Dentistry, Faculty of
DSpace
UBCV
Fedorova, Ksenia
Master of Science - MSc
University of British Columbia
Introduction: Calcium hydroxide removal from internal inflammatory root resorptions (IRR) is challenging and many different irrigation techniques have been proven ineffective in clearing this medicament completely. Objective: The aim of this study was to compare the effectiveness of different irrigation methods in removing calcium hydroxide in the 3D printed molar tooth model including deep and shallow internal resorptions. Hypotheses: The presence, depth and location of resorption, irrigation method and composition of calcium hydroxide (Ca(OH)₂) do not affect the effectiveness of Ca(OH)₂ removal by different irrigation devices. Methods: 3D printed transparent models with artificial IRR cavities were designed, printed and filled with UltraCal XS or Multi-Cal calcium hydroxide paste. Apices and side vents were sealed with SoundSeal material. Open-ended needle irrigation (ONI) at 5 ml/L and 15 ml/min, double-side-vented needle irrigation (DNI) at 5 ml/min, EndoActivator (EA), PiezoFlow (PF) at 15 ml/min and GentleWave system (GW) with distilled water as irrigant were used to remove Ca(OH)₂ from the root canal system and resorptions at manufacturer recommended maximum irrigation times. 36 groups (n=10) were established. Ca(OH)₂ removal was assessed visually under 4.2 x magnification on dental operating microscope (DOM). The data were statistically analyzed by Chi-Square, Fisher’s exact test, independent t-test and binary logistic regression analysis, with the significance level set at 5%. Results: Bivariate analyses found statistically significant outcome associations with presence, location and depth of resorption, type of irrigation and type of Ca(OH)₂. Binary logistic regression models showed that Ca(OH)₂ removal was associated with four predictors: type of Ca(OH)₂ (OR = 2.022; 95% CI, 1.245 – 3.285), use of GW as irrigation method (OR = 99.502; 95% CI, 44.928-202.348), location of resorption (OR = 1.441; 95% CI, 1.082 – 1.918) and reverse resorption type (OR = 8.774; CI = 95%, 4.988 – 15.402). Overall, GW was the greatest predictor of effective Ca(OH)₂ removal, followed by absence of resorptions, use of Multi-Cal and coronal location of resorption. Conclusions: GentleWave was more effective in removing Ca(OH)₂ from deep and shallow resorptions than other irrigation methods. Removal of Ca(OH)₂ was affected by the presence, depth and location of resorption and type of Ca(OH)₂.
EFFECTIVENESS OF DIFFERENT IRRIGATION PROTOCOLS IN REMOVING CALCIUM HYDROXIDE FROM SIMULATED INTERNAL ROOT RESORPTIONS by Ksenia Fedorova BDent (Hons), The University of Sydney, 2011 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Craniofacial Science) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) July 2022 © Ksenia Fedorova, 2022 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis entitled: Effectiveness of different irrigation protocols in removing calcium hydroxide from simulated internal root resorptions submitted by Ksenia Fedorova in partial fulfillment of the requirements for the degree of Master of Science in Craniofacial Science Examining Committee: Dr. Markus Haapasalo, Professor, Department of Oral Biological & Medical Sciences, UBC. Supervisor Dr. Ya Shen, Professor, Department of Oral Biological & Medical Sciences, UBC. Supervisory Committee Member Dr. Ahmed Hieawy, Clinical Associate Professor, Department of Oral Biological & Medical Sciences, UBC. Supervisory Committee Member Dr. Ricardo M. Carvalho, Professor, Department of Oral Biological & Medical Sciences, UBC. Additional Examiner iii Abstract Introduction: Calcium hydroxide removal from internal inflammatory root resorptions (IRR) is challenging and many different irrigation techniques have been proven ineffective in clearing this medicament completely. Objective: The aim of this study was to compare the effectiveness of different irrigation methods in removing calcium hydroxide in the 3D printed molar tooth model including deep and shallow internal resorptions. Hypotheses: The presence, depth and location of resorption, irrigation method and composition of calcium hydroxide (Ca(OH)2) do not affect the effectiveness of Ca(OH)2 removal by different irrigation devices. Methods: 3D printed transparent models with artificial IRR cavities were designed, printed and filled with UltraCal XS or Multi-Cal calcium hydroxide paste. Apices and side vents were sealed with SoundSeal material. Open-ended needle irrigation (ONI) at 5 ml/L and 15 ml/min, double-side-vented needle irrigation (DNI) at 5 ml/min, EndoActivator (EA), PiezoFlow (PF) at 15 ml/min and GentleWave system (GW) with distilled water as irrigant were used to remove Ca(OH)2 from the root canal system and resorptions at manufacturer recommended maximum irrigation times. 36 groups (n=10) were established. Ca(OH)2 removal was assessed visually under 4.2 x magnification on dental operating microscope (DOM). The data were statistically analyzed by Chi-Square, Fisher’s exact test, independent t-test and binary logistic regression analysis, with the significance level set at 5%. Results: Bivariate analyses found statistically significant outcome associations with presence, location and depth of resorption, type of irrigation and type of Ca(OH)2. Binary logistic iv regression models showed that Ca(OH)2 removal was associated with four predictors: type of Ca(OH)2 (OR = 2.022; 95% CI, 1.245 – 3.285), use of GW as irrigation method (OR = 99.502; 95% CI, 44.928-202.348), location of resorption (OR = 1.441; 95% CI, 1.082 – 1.918) and reverse resorption type (OR = 8.774; CI = 95%, 4.988 – 15.402). Overall, GW was the greatest predictor of effective Ca(OH)2 removal, followed by absence of resorptions, use of Multi-Cal and coronal location of resorption. Conclusions: GentleWave was more effective in removing Ca(OH)2 from deep and shallow resorptions than other irrigation methods. Removal of Ca(OH)2 was affected by the presence, depth and location of resorption and type of Ca(OH)2. v Lay Summary Teeth with internal inflammatory root resorptions (IRR) require irrigation and placement of calcium hydroxide medicament to aid in successful disinfection of their complex anatomy. After calcium hydroxide has adequate time to work inside the tooth, it is important to fully remove it for the root canal filling to be well sealed. Traditional methods of irrigation have often been unsuccessful in removing calcium hydroxide from teeth with IRR and more advanced irrigation techniques are commonly used. This study compared syringe needle irrigation, sonic, ultrasonic and multisonic irrigation systems in their ability to effectively remove calcium hydroxide from resorptions and root canal system in a 3D printed tooth model. The findings showed that the multisonic irrigation system was more effective than other methods of irrigation in removing calcium hydroxide from root canal system and resorptions. It was also demonstrated that multiple aspects of the resorption affected how easily the medicament was removed. vi Preface This thesis is the original and unpublished work of Dr. Ksenia Fedorova, as per requirements of Master of Science in Craniofacial Science and Diploma in Endodontics. The research question was developed by Dr. Ksenia Fedorova with assistance of Dr. Markus Haapasalo. The 3D model was designed by Dr. Markus Haapasalo, Dr. Abdullah AlMegbel, Dr. Jack Liu and modified by Dr. Ksenia Fedorova and Dr. Ahmed Hieawy. All experimental data was collected by Dr. Ksenia Fedorova with laboratory assistance provided by Dr. Ahmed Hieawy and Dr. Abdullah AlMegbel. Statistical analysis and interpretation of data was performed by Dr. Ksenia Fedorova with support from Dr. Jolanta Aleksejuniene. Manuscript composition was carried out by Dr. Ksenia Fedorova with editing by Dr. Markus Haapasalo. The relative contribution to this research project by Dr Ksenia Fedorova was 85%. vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ........................................................................................................................ vii List of Tables ..................................................................................................................................x List of Figures ............................................................................................................................... xi List of Abbreviations ................................................................................................................. xiii Acknowledgements ......................................................................................................................xv Dedication .................................................................................................................................. xvii Chapter 1: Review of the literature ..............................................................................................1 1.1 Internal inflammatory root resorption ............................................................................. 1 1.1.1 Etiology and pathogenesis ...................................................................................... 1 1.1.2 Presentation and clinical findings ........................................................................... 2 1.1.3 Treatment challenges .............................................................................................. 2 1.2 Calcium hydroxide .......................................................................................................... 3 1.2.1 Benefits of using calcium hydroxide in IRR ........................................................... 3 1.2.2 Consequences of incomplete calcium hydroxide removal ...................................... 4 1.3 Methods of irrigation and their effectiveness in calcium hydroxide removal ................ 4 1.3.1 Syringe needle irrigation ......................................................................................... 5 1.3.2 Sonic irrigation ........................................................................................................ 7 1.3.3 Ultrasonic irrigation ................................................................................................ 9 viii 1.3.4 Multisonic irrigation ............................................................................................. 10 1.3.5 Effectiveness of calcium hydroxide removal by different irrigation methods ..... 12 1.4 Study model .................................................................................................................. 13 1.4.1 Existing models in the literature ........................................................................... 14 1.4.2 3D printing in endodontics .................................................................................... 14 Chapter 2: Aims and hypotheses ................................................................................................16 2.1 Rationale ....................................................................................................................... 