ    219  Table 28. Descriptive data for the pull-out force, subdivided by the luting system for the congrunet post fit.  SD = Standard deviation; IQR = Interquartile range; CFV = Cofactor of variation; KC_co = Ketac Cem (control group); FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z   Pull-out force [N] KC_CO FP RXU MLP_ML LB_LCZ Mean 211.2 456.1 447.3 458.5 609.8 Median 207.2 441.4 449.0 446.3 621.9 Variance 1232.5 3081.1 3534.7 12290.7 8948.9 SD 35.1 55.5 59.4 110.9 94.6 Minimum 156.9 375.1 334.5 259.1 392.5 Maximum 277.8 549.7 590.3 660.6 748.8 IQR 61.0 104.75 73.9 154.2 124.2 CFV 16.6 12.2 13.3 24.2 15.5  Table 29. Descriptive data for the pull-out force, subdivided by the luting system for the medium incongruent post fit.  SD = Standard deviation; IQR = Interquartile range; CFV = Cofactor of variation; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z   Pull-out force [N] FP RXU MLP_ML LB_LCZ Mean 440.6 373.1 352.4 538.1 Median 450.9 357.1 343.5 535.3 Variance 1745.4 6171.4 6747.2 6588.4 SD 41.8 78.6 82.1 81.2 Minimum 337.8 290.5 248.1 371.9 Maximum 498.0 550.5 500.9 688.5 IQR 53.0 94.5 140.0 114.6 CFV 9.5 21.1 23.3 15.1      220  Table 30. Descriptive data for the pull-out force, subdivided by the luting system for the high incongruent post fit.  SD = Standard deviation, IQR = Interquartile range, CFV = Cofactor of variation; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z   Pull-out force [N] FP RXU MLP_ML LB_LCZ Mean 426.9 351.8 327.2 484.0 Median 426.0 367.7 300.5 512.7 Variance 995.9 5121.6 6130.8 5061.4 SD 31.6 71.6 78.3 71.1 Minimum 376.4 232.3 243.7 353.2 Maximum 486.4 444.9 514.4 590.0 IQR 52.02 143.9 103.2 120.1 CFV 7.4 20.4 23.9 9.0  Table 31. Descriptive data for the failure mode analysis, subdivided by the luting system for the congrunet post fit. SD = Standard deviation; KC_co = Ketac Cem (control group); FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z  Luting system F_D [%] F_D_LS [%] F_LS [%] F_LS_P [%] F_P [%] Mean SD Mean SD Mean SD Mean SD Mean SD KC_co 0 0 61.5 18.6 0 0 38.5 18.6 0 0 FP 0 0 0.6 1.6 0 0 99.4 1.6 0 0 RXU 0 0 99.6 1.3 0 0 0.4 1.3 0 0 MLP_ML 0 0 89.2 27.6 0 0 10.7 27.4 0.1 0.4 LB_LCZ 0 0 70.2 40.3 0.8 1.6 27.8 37.0 1.2 2.7  Table 32. Descriptive data for the failure mode analysis, subdivided by the luting system for the medium incongrunet post fit. SD = Standard deviation; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z  Luting system F_D [%] F_D_LS [%] F_LS [%] F_LS_P [%] F_P [%] Mean SD Mean SD Mean SD Mean SD Mean SD FP 0 0 10.2 22.7 0 0 89.8 22.7 0 0 RXU 0 0 99.8 1.1 0 0 0.2 1.1 0 0 MLP_ML 0 0 100.0 100.0 0 0 0 0 0 0 LB_LCZ 0 0 72.8 40.1 0 0 27.2 40.1 0 0 221  Table 33. Descriptive data for the failure mode analysis, subdivided by the luting system for the high incongrunet post fit. SD = Standard deviation; FP = Fuji Plus; RXU = RelyX Unicem; MLP_ML = Multilink Primer/Multilink; LB_LCZ = LuxaBond/LuxaCore Z  Luting system F_D [%] F_D_LS [%] F_LS [%] F_LS_P [%] F_P [%] Mean SD Mean SD Mean SD Mean SD Mean SD FP 0 0 12.3 29.8 0 0 87.7 29.8 0 0 RXU 0 0 99.1 1.9 0 0 0.9 1.9 0 0 MLP_ML 0 0 98.2 3.9 0 0 1.8 3.9 0 0 LB_LCZ 0 0 53.6 48.9 0 0 46.4 48.9 0 0  Table 34. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for Fuji Plus.  The local significance level was adjusted with the Bonferroni-correction procedure (α’ = α/12 = 0.004. C = Congruent; MIC = Medium incongruency; HIC = High incongruency   Table 35. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for RelyX Unicem.  The local significance level was adjusted with the Bonferroni-correction procedure (α’ = α/12 = 0.004). The fields highlightened in yellow represent statistically significant differences (p < 0.004). C = Congruent; MIC = Medium incongruency; HIC = High incongruency      C MIC HIC   0.513 0.217 C   0.561 MIC   HIC C MIC HIC   0.002 < 0.001 C   0.368 MIC   HIC 222  Table 36. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for Multilink Primer/Multilink.  The local significance level was adjusted with the Bonferroni-correction procedure (α’ = α/12 = 0.004). The fields highlightened in yellow represent statistically significant differences (p < 0.004). C = Congruent; MIC = Medium incongruency; HIC = High incongruency   Table 37. P-values for pairwise comparison of the pull-out force data (Dunnett T3-test) for the different post fits, specifically for LuxaBond/LuxaCore Z.  The local significance level was adjusted with the Bonferroni-correction procedure (α’ = α/12 = 0.004). The fields highlightened in yellow represent statistically significant differences (p < 0.004). C = Congruent; MIC = Medium incongruency; HIC = High incongruency  	C MIC HIC   < 0.001 < 0.001 C   0.285 MIC   HIC C MIC HIC   0.003 < 0.001 C   0.022 MIC   HIC 

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