16 2.2 Research question ......................................................................................................... 16 2.3 Specific aims ................................................................................................................. 17 2.4 Study hypotheses (H) .................................................................................................... 18 2.5 Null hypotheses (Ho) .................................................................................................... 19 Chapter 3: Materials and methods .............................................................................................20 3.1 Experimental design ...................................................................................................... 20 3.2 3D printed transparent root canal model ....................................................................... 20 3.3 Pre-experiment model assessment and preparation ...................................................... 22 3.4 Calcium hydroxide placement ...................................................................................... 25 3.5 Experimental groups ..................................................................................................... 25 3.6 Running the experiments and assessment of calcium hydroxide removal ................... 31 3.7 Statistical data analysis ................................................................................................. 32 3.7.1 Chi-square test ...................................................................................................... 32 3.7.2 Binary logistic regression analysis ........................................................................ 32 3.7.3 Independent t-test .................................................................................................. 33 Chapter 4: Results ........................................................................................................................34 ix 4.1 Visual assessment of outcome ...................................................................................... 34 4.2 Effects of different variables on efficiency of calcium hydroxide removal from root canals with and without internal resorptions – Bivariate analysis ............................................ 40 4.2.1 Differences based on presence of resorptions ....................................................... 41 4.2.2 Differences between GW and other irrigation systems in cleaning shallow resorptions ............................................................................................................................. 41 4.2.3 Differences between GW and other irrigation systems in cleaning deep resorptions ............................................................................................................................. 42 4.2.4 Differences based on composition of calcium hydroxide ..................................... 43 4.2.5 Differences based on the location of resorption ................................................... 44 4.3 Effects of different variables on efficiency of calcium hydroxide removal from root canals with and without internal resorptions – Multivariate analysis ....................................... 44 4.4 Effect of irrigation device on the calcium hydroxide removal time ............................. 45 Chapter 5: Discussion ..................................................................................................................47 5.1 Significance of the study ............................................................................................... 47 5.2 Major findings ............................................................................................................... 48 5.3 Limitations .................................................................................................................... 57 5.4 Future directions ........................................................................................................... 58 Chapter 6: Conclusion .................................................................................................................60 Bibliography .................................................................................................................................61 x List of Tables Table 3-1. Main parameters of the 3D printed transparent root canal model with internal resorptions. .................................................................................................................................... 22 Table 4-1. Comparison of the effects of the presence of resorptions on calcium hydroxide removal by all irrigation systems. ................................................................................................. 41 Table 4-2. Comparison of using GW vs other methods of irrigation for calcium hydroxide removal from shallow resorptions. ............................................................................................... 42 Table 4-3. Comparison of using GW vs other methods of irrigation methods for calcium hydroxide removal from deep resorptions. ................................................................................... 43 Table 4-4. Comparison of the effects of the composition of calcium hydroxide on its removal from root canals and resorptions. .................................................................................................. 43 Table 4-5. Comparison of the effects of location of the resorption on calcium hydroxide removal........................................................................................................................................................ 44 Table 4-6. Binary logistic regression model of predictors of calcium hydroxide removal. ......... 45 xi List of Figures Figure 3-1. A 3D design of root canal model with internal resorptions in AutoCAD software. Anterior left canal (red arrow), anterior right canal (green arrow), posterior canal (yellow arrow)........................................................................................................................................................ 21 Figure 3-2. 3D printed model with Clear Tape on the front surface. ............................................ 22 Figure 3-3. Coronal view of the 3D model with abbreviations for anterior left (AL), anterior right (AR) and posterior (P) canals. ...................................................................................................... 23 Figure 3-4. 169L FG Surgical carbide tapered fissure bur. .......................................................... 24 Figure 3-5. 3D printed model with enlarged side vents from AR and AL internal resorptions. .. 24 Figure 3-6. ONI irrigation set up. ................................................................................................. 27 Figure 3-7. DNI irrigation set up. ................................................................................................. 28 Figure 3-8. EA irrigation set up. ................................................................................................... 28 Figure 3-9. PF irrigation set up. .................................................................................................... 29 Figure 3-10. Coronal view of the SoundSeal reline of the access and sealed AR and AL orifices prior to running tests on P canal. .................................................................................................. 30 Figure 4-1. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by ONI 5 ml/min irrigation in shallow resorptions of AR canal. Upper images: before irrigation, lower images: after irrigation. ....................................................................................................... 34 Figure 4-2. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by ONI 15 ml/min irrigation in shallow resorptions of AR canal. ............................................... 34 Figure 4-3. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by DNI 5 ml/min irrigation in shallow resorptions of AR canal. ................................................. 35 xii Figure 4-4. Representative images of before and after Multi-Cal (a) and UltraCal XS(b) removal by EA irrigation in shallow resorptions of AR canal. ................................................................... 35 Figure 4-5. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by PF 15 ml/min irrigation in shallow resorptions of AR canal. .................................................. 36 Figure 4-6. Representative images of before and after Multi-Cal (a) and UltraCal XS(b) removal by GW irrigation in shallow resorptions of AR canal. ................................................................. 36 Figure 4-7. Representative images of before and after Multi-Cal (a) and UltraCal XS(b) removal by ONI 5 ml/min irrigation in deep resorptions of AL canal. ...................................................... 37 Figure 4-8. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by ONI 15 ml/min irrigation in deep resorptions of AL canal. .................................................... 37 Figure 4-9. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by DNI 5 ml/min irrigation in deep resorptions of AL canal. ...................................................... 38 Figure 4-10. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by EA irrigation in deep resorptions of AL canal. .......................................................... 38 Figure 4-11. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by PF 15 ml/min irrigation in deep resorptions of AL canal. ......................................... 39 Figure 4-12. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by GW irrigation in deep resorptions of AL canal. ........................................................ 39 Figure 4-13. Percent of total GW irrigation time by resorption type and composition of calcium hydroxide. ..................................................................................................................................... 46 xiii List of Abbreviations 3D Three dimensional % Percentage Ca(OH)2 Calcium hydroxide CFD Computational fluid dynamics CI Confidence interval cpm Cycles per minute DNI Double-side-vented needle irrigation DOM Dental operating microscope DW Distilled water EA EndoActivator EDTA Ethylenediaminetetraacetic acid GW GentleWaveTM system H Study hypothesis Ho Null hypothesis IRR Internal root resorption kHz Kilohertz min(s) Minute(s) ml Milliliter mm Millimeter n Number of tests NaOCl Sodium hypochlorite xiv OR Odds ratio ONI Open-ended needle irrigation p Significance PF PiezoFlow PUI Passive ultrasonic irrigation s Second SEM Scanning electron microscope SNI Syringe needle irrigation SPSS Statistical Package for the Social Sciences STL Standard Triangle Language WL Working length xv Acknowledgements Having Dr. Haapasalo as my research supervisor has been an absolute privilege. Without his guidance on turning initial concept of the resorption model into reality, continuous feedback throughout the research development and extensive knowledge in the area of irrigation and endodontic disease, this project could never have happened. I would also like to extend a special thank you to my committee members, Dr. Shen and Dr. Hieawy. From helping obtain the models and necessary elements of this research early on to always willing to answer my endless questions, Dr. Shen was a paramount part of this research. I am forever grateful for her positivity and words of encouragement. Dr. Hieawy’s support in troubleshooting experimental challenges of 3D printing is what allowed this project take off the ground. The students of both UBC Graduate and Undergraduate Endodontic programs are truly blessed to have such a selfless and passionate educator. Interpretation of this project’s data would not have been possible without Dr. Aleksejuniene. Owing to her lectures and challenging home tasks, as well as the hours she dedicated to review my results, I was able to finally scratch the surface of understanding statistics. This allowed correct set up of variables and experimental tests from the start and made the data analysis surprisingly enjoyable. My eternal gratitude goes to Dr. Coil for giving me a chance to learn from this extraordinary group of people, for teaching me how be critical of scientific research and for always making me xvi think outside the box. Being welcomed to the UBC GradEndo family I was exposed to the best mentors, co-residents and support staff I could possibly ask for. Finally, this journey would never have been the same without the love and encouragement by my partner Joe. Thank you for your patience, kindness and never letting doubt halt my pursuit of excellence in this field. xvii Dedication To my parents, Elena and Georgy, for always pushing me to explore life outside the comfort zone and to embrace every opportunity to learn. Thank you for teaching the value of perseverance, personal integrity, passionate enthusiasm and lifelong curiosity. Without your unconditional love and support I would not dream to stand where I do. 1 Chapter 1: Review of the literature 1.1 Internal inflammatory root resorption Internal inflammatory root resorption (IRR) is a progressive destructive loss of dental hard tissue caused by odontoclastic multinuclear cells, stimulated by inflammation of the pulp tissue (1,2). As the mineral structure is destroyed, the remaining spaces get filled in by granulation tissue or a mixture of granulation tissue with bone-like or cementum-like material (3). 1.1.1 Etiology and pathogenesis Initiation of IRR requires damage to the protective pre-dentin and odontoblast cell layer with subsequent exposure of inner mineralized tissues to the clastic cells (4,5). However, exposure of the mineralized tissue alone results in transient change only and is self-limiting in nature. In order for IRR to progress, continuous stimulus such as presence of bacteria or mechanical irritation is needed (4,6). While the exact etiology of pre-dentin and odontoblast destruction is unclear, some of the suggested causes include trauma, chronic pulpitis, infection, cracked tooth and orthodontic treatment (7–9). Advancement of IRR requires the pulp tissue apical to the site of resorption to be vital and the pulp tissue coronal to the site of resorption to be partially or completely necrotic (4). This way the vital tissue maintains blood and nutrient supply to the clastic cells, while necrotic tissue stimulates clastic activity. Once the entire root canal system is necrotic, the internal inflammatory root resorption self-arrests (2). 2 1.1.2 Presentation and clinical findings Majority of the time, teeth with IRR do not have any symptoms. While some vital tissue remains inside the root canal system, patients may develop pulpitis. In cases of coronal IRR, pinkish discoloration of the crown may be evident on clinical examination (2). Asymptomatic IRR can advance to a significant size and potentially perforate the tooth (2,10). Radiographically, IRR presents as round, oval or irregular shaped radiolucent enlargement in the pulp chamber or root canal (1,2). In the early stages, resorption is frequently missed by the conventional radiography and even CBCT as the depth of the lesion needs to be at least 0.1 mm in order to be detected (10,11). Traditionally, IRR has been thought to be a very rare entity with unknown prevalence (1,2). However, a clinical and scanning electron microscope (SEM) study by Gabor et al. (10) of extracted teeth with confirmed clinical diagnosis showed that IRR is a frequent occurrence in teeth with pulpitis and necrosis, with 50% and 77% prevalence respectively. 1.1.3 Treatment challenges Overall, if detected and treated early and pending the tooth with IRR is restorable, root canal treatment is the treatment of choice, and the tooth can have a favorable long-term prognosis (1,2). The goal of root canal therapy in treatment of teeth with IRR is to remove all pulpal tissue which is sustaining the resorptive process, to disinfect and obturate the tooth (1). However, the complex anatomy and irregularity of the lesions cause challenges in the chemomechanical root canal preparation as neither the instruments, nor the irrigants can contact all the walls (12–14). 3 Therefore, irrigant activation and use of calcium hydroxide intracanal medication are considered indispensable in the treatment of IRR (1,15). 1.2 Calcium hydroxide Calcium hydroxide (Ca(OH)2) is a widely used interappointment intracanal endodontic medicament (16). It exists as a white odorless powder with a highly basic pH (12.5-12.8) and low water solubility (17,18). All of it biological actions stem from the dissociation reaction into Ca2+ and OH- ions (17). Ca(OH)2 can exist in three main types of vehicles: water soluble, viscous and oil-based (18) and those vehicles determine its physical and chemical properties and consequently its clinical uses (17). The type of vehicle also influences the ease of Ca(OH)2 removal with oil-based Ca(OH)2 formulations displaying greater difficulty of removal compared to water based ones (19). Barium sulfate is added to calcium hydroxide mixtures in order to improve the radiopacity. It remains controversial whether its addition has an effect on Ca(OH)2 removal (20,21). 1.2.1 Benefits of using calcium hydroxide in IRR As an intracanal medicament, calcium hydroxide has a number of important functions. It is able to successfully eliminate most bacteria persistent after chemomechanical preparation in an endodontic infection (22,23). This is due to the release of highly potent hydroxyl ions from calcium hydroxide in an aqueous environment (24). Hydroxyl ions can disrupt bacterial cytoplasmic membranes, denature proteins and split DNA strands (18,24). 4 When treatment of IRR is considered, calcium hydroxide has further advantages: ability to necrotize remaining pulp tissue in the resorption lacunae and control of the bleeding (2,18). The highly alkaline environment created by calcium hydroxide promotes hard tissue formation through activation of alkaline phosphatase and neutralization of lactic acid released from osteoclasts (18). Collectively, these measures inhibit progression of IRR and help with effective disinfection of the root canal system. 1.2.2 Consequences of incomplete calcium hydroxide removal Despite its many beneficial actions, failure to completely remove calcium hydroxide prior to obturation can have unfavorable consequences (15,25). Presence of residual calcium hydroxide can negatively affect the sealing ability of numerous sealers: RealSeal (SybronEndo, Sybron Dental Specialties, Orange, CA, USA) and Endofill (Dentsply, Rio de Janeiro, Brazil) (26), Tubli-sealTM sealer (Kerr, Romulus, MI, USA) (27), Epiphany sealer (Pentron, Wallingford, CT, USA) (28) and Total Fill BC sealer (FKG Dentaire, Crêt-du-Locle, Switzerland) (29); can prevent adequate penetration of sealers into dentinal tubules (30), can diminish the push-out bond strength of AH-26 (Dentsply, DeTrey, Germany) and BC sealer (Brasseler, Savannah, USA) (31) and influence the setting reaction of zinc oxide-eugenol sealer causing it to become brittle and granular (32). 1.3 Methods of irrigation and their effectiveness in calcium hydroxide removal Most commonly, removal of intracanal calcium hydroxide was achieved through instrumentation with master apical file followed by copious sodium hypochlorite (NaOCl) and/or 5 ethylenediaminetetraacetic acid (EDTA) irrigation (16). However, canal irregularities such as IRR, isthmi, lateral anastomoses, C-shaped anatomy and apical deltas all pose a challenge to complete calcium hydroxide removal by conventional irrigation methods (33,34). As a result, several different irrigation methods have been developed to improve the effectiveness of intracanal calcium hydroxide removal and their mechanism of action is discussed below. 1.3.1 Syringe needle irrigation Irrigation has been traditionally performed using plastic syringes of varying sizes (1-20 ml) with attached irrigation needles, most commonly, of sizes 27 gauge, 30 gauge and 31 gauge (35). As the pressure is applied to the syringe barrel, irrigant gets extruded into the root canal system. The needle is kept stationary at a pre-defined depth within the canal or is moved in an up-and-down motion (36). A number of factors play a role in the efficacy of syringe needle irrigation (SNI) and they include proximity of the needle to the apex, the size of the needle (37–39), curvature and shape of the root canal (40), needle design (41–43), size of the preparation (44), amplitude of the needle motion (45), flow rates (46) and volume of the irrigant (47). Multiple authors have demonstrated that in order for SNI to be effective, the irrigation needle needs to be placed as close to the intra-canal material as possible (37–39,43) and this is better 6 achieved by smaller gauge needles, compared to larger gauge needles (37,38). However, the more apical placement of the needle increases the chance of apical extrusion of the irrigant (38). The design of the needle is also significant. Irrigation needle designs include open-ended needles with flat, beveled or notched tips and closed-ended needles with side-vented, double-side-vented or multi-vented configuration (41). Chen et al. (42) have demonstrated that open-ended needles produced greater apical turbulence intensity as well as higher maximum fluid velocity speed than side-vented needle. These findings were supported by Shen et al. (43), who found the highest apical pressure with open-ended beveled needle and the lowest with closed-ended side-vented needle. Furthermore, the open-ended and closed-ended needles tend to create differences in fluid movement upon ejection. Using Computational Fluid Dynamics (CFD), Boutsioukis et al. (41) showed that open-ended needles produced a jet in apical direction while the closed-ended needles developed multiple vortices. Due to this variation in apical irrigant flow, open-ended needles had a significantly more effective irrigant replacement than their closed-ended counterparts. This advantage, however, also came with the consequence of greater apical pressure. An increase in apical pressure appears to be a consequence of not only depth of needle placement (38) and needle design (41,42) but also high irrigation flow rates (46) and lack of or small amplitude of needle movement within the canal (45). The authors advise to keep these patient 7 safety considerations in mind when choosing the needle design and method of irrigant delivery (46). Despite its ubiquity, SNI remains limited in its ability to irrigate complex root canal anatomy. Its action beyond the tip of the needle is finite, the overall mechanical flushing action is quite weak (35,36) and apical penetration of the irrigant can be prevented by formation of air bubbles, a phenomenon also known as vapor lock (48). Consequently, several devices utilizing sonic, ultrasonic and multisonic energy have been developed to enhance the efficacy of irrigation (35). 1.3.2 Sonic irrigation The use of sonic instrument for endodontic irrigation was first reported on by Tronstad et al. (49) with the goal of improving the ease and speed of chemomechanical debridement. Unlike the ultrasonic irrigation, sonic irrigation works at a lower frequency of 1-6 kHz and creates lower shear stresses (50). Sonic irrigation is also dissimilar to ultrasonic in its oscillation pattern. A minimal oscillation of amplitude (known as a node) is located at the attachment level of the sonic handpiece and the tip and the maximum oscillation of amplitude (known as the antinode) is located at the tip. If the movement of the sonic tip is restricted within the canal, the tip moves in purely longitudinal fashion, resulting in large amplitude of motion and high debridement efficacy (51). Multiple sonic irrigation devices exist on the market and one of the most commonly used devices is EndoActivator (EA; Dentsply Sirona Endodontics, Tulsa, OK, USA). EA consists of two parts: a portable battery-operated three-prong handpiece and disposable smooth non-cutting 8 polymer tips of three sizes (15/02, 25/04, 35/04 taper) (36). After the cleaning and shaping of the canal is completed, the irrigant is introduced into the canal space using an endodontic syringe. Appropriate tip is then snapped on the EA handpiece, introduced into the canal and sonically activated (up to 10,000 cpm) (52). According to the manufacturer, this hydrodynamic activation allows the irrigant to penetrate hard to reach areas of the root canal system (53). Multiple authors have investigated the effectiveness of EA irrigation in comparison with other irrigation methods. EA was shown to be significantly better at smear layer removal in the apical third of curved canals than 27 gauge syringe needle irrigation (with and without manual gutta-percha agitation) or RinsEndo (Dürr Dental GmbH & Co KG, Bietligheim-Bissengen, Germany) by Caron et al. (54). EA also demonstrated comparable irrigation efficacy to ultrasonic irrigation in simulated lateral canals at 4.5 and 2 mm depth coronally from the working length (55). When EA and E7 ultrasonic tip of Varios LUX (Nakanishi Inc, Kanuma, Japan) were used to mechanically agitate chlorhexidine 5 mm above a bacterial biofilm on collagen-coated hydroxyapatite discs, EA displayed the highest levels of bactericidal activity at both 1- and 3- minute exposure times (53). Not all studies were in agreement with such favorable outcomes for EA. Townsend and Maki (56) compared EndoVac irrigation (Smart Endodontics; Discus Dental, Culver City, CA), EA, F-File (Plastic Endo, Lincolnshire, IL), 29 gauge SNI, MiniEndo II ultrasonic unit (Spartan EIE Inc, San Diego, CA) and Micromega 1500 sonic handpiece (Medidenta Int Co, Woodside, NY) in their efficacy of bacterial removal from plastic simulated canal. Their study found no significant difference between F-File, EA, Micromega 1500 sonic handpiece and ultrasonic 9 irrigation. Uroz-Torres et al. (57) evaluated effectiveness of EA in smear layer removal in coronal, middle and apical thirds of a single-canal teeth with and without final rinse of 17% EDTA. The authors concluded that EA did not provide advantage in smear layer removal compared to SNI. 1.3.3 Ultrasonic irrigation First brought to the field of endodontics by Richman in 1957 (58), ultrasonic devices can be divided into those with concurrent ultrasonic irrigation and instrumentation (UI) and those activated after instrumentation has been completed - passive ultrasonic irrigation (PUI) (36). The term passive refers to the function of purely activating the file without cutting or touching the dentin walls (59). PUI transmits acoustic energy from oscillating file/wire to the irrigant by utilizing ultrasonic waves. This action can then create acoustic streaming and transient cavitation of the irrigant (60). Acoustic streaming, known as development of steady rapid vorticial flow close to a small vibrating object (60), can produce shear stresses and improve chemomechanical debridement of the root canal system (61). The speed of acoustic streaming is dependent on the size of the file and the power setting of the ultrasonic unit with most ideal outcome expected at higher power setting and with small file freely oscillating in the canal (60,62). Cavitation is the process of small bubbles growing and collapsing within the fluid (50). This violent action generates shock waves, turbulence and elevates the temperature of the solution (61,63). 10 PUI can be used with two methods of irrigant delivery: intermittent flush and continuous flush. The former works by injecting the irrigant into the root canal, ultrasonically activating the file/wire and then replenishing the irrigant several times after each cycle (64). In the latter, the irrigant is continuously delivered through the port on the ultrasonic file as the file is activated in the canal. Thus, irrigant replenishment is not needed after each activation cycle (59). Irrisafe ultrasonic tip (Satelec Acteon, Merignac, France) and ProUltra PiezoFlow (PF; Dentsply Sirona Endodontics) are examples of intermittent flush and continuous flush ultrasonic systems respectively. Ultrasonic devices produce higher oscillation frequency (25-42 kHz) compared to sonic activators (59) and unlike sonic devices, ultrasonics have multiple nodes and antinodes along the length of the wire/file creating a transverse vibration (64). Studies on ultrasonic irrigation have shown that PUI produced significantly greater dentin debris and pulp tissue removal when compared to SNI (65–67). When examined against sonic activation, PUI was shown to be significantly more effective in removal of dentin debris from simulated grooves (89% and 5.5-6.7% dentin debris free grooves for PUI and sonic groups accordingly) (68). Additionally, PUI also appears to have a synergistic effect with NaOCl resulting in greater organic tissue dissolution (69). 1.3.4 Multisonic irrigation GentleWaveTM (GW; Sonendo Inc, Laguna Hills, CA) is a novel multisonic endodontic cleaning system, which consists of a console and a handpiece. During treatment, the tip of the molar 11 handpiece is held inside the endodontic access 1 mm above the pulp chamber floor as the degassed solution is ejected from the console at a speed of 45 ml/min and a temperature of roughly 40 °C. A closed system is ensured by building a platform with SoundSeal material (Sonendo Inc) between the head of the handpiece and occlusal surface of the treated tooth. The handpiece acts to simultaneously collect the excess irrigant from the pulp chamber through an in-built 5-point vented suction system (70). GW generates a broad range of multisonic waves within the irrigation fluid. The acoustic energy created by formation and collapse of thousands of microbubbles travels throughout entire root canal system (71). When the solution enters the orifices of the canals, gentle vortical flow and slight negative pressure are produced inside (72). GW has proven to be a highly efficient irrigation system by numerous authors. In a study by Haapasalo et al. (70) GW was shown to dissolve bovine muscle tissue 8 times faster than Piezon Master 700 ultrasonic system (EMS, Dallas, TX) in a simulated model. It was also able to achieve higher biofilm reduction compared to PUI (71,73) and greater residual debris removal compared to SNI (71) and continuous flush ultrasonic irrigation (74) in extracted human molar teeth. Its safety was confirmed in vitro by Charara (75) who showed no apical extrusion by GW and EndoVac, as opposed to 33% incidence of apical extrusion with SNI. Haapasalo et al. (72) supported these findings and found GW maintained negative pressure irrespective of the size of 12 canal instrumentation. When used in clinical practice, cases treated with GW showed high success rates of 97.7% at 12-month re-evaluation (76). 1.3.5 Effectiveness of calcium hydroxide removal by different irrigation methods Ability to completely remove calcium hydroxide from the root canal system remains a challenge for most endodontic irrigation techniques and many studies on the subject have been published (34). A study by Al-Garni et al. (77) examined the efficacy of calcium hydroxide removal with EA and SNI in single-rooted teeth. They found that while both irrigation methods were able to completely remove Ca(OH)2 in the coronal third of the canal, minimal Ca(OH)2 removal was achieved for either group in the middle or apical thirds. Kenee et al. (78) similarly demonstrated failure of SNI, rotary instrumentation and ultrasonic devices to remove Ca(OH)2 in its entirety from the mesial canals of mandibular molars. Multiple authors also investigated efficacy of Ca(OH)2 removal in more complex root canal anatomy. In lower molar C-shaped configuration, attempts to remove Ca(OH)2 by SNI, EA and ultrasonic activation resulted in 68%, 28% and 31% remaining Ca(OH)2 correspondingly (34). When simulated internal resorption cavities were created by Topcoglu et al. (15), none of the tested irrigation systems (PUI, SNI, canal brush, EA and a self-adjusting file (SAF; Re-Dent-Nova, Ra’nana, Israel)) could completely remove Ca(OH)2. Both Van der Sluis et al. (33,79)and Capar et al. (79) attempted to mimic more complicated root canal anatomy with artificial grooves 13 in the apical part of the root. PUI demonstrated the greatest ability to remove Ca(OH)2 from the grooves in both studies, albeit not completely. The most promising Ca(OH)2 removal results thus far have been shown by GW. A micro-CT study by Ma et al. (25) compared GW, PUI and SNI in their ability to remove Ca(OH)2 from mesial and distal canals of extracted mandibular molars. GW was found to remove 100% of Ca(OH)2, while PUI removed 61.66% +/- 25.54%. and SNI removed 47.82+/- 16.36% of Ca(OH)2. A more recent study by Liu et al. (21) examined Ca(OH)2 removal from simulated isthmi in 3D printed molar model by SNI of varying designs and flow rates, intermittent flush and continuous flush ultrasonic systems and GW. GW and continuous flush ultrasonic system were the only techniques able to remove Ca(OH)2 from the isthmi completely, with GW taking an average 2-3 x less time than its counterpart. 1.4 Study model Over the years, numerous in vitro endodontic studies have been performed on extracted teeth. The main advantages of using natural teeth include realistic complexity of tooth anatomy and near-true physical properties of materials, such as dentine, encountered in clinical practice. However, extracted teeth come with many drawbacks. Lack of tooth structure transparency prevents the investigators from visualizing the processes within the tooth without destructive processes. Furthermore, studies requiring large sample size struggle to match teeth for test situations accurately due to lack of standardized anatomy. Lastly, ethical considerations and concerns over cross infection also exist (80,81). 14 1.4.1 Existing models in the literature Several models have been developed in attempts to compare Ca(OH)2 removal efficacy by different irrigation methods in challenging clinical situations. These include use of a standardized groove in the apical 1/3 of the tooth (79), creating a simulated IRR cavity with a spherical bur (20,82,83) or with a spherical bur and 20% nitric acid (82). Those models lack irregularities of complicated root canal anatomy, allow visualization of the outcome at a specified end point only and require the teeth to be split longitudinally, making the process destructive (21). 1.4.2 3D printing in endodontics 3D printing is an additive process, where material is incrementally deposited in layers (84). Many 3D applications exist in the field of endodontics: guided surgical and non-surgical endodontics, pre-clinical training, dental pulp regeneration (81,85,86). 3D printed technology allows manufacturing of standardized tooth models with complexities such as dens invaginatus, internal and external root resorption, pulp stones and isthmi (21,85). A number of 3D printed technologies are used in endodontics with ColorJet printing (CJP), MultiJet printing (MJP) and PolyJet printing being most common (80,81). MultiJet and PolyJet printing are achieved by spraying light sensitive polymer in very thin layers and curing each layer on an incrementally descending platform (84,85). This process results in high resolution (approximately 16 microns), giving the objects great accuracy, fine detail and high-quality finish (81,85). 3D technology does come with some disadvantages, such as high cost, occurrence of a 15 staircase effect from layer deposition, difficulty in removal of support material post processing and absence of ethical and legal ramifications (85). 16 Chapter 2: Aims and hypotheses 2.1 Rationale Calcium hydroxide is often used in the treatment of IRR. In addition to disinfection of the root canal system, it necrotizes resorptive tissue, controls the bleeding and promotes hard tissue formation (2,18). However, failure to remove it prior to obturation has the potential to negatively influence the sealing ability of many sealers (26,27,30). Multiple authors have examined the effect of various irrigation techniques on calcium hydroxide removal from simulated internal resorption cavities in extracted teeth (15,82,83). To the best of our knowledge, none of the studies thus far have used 3D printed models to assess the efficacy of different irrigation methods on calcium hydroxide removal from IRR. 2.2 Research question Do different irrigation methods differ in their effectiveness of calcium hydroxide removal in the 3D printed molar tooth model including deep and shallow internal resorptions?17 2.3 Specific aims 1. To assess whether presence of resorptions (deep or shallow) has an effect on the ability of six different irrigation systems to remove premixed calcium hydroxide from the root canal system under different testing conditions. 2. To assess whether the depth (shallow vs. deep) of resorption has an effect on the ability of the six different irrigation systems to remove premixed calcium hydroxide from the root canal system and resorptions 3. To assess if the composition of calcium hydroxide has an effect on the ability of the six different irrigation systems to remove it from the root canal system and resorptions 4. To assess if the location (coronal, middle or apical) of the resorption has an effect on the ability of the six different irrigation systems to remove premixed calcium hydroxide form the root canal system and resorptions 18 2.4 Study hypotheses (H) H1. The presence of resorptions (deep or shallow) as compared to no resorptions makes it more difficult for all irrigation methods to remove calcium hydroxide from the root canal system and resorptions. H2. GentleWave irrigation system is more effective than other irrigation methods in removing calcium hydroxide from shallow resorptions. H3. GentleWave irrigation system is more effective than other methods of irrigation in removing calcium hydroxide from deep resorptions. H4. UltraCal XS is more difficult to remove from the root canal system and resorptions than Multi-Cal with all irrigation systems. H5. The more apical the resorptions are, the more difficult it is to remove calcium hydroxide from them. H6. The type of the irrigation system, presence of resorption, location of the resorption, depth of the resorption, composition of calcium hydroxide influence the efficiency of calcium hydroxide removal from the root canal system and resorptions. 19 2.5 Null hypotheses (Ho) Ho1. The presence of resorptions (deep or shallow) as compared to no resorptions has no influence on the ability of different irrigation methods to remove calcium hydroxide from the root canal system and resorptions. Ho2. GentleWave irrigation system does not differ from other irrigation methods in effectiveness of removing calcium hydroxide from shallow resorptions. Ho3. GentleWave irrigation system does not differ from other irrigation methods in effectiveness of removing calcium hydroxide from deep resorptions. Ho4. Composition of calcium hydroxide does not impact the ability of its removal from the root canal system and resorptions by different irrigation methods. Ho5. Location of resorption has no influence on the effectiveness of calcium hydroxide removal from the root canal system by different irrigation methods. Ho6. The type of irrigation system, presence of resorptions, location of resorption, depth of resorption, composition of calcium hydroxide has no effect on the efficiency of calcium hydroxide removal from the root canal system and resorptions. 20 Chapter 3: Materials and methods 3.1 Experimental design This in vitro study was designed to assess the efficacy of calcium hydroxide removal by different irrigation methods in a simulated root canal system with and without presence of artificial internal resorptions. The parameters measured included: 1) the amount of calcium hydroxide removed from root canal system, assessed as none, partial and complete, and 2) the time required for complete calcium hydroxide removal, assessed in seconds. 3.2 3D printed transparent root canal model 3D printed root canal model of a mandibular molar tooth with a pulp chamber and three canals was designed using AutoCAD software (Version 23.1, Autodesk, Inc, CA, USA), saved in STL format. STL file was then printed on Stratasys PolyJet J5 DentaJet 5 printer (Stratasys Ltd, Eden Prairie, MN, USA) using GrabCAD Print Software (GrabCAD, Boston, MA, USA) at 0.018 mm resolution. The model was manufactured using StrataSys Biocompatible Clear MED610TM material (Stratasys Ltd) which is a transparent, rigid, biocompatible PolyJetTM material (Stratasys Ltd). This PolyJet technology allows the printed features to be detailed and precise. The mandibular tooth model was designed to have three canals: posterior (without any internal resorptions, used as control), anterior right (with shallow internal resorptions) and anterior left (with deep internal resorptions). Internal resorptions were placed in three locations within the anterior canals: in coronal, middle and apical thirds of the root canal system. All internal resorptions had side vents extending to the external surface of the model. 21 The model was developed with a circular platform at the most coronal aspect. The inner diameter of the platform was designed to match the nozzle piece of the GentleWave molar handpiece (GW; Sonendo Inc). Within the center of this platform, a hollow space was created to replicate a simulated pulp chamber. The exact model parameters are presented in Figure 3.1 and Table 3.1. Figure 3-1. A 3D design of root canal model with internal resorptions in AutoCAD software. Anterior left canal (red arrow), anterior right canal (green arrow), posterior canal (yellow arrow). 22 Resorptions Root canals Shallow Deep Anterior left Anterior right Posterior Maximum height (mm) 2.83 3.00 N/A N/A N/A Maximum width (mm) 2.40 4.09 N/A N/A N/A Maximum depth (mm) 0.94 1.70 N/A N/A N/A Root canal length (mm) N/A N/A 16.00 16.00 16.00 Root canal size N/A N/A 30/.4 30/.4 30/.4 Table 3-1. Main parameters of the 3D printed transparent root canal model with internal resorptions. 3.3 Pre-experiment model assessment and preparation The 3D printed model was examined under a dental operating microscope (DOM; Zumax Medical Co., LTD, Suzhou, China) at 4.2x, 6.9x and 10.4x magnifications to assess the transparency of the material and to check for presence of any imperfections and/or cracks. A piece of Clear Tape (Scotch TM, 3M, Saint Paul, MN, USA) was placed on the front surface of the model to improve the clarity of the material and to reduce potential damage from scratches throughout the experimental process (Figure 3.2). Figure 3-2. 3D printed model with Clear Tape on the front surface. 23 Canal orifices of posterior, anterior right and anterior left canals were located and labelled as P, AR and AL respectively using a Sharpie permanent marker (Newell Brands, Atlanta, GA, USA) (Figure 3.3). Patency of each canal was checked by introducing a size #10 stainless steel K-file (Dentsply Maillefer, Tulsa, OK, USA) approximately 1 mm past the apical foramen without filing. Apical foramen was defined as the point where the external surface of the model and apical extent of the canal met. Figure 3-3. Coronal view of the 3D model with abbreviations for anterior left (AL), anterior right (AR) and posterior (P) canals. AutoCAD dimensions of the canal length, pulp chamber depth and canal apical size were verified using a size 10 K file, periodontal probe with a rubber stopper and 30/04 Vortex Blue® Conform FitTM Gutta-percha cones (Dentsply Sirona Endodontics) respectively. The working length (WL) for all three canals was defined as the length from the bottom of the circular platform to the apical foramen and determined to be 22 mm. The side vents from each internal resorption in anterior right and anterior left canals were enlarged using 169L FG Surgical carbide tapered fissure bur (Brasseler) on a W&H Synea 24 Fusion WG -99 LT contra-angle handpiece 1:5 (W&H Dentalwerk Bürmoos GmbH, Bürmoos, Austria) (Figures 3.4, 3.5). None of the three canals were instrumented using rotary files or hand files at any point throughout the experiment. Only one 3D printed model was used throughout the experiments in order to standardize all tests and limit potential confounding variables. Figure 3-4. 169L FG Surgical carbide tapered fissure bur. Figure 3-5. 3D printed model with enlarged side vents from AR and AL internal resorptions. 25 3.4 Calcium hydroxide placement Two formulations of calcium hydroxide were used: Multi-CalTM (Puldent Corporation, Watertown, MA, USA) and UltraCalTM XS (Ultradent Products Inc, South Jordan, UT, USA). According to the manufacturers Multi-Cal is 39% calcium hydroxide suspended in aqueous hydroxyethylcellulose base with barium sulfate and UltraCal XS is <35% calcium hydroxide, <20% barium sulfate, aqueous matrix. The calcium hydroxide formulations were introduced into the canals using 21 mm long 29 gauge NaviTipTM (Ultradent Products Inc). In canals with internal resorptions calcium hydroxide was introduced at the level of the resorption until that resorption was completely filled, as confirmed by some backflow into the side vents. The NaviTip needle was then withdrawn coronally to fill the middle and coronal resorptions in the similar manner until the material was extruded from the orifice. Complete filling of the root canals and internal resorptions was confirmed under a DOM. Each set of experiments was performed on one canal at a time. Untested canals were sealed using SoundSeal material (Sonendo Inc) at the canal orifices. Tested canals were sealed using SoundSeal at the apical foramen and side vents (if applicable) after placement of calcium hydroxide material. Throughout the experiment, the model was held in a sample holder (Tornim, Torno Academico, Industria Brasileira, Brazil) at a 60 degree angle as measured by Angle Meter 360 (App Store, Apple Inc TM, Cupertino, CA, USA). 3.5 Experimental groups Calcium hydroxide was removed from the root canal system using the following six methods: 25 mm 30 gauge NaviTip open-ended irrigation needle (ONI) at rates of 5 ml/min and 15 ml/min, 26 27 mm long 31 gauge NaviTip double-side-vented needle (DNI) at a rate of 5 ml/min, 25/04 EndoActivator tip (EA; Dentsply Sirona Endodontics), ProUltra PiezoFlow ultrasonic 25 gauge irrigation needle (PF; Dentsply Sirona Endodontics) at a rate of 15 ml/min and the GentleWave System. Irrigation in all experimental groups was done until maximum irrigation times (2 minutes for ONI and DNI, 1 minute for EA and PF and 6 minutes 15 seconds for GW using distilled water (DW) at room temperature). Six experimental irrigation groups were set up and each group was further divided into six subgroups (n=10 each) according to two formulations of calcium hydroxide (Multi-Cal or UltraCal XS) and type of resorption present (none/shallow/deep). A total of 360 experiments were performed and recorded using Sony Alpha 7R II digital camera (Sony, Bangkok, Thailand). Group 1 – ONI 5 ml/min 25 mm length 30 gauge NaviTip open-ended irrigation needle was attached by a Luer-lock connection to Tygon Standard Tubing of 4.8 mm outer diameter and 1.6 mm wall thickness (Ismatec, Wetheim, Germany). A digitally controlled peristaltic pump (IPC High Precision Multichannel Dispenser, Ismatec) was used to deliver the distilled water at a precise flow rate of 5 ml/min. The pump was pre-set to stop the delivery of the distilled water at a maximum time of two minutes. The peristaltic pump and needle flow rates were calibrated at the start of each day or any time the needle was changed and/or the flow rate was adjusted. 27 The irrigation needle was placed inside the test canal 1 mm short of the WL (Figure 3.6). The needle was then moved in a 2-3 mm up-and-down motion. Overflow of water was suctioned from occlusal access using a 0.019 inch UltraDentTM capillary tip (Ultradent Products Inc) attached to a portable suction pump (Vacu-Aide QSU Quiet Suction Unit, Devilbliss Healthcare, Mannheim, Germany). Figure 3-6. ONI irrigation set up. Group 2 – ONI 15 ml/min Same irrigation needle and methods as Group 1 except the flow rate was changed to 15 ml/min. Group 3 – DNI 5 ml/min Same methodology and flow rate as Group 1, except the irrigation needle was changed to 27 mm long 31 gauge NaviTip double-side-vented needle (Figure 3.7). 28 Figure 3-7. DNI irrigation set up. Group 4 – EA Test canal was filled with distilled water to the level of the canal orifice using a 31 gauge NaviTip double-side-vented needle. An EA (medium tip size 25/04) was then inserted into the canal 1 mm short of the WL and activated for 30 s at 10 000 cpm (Figure 3.8). While the EA handpiece was activated, it was moved inside the canal in short 2-3 mm vertical strokes. After 30 s the EA was removed from the canal and distilled water was replenished using the same irrigation needle while suctioning the expelled water at the orifice. EA handpiece was re-inserted into the canal and activated in the same manner as before for 20 s. The total activation time was 50 s and the replenishment time was 10 s. Figure 3-8. EA irrigation set up. 29 Group 5 – PF 15 ml/min A 24 mm long 25 gauge ProUltra PiezoFlow (PF) Ultrasonic irrigation needle (Dentsply Sirona Endodontics) was trial fitted inside the canal and stopper set at 1 mm short of binding – 15 mm length from the bottom of the circular platform (Figure 3.9). The needle was then attached to the Piezo Pilot ultrasonic handpiece (Vista Apex, Racine, WI, USA) and tightened with the ProUltra wrench. The handpiece was connected via Luer-lock to the same irrigant delivery system as Groups 1-3. Additionally, the handpiece was also attached to the Piezo Pilot ultrasonic unit (Vista Apex). The ultrasonic unit was set to power level #5 and the irrigant delivery system was set to flow rate of 15 ml/min at maximum irrigation time of 1 minute. After placement of PF irrigation needle inside the canal, irrigant delivery was started. Once the irrigant filled the canal, ultrasonic booster was activated and the needle moved 3-5 mm in an up-and-down motion taking care not to touch the root canal walls. Overflow of water was suctioned from the occlusal access as described previously. Figure 3-9. PF irrigation set up. 30 Group 6 - GW GW green nozzle (size 6) was selected as it allowed the delivery tip to be at 1 mm coronal to the pulpal floor. The nozzle piece was then attached to the GW molar handpiece. Both the nozzle piece and the procedure instrument were used for a total of 5 tests before they were discarded and replaced. SoundSeal material was used to seal the gap between the GW molar handpiece and the circular platform of the 3D printed model (Figure 3.10). The procedure instrument was primed at the start of each day and then a 60 s leakage test was performed on a different 3D model before running each test. The GW handpiece was placed into the access cavity of the circular platform and set to run irrigation protocol for a necrotic molar tooth. As per manufacturer’s recommendations, the maximum treatment time was 6 minutes and 15 seconds. This cycle was set to imitate 4 minutes cycle of 3% NaOCl, 30 s distilled water rinse, 90 s cycle of 8% EDTA and final 15 s distilled water rinse. The distilled water was delivered into the pulp chamber at a flow rate of 45 ml/min. Figure 3-10. Coronal view of the SoundSeal reline of the access and sealed AR and AL orifices prior to running tests on P canal. 31 3.6 Running the experiments and assessment of calcium hydroxide removal All experiments were performed under 4.2x magnification on Zumax DOM and were monitored on Asus external monitor (AsusTek Computer Inc., Shanghai, China) connected to the Sony Alpha 7R II digital camera. Presence of any leakage in the system was continuously assessed for all methods of irrigation. In addition to recording every experiment, pre-op and post-op pictures of each experiment were taken. Apple Stopwatch (Apple Inc. TM) was used to time all the tests. Upon completion of each experiment, the canal and resorptions were visually examined for presence of residual calcium hydroxide. The categorical outcome was defined as complete if no residual material was present, partial if some material was present and none if no material was removed. These outcomes were recorded for the canal part and resorption part of the root canal system in each test. Afterwards, the overall outcome was calculated for control and test canals as follows: control canals only contained the measurements of calcium hydroxide removal within the canal, test canals contained the worse of the outcome measurements of calcium hydroxide removal inside resorption and canal at each of the three resorption levels. For example, if at the coronal level calcium hydroxide was completely removed within the canal part but was only partially removed within the resorption, the outcome at that level was then recorded as partially removed. In cases of complete removal of calcium hydroxide prior to reaching maximum irrigation time, the numerical outcome was recorded in seconds. To account for differences between maximum removal times for the different irrigation groups, the outcome was subsequently recalculated as a complete removal percentage: 32 Complete removal percentage = (Calcium hydroxide removal time (in seconds) x 100 %) / (Maximum removal time for the specific irrigation method (in seconds)). Between each experiment, the canals and resorptions were rinsed with water and dried using Stropko irrigator attachment (Vista Apex) and 20 gauge Appli-VacTM bendable tips (Vista Apex). If residual calcium hydroxide was still present afterwards, a cycle of GW irrigation was run to clean the model. 3.7 Statistical data analysis Data was analyzed using SPSS software version 28 (SPSS Inc, Chicago, IL, USA). Bivariate analyses (Chi-square test or Fisher’s exact test) and multivariate analysis (Binary logistic regression) were performed on the categorical outcome. Bivariate analysis only (Independent t-test) was done on the numerical outcome. 3.7.1 Chi-square test Chi-square test was used to test hypotheses H1, H3, H4, H5. Fisher’s exact test was used to test hypothesis H2. For H2, H3 and H5 the outcome data was restricted to shallow resorptions and deep resorptions respectively. 3.7.2 Binary logistic regression analysis For binary logistic regression analysis, the outcome was changed into binary outcome, where None/Partial calcium hydroxide removal was coded as 1 and Complete removal was coded as 2. The variables measured included composition of calcium hydroxide (Multi-Cal = 1, UltraCal XS =2) , GW vs other types of irrigation (GW = 1, others = 2), Location of resorption (0 – no 33 resorption, 1 – coronal resorption, 2 – middle resorption, 3 – apical resorption) and Reverse resorption type (1 – deep resorption, 2 – shallow resorption, 3 – no resorption). Multicollinearity was checked prior to proceeding with binary logistic regression analysis. 3.7.3 Independent t-test Numerical outcome assessment was carried out only on cases with complete calcium hydroxide removal. Normal distribution was confirmed by calculating Z skewness and Z kurtosis as well as examining the results of Kolmogorov-Smirnov tests. Meeting normality distribution condition allowed the use of independent t-test to compare the results of calcium hydroxide removal efficacy of two independent groups (ONI 15 ml/min and GW groups). Levene’s test for equality of variances was >0.05 and indicated that the assumption for equality of variances was fulfilled. The level of statistical significance was defined as p<0.050 for all the tests. 34 Chapter 4: Results 4.1 Visual assessment of outcome The representative images of intra-resorption calcium hydroxide removal by different irrigation systems are shown in figures 4.1-4.6 for shallow resorptions and 4.7-4.12 for deep resorptions. a) b) Figure 4-1. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by ONI 5 ml/min irrigation in shallow resorptions of AR canal. Upper images: before irrigation, lower images: after irrigation. a) b) Figure 4-2. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by ONI 15 ml/min irrigation in shallow resorptions of AR canal. 35 a) b) Figure 4-3. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by DNI 5 ml/min irrigation in shallow resorptions of AR canal. a) b) Figure 4-4. Representative images of before and after Multi-Cal (a) and UltraCal XS(b) removal by EA irrigation in shallow resorptions of AR canal. 36 a) b) Figure 4-5. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by PF 15 ml/min irrigation in shallow resorptions of AR canal. a) b) Figure 4-6. Representative images of before and after Multi-Cal (a) and UltraCal XS(b) removal by GW irrigation in shallow resorptions of AR canal. 37 a) b) Figure 4-7. Representative images of before and after Multi-Cal (a) and UltraCal XS(b) removal by ONI 5 ml/min irrigation in deep resorptions of AL canal. a) b) Figure 4-8. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by ONI 15 ml/min irrigation in deep resorptions of AL canal. 38 a) b) Figure 4-9. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by DNI 5 ml/min irrigation in deep resorptions of AL canal. a) b) Figure 4-10. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by EA irrigation in deep resorptions of AL canal. 39 a) b) Figure 4-11. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by PF 15 ml/min irrigation in deep resorptions of AL canal. a) b) Figure 4-12. Representative images of before and after Multi-Cal (a) and UltraCal XS (b) removal by GW irrigation in deep resorptions of AL canal. Overall, there was a pattern to the sequence of calcium hydroxide cleaning from the resorptions by different irrigation systems. ONI and DNI usually cleaned the material stepwise from apical to coronal direction with very minimal, if any, cleaning within the resorptions for 5 ml/min flowrate. Both EA and GW cleaned the resorptions stepwise from coronal to apical direction. EA 40 was able to only partially remove calcium hydroxide from coronal resorption and displayed no cleaning capacity in middle or apical resorptions. PF cleaned the middle resorption first, followed by coronal resorption. PF did not remove calcium hydroxide from the apical resorption for any of the AR and AL cases. 4.2 Effects of different variables on efficiency of calcium hydroxide removal from root canals with and without internal resorptions – Bivariate analysis Chi-square test of independence was used to determine whether there was an association between the categorical outcome of calcium hydroxide removal and the following independent variables: presence of resorptions, irrigation system, composition of calcium hydroxide and location of resorptions. Conditions for using Chi-square test were not met for testing efficacy of GW versus other irrigation systems in calcium hydroxide removal from shallow resorptions and Fisher’s exact test was used instead. The findings of these tests are presented below. 41 4.2.1 Differences based on presence of resorptions A statistically highly significant association was found between presence of resorption and calcium hydroxide removal (p<0.001). As resorptions got deeper, the proportions of partial and complete removal outcomes reduced (Table 4.1). Resorption type Calcium hydroxide removal (%) Significance* None Partial Complete None 0.8 65.8 33.3 p <0.001 Shallow 39.7 33.1 27.2 Deep 69.2 23.6 7.2 Total 46.8 33.7 19.5 *Chi-square test Table 4-1. Comparison of the effects of the presence of resorptions on calcium hydroxide removal by all irrigation systems. 4.2.2 Differences between GW and other irrigation systems in cleaning shallow resorptions One of the counts in partial removal frequency cells was 0, therefore, one of the conditions for using Chi-square test to compare proportions between calcium hydroxide removal and irrigation method was not met. As a result, Fisher’s exact test was used instead. Compared to other types of irrigation, there was a statistically highly significant association between use of GW in removal of calcium hydroxide from shallow resorptions (p<0.001). 42 Irrigation method Calcium hydroxide removal (%) Significance* None Partial Complete Other 47.3 39.7 13.0 p <0.001 GW 1.7 0.0 98.3 Total 39.7 33.1 27.2 *Fisher’s exact test Table 4-2. Comparison of using GW vs other methods of irrigation for calcium hydroxide removal from shallow resorptions. 4.2.3 Differences between GW and other irrigation systems in cleaning deep resorptions None of the counts in the frequency tables were zero for the deep resorption group, allowing Chi-square test to be used. A statistically highly significant association was detected between use of GW in removal of calcium hydroxide from deep resorptions compared to other types of irrigation (p<0.001). Overall, deep resorptions had higher proportions of cases with no calcium hydroxide removal (77.7% and 26.7% for other types of irrigation and GW respectively) in comparison to shallow resorptions (47.3% and 1.7% for other types of irrigation and GW respectively). Additionally, while 98.3% of the shallow resorptions were completely cleaned of calcium hydroxide by GW, only 41.7% of the deep resorptions were fully cleaned by GW. 43 Irrigation method Calcium hydroxide removal (%) Significance* None Partial Complete Other 77.7 22.0 0.3 p <0.001 GW 26.7 31.7 41.7 Total 69.2 23.6 7.2 *Chi-square test Table 4-3. Comparison of using GW vs other methods of irrigation methods for calcium hydroxide removal from deep resorptions. 4.2.4 Differences based on composition of calcium hydroxide A statistically highly significant relationship was found between the composition of calcium hydroxide and its removal by irrigation devices (p<0.001). Over half of cases with UltraCal XS medicament use (58.1%) had no calcium hydroxide removal during irrigation, while Multi-Cal displayed easier removal with majority of the cases at least partially removed (42.1%). Composition of Ca(OH)2 Calcium hydroxide removal (%) Significance* None Partial Complete Multi-Cal 35.5 42.1 22.4 p <0.001 UltraCal XS 58.1 25.2 16.7 Total 46.8 33.7 19.5 *Chi-square test Table 4-4. Comparison of the effects of the composition of calcium hydroxide on its removal from root canals and resorptions. 44 4.2.5 Differences based on the location of resorption A statistically significant association between location of resorption and calcium hydroxide removal was present (p<0.050), however, it was not as high as for the other tested factors. Middle resorptions had the greatest number of calcium hydroxide removal (20.4%) when compared to coronal and apical resorptions (16.7% and 14.6% accordingly). Location of resorption Calcium hydroxide removal (%) Significance* None Partial Complete Coronal 60.4 22.9 16.7 p = 0.024 Middle 52.5 27.1 20.4 Apical 50.4 35.0 14.6 Total 54.4 28.3 17.2 *Chi-square test Table 4-5. Comparison of the effects of location of the resorption on calcium hydroxide removal. 4.3 Effects of different variables on efficiency of calcium hydroxide removal from root canals with and without internal resorptions – Multivariate analysis Omnibus test of model coefficient showed that the model was highly significant (p<0.001). The explained variation in the model ranged from 35.7% to 56.9% (for Cox & Snell R Square and Nagelkerke R square values respectively). The model correctly classified 88.1% of cases. Binary logistic regression model of predictors of calcium hydroxide removal outcome are presented in Table 4.6. 45 Variables Odds ratio 95% CI Significance Type of Ca(OH)2 2.022 1.245, 3.285 0.004 GW vs other 99.502 44.928, 202.348 <0.001 Location of resorption 1.441 1.082, 1.918 0.012 Reverse resorption type 8.774 4.998, 15.402 <0.001 Table 4-6. Binary logistic regression model of predictors of calcium hydroxide removal. When comparing effect sizes among four predictors and when the model is controlled for each of the predictors, the highest effect was for GW: Odds ratio (OR) = 99.502 (44.928, 202.348). The second-best predictor was the resorption type, where calcium hydroxide removal in the deeper resorption was more difficult than in shallow and no resorption: OR = 8.884 (1.082, 1.1918). The third best predictor was composition of calcium hydroxide with UltraCal XS being harder to remove than Multi-Cal: OR = 2.022 (1.245, 3.285). Lastly, the location of resorption also had an effect on calcium hydroxide removal, where more apical resorption was associated with greater difficulty of material removal than middle resorption, coronal resorption and intra-canal space: OR = 1.441 (1.082, 1.918). All four predictors were highly significant (p<0.050). 4.4 Effect of irrigation device on the calcium hydroxide removal time ONI 15 ml/min and GW were the only irrigation methods able to completely remove calcium hydroxide from the root canal system (control and test canals). The mean complete removal percentage was 33.371 +/- 11.395% for ONI 15 ml/min and 48.507 +/- 16.164% for GW. 46 The independent t-test showed that GW was significantly more effective in removing calcium hydroxide from canals with and without resorptions by an average of 15.137% compared to ONI 15 ml/min. When the data was restricted to canals with resorptions, GW was the only irrigation device able to remove the calcium hydroxide completely, however, not in all cases. As seen in Figure 4-13 GW was unable to remove calcium hydroxide completely in any of the cases with deep resorptions. Furthermore, presence of resorption and using UltraCal XS were found to increase calcium hydroxide removal time. UltraCal XS displayed greater variation in outcome values compared to Multi-Cal for both control canal and canal with shallow resorptions. Figure 4-13. Percent of total GW irrigation time by resorption type and composition of calcium hydroxide. 47 Chapter 5: Discussion 5.1 Significance of the study The use of calcium hydroxide is indispensable in the treatment of internal inflammatory root resorption. In addition to its antibacterial activity, it limits the bleeding of remaining pulp tissue and also necrotizes it, making necrotic tissue more soluble to sodium hypochlorite (2). Its ability to induce hard tissue formation can provide a successful outcome even in cases where the resorptive defect perforates the tooth structure (87). However, similarly to other internal root canal intricacies such as isthmi, lateral canals, C-shaped anatomy and apical deltas (33,34) IRR is a challenge when it comes to the ability of various irrigation techniques to remove calcium hydroxide completely. Many authors have studied the effects of syringe needle irrigation, ultrasonic irrigation, sonic irrigation, novel off-center file technology and negative pressure irrigation on the efficacy of Ca(OH)2 removal from simulated internal resorption cavities in extracted teeth (15,20,82). The overwhelming majority of the irrigation methods were unable to fully remove calcium hydroxide from IRR cavities in these studies. To the best of our knowledge, this is the first study to evaluate the efficacy of calcium hydroxide removal in a 3D printed model with simulated internal resorption cavities. 3D printed model was chosen for a number of reasons. Firstly, it allowed a dynamic assessment of irrigant flow rather than drawing conclusions on irrigant efficacy at a specified end point (21). Secondly, the test outcome could be visually examined and documented without splitting the 48 model or taking radiographic imaging. Lastly, it provided a standardized and reproducible environment for the experiments (80). However, the model did have multiple drawbacks. It had straight round canals which is not reflective of a real clinical situation. Furthermore, multiple resorptions were present in each canal for the purpose of assessing effect of resorption location on calcium hydroxide removal. This is also not representative of a typical IRR scenario in vivo. Other aspects of the model could have interfered with the outcome of the present study. They include the dissimilarity between polymer physical properties and those of dentine (80) as well as difference in behavior of bone and PDL compared to SoundSeal resin (21). These negative aspects of the model design need to be considered when analyzing the study results. They could also be used for future modifications and improvement of the methodology. Furthermore, this study is also the first one to compare multisonic energy irrigation to other types of irrigation in presence of artificial internal resorptive defects. Considering the favorable performance of GW in removal of Ca(OH)2 in other scenarios of anatomic complexity in root canal system (21,25), the results of this study are significant for future directions in management of IRR. 5.2 Major findings First hypothesis The first null hypothesis was that the presence of resorptions (deep or shallow) as compared to no resorptions has no influence on the ability of different irrigation methods to remove calcium 49 hydroxide from the root canal system and resorptions. To the best of our knowledge, this hypothesis has not been tested in the literature as the most comparable studies did not have a canal with no resorptions as a control (20,82,83). Based on the findings of this study, this null hypothesis can be rejected as there was a statistically highly significant association between presence of resorption and calcium hydroxide removal (p<0.001). This result is unsurprising considering the difficulty in Ca(OH)2 removal by most irrigation methods from other challenging canal anatomy scenarios: C-shaped mandibular second molars (34), isthmi (21), and (an) artificial apical groove (33,79). Even when resorptions were not present the proportion of complete calcium hydroxide removal was only 33.3%, when all irrigation methods were considered collectively. This finding is in agreement with other authors, who demonstrated difficulty of calcium hydroxide removal from root canals without resorptive defects using conventional (32), sonic (77) and ultrasonic methods (34). Second and third hypotheses The second and third null hypotheses were that GentleWave irrigation system does not differ from other irrigation methods in effectiveness of removing calcium hydroxide from shallow (Ho2) and deep (Ho3) resorptions. These hypotheses have not been tested in previous studies. According to the results, both the second and the third null hypotheses can be rejected. A statistically highly significant association was detected between use of GW in removal of calcium hydroxide from deep and shallow resorptions compared to other types of irrigation (p<0.001). 50 The effectiveness of GW in Ca(OH)2 removal was previously demonstrated by multiple authors. Liu et al. (21) found that GW and PF were the only irrigation techniques that completely removed different formulations of Ca(OH)2 from artificial isthmi in a simulated 3D printed molar tooth model. Likewise, Ma et al. (25) showed that GentleWave removed significantly more Ca(OH)2 from mesial and distal canals of mandibular molars (100% and 98.78% +/- 3.84% respectively) than SNI and PUI systems. It is worth noting, that while in the present study GW was superior in Ca(OH)2 removal from both types of resorptions compared to other irrigation methods, it wasn’t able to clean Ca(OH)2 from the resorptions fully. In shallow resorptions GW was successful in total Ca(OH)2 removal in 98.3% of cases, however, in deep resorptions complete Ca(OH)2 was achieved only 41.7% of the time. These results could be in part due to the limitations of the 3D printed model. The dimensions chosen for the size of the shallow and deep resorptions allowed the model to be printed. After the models get printed, they need to be cleared of the support material, a process that proved to be extremely challenging according to SonEndo company who assisted with the 3D printing process. In order to clean the models, a long file was inserted to remove the support material from the canals and subsequently into the side vents to create a channel. The file was then used to break up as much support material within the resorptions as possible. After mechanical cleaning, the parts were soaked in lye and then pressure washed. This process was repeated multiple times over the course of a week and at the final stage, the parts were polished with 51 progressive sandpapers from 400-2000 grit and a buffing wheel with rouge. Reducing the measurements of the resorptions would have prevented the clearing of the model, making it unusable. As a tradeoff, the dimensions are larger than what is expected in a real-life situation. Subsequently, this also led to greater volume of calcium hydroxide and greater difficulty in its removal. Fourth hypothesis The fourth null hypothesis of this study was that composition of calcium hydroxide does not impact the ability of its removal from the root canal system and resorptions by different irrigation methods. A statistically highly significant relationship was found between the composition of calcium hydroxide and its removal by irrigation devices (p<0.001), therefore the fourth null hypothesis can be rejected. On the whole, UltraCal XS removal was more challenging compared to Multi-Cal with no calcium hydroxide removal obtained in 58.1% of UltraCal XS cases and 35.5% of Multi-Cal cases. There is a sparsity of literature on the removal of intracanal medicaments with differing calcium hydroxide composition (21). Mobarakeh et al. (20) has previously examined effectiveness of four different irrigation methods in removal of two different forms of calcium hydroxide from internal resorption cavities. The formulations of Ca(OH)2 they used were pure calcium hydroxide mixed with distilled water and Multi-Cal injectable calcium hydroxide paste. While the authors found a significant difference in the efficacy of irrigation methods, no statistically significant difference was found between the different compositions of calcium hydroxide in the removal of calcium hydroxide. They concluded that within the limitations of the study, addition of 52 substances such as methylcellulose and barium sulfate did not affect Ca(OH)2 removal by their irrigation methods. Liu et al.(21), on the other hand, did find a clear association between barium sulfate content and the ability of different irrigation methods to remove intra-isthmus calcium hydroxide in 3D models. Lambrianidis et al. (16) also assessed the effect of different Ca(OH)2 formulations on its removal efficacy by different irrigation techniques from single rooted extracted teeth. They compared Calxyl (Voco Praparate, GMBH. Dirmstein, Germany), Pulpdent paste (Pulpdent, Atertow, MA) and chemically pure calcium hydroxide mixed with sterile water. According to their results, the difference in calcium hydroxide concentration between the three medicaments did not affect its removal efficacy from the root canal system. However, contrary to the results of Mobarakeh et al.(20), Lambrianidis et al. (16) did find a statistically significant difference in calcium hydroxide removal between Pulpdent paste and pure calcium hydroxide. The authors argued the presence of methylcellulose in Pulpdent paste could influence its resistance to dissolution and removal by the different irrigation methods. In the present study Multi-Cal and UltraCal XS premixed injectable calcium hydroxide pastes were used. These particular formulations were chosen as they are commonly used in clinical practice. As per their manufacturer, Multi-Cal consists of 39% Ca(OH)2, aqueous hydroxyethylcellulose base, barium sulfate and UltraCal XS consists of <35% Ca(OH)2, aqueous matrix and <20% barium sulphate. As both Multi-Cal and UltraCal XS contain similar concentration of calcium hydroxide and are suspended in comparable water-soluble vehicle, it is possible the differences in the efficacy of their removal could be partially due to variation in their 53 barium sulfate content as shown by Liu et al. (21), some of the limitations of the 3D model as well as the method of removal assessment. The 3D printed transparent model used in this study was manufactured using PolyJet technology. Despite its accuracy, one of the consequences of this incremental layering technique is creation of a staircase effect. This can result in internal roughness of the material, making it more prone to staining. Over the course of this study, the same model was used 360 times to keep the tests reproducible and standardized. However, it cannot be ruled out that some degree of discoloration of the model occurred internally despite regular assessment under DOM and could have affected the accuracy of calcium hydroxide removal assessment. In this study, calcium hydroxide removal was assessed visually by giving the outcome a score of no removal, partial removal and complete removal. Many other ways to measure calcium hydroxide removal from the root canal system exist in the literature. Those include electron microscope pictures (30), light microscope pictures (16,32,78), spiral computed tomographic imaging (19), micro-CT imaging (25,34). Advantages of spiral computed tomographic imaging and micro-CT imaging are their ability to evaluate calcium hydroxide removal three-dimensionally, however, these methods are quite expensive. With an aid of image processing software, these methods could provide a more accurate and quantitative assessment of the calcium hydroxide removal compared to the methods used in the present study (83). 54 Fifth hypothesis The fifth null hypothesis was that location of resorption has no influence on the effectiveness of calcium hydroxide removal from the root canal system by different irrigation methods. This null hypothesis can be rejected as a statistically significant association was present between the location of resorption and calcium hydroxide removal (p<0.050), but it is worth noting it was not as high as the other tested factors (presence of resorption, depth of resorption, composition of calcium hydroxide). When all methods of irrigation were combined, middle resorptions displayed the greatest number of complete removal outcomes (20.4%), while apical resorptions had the lowest (14.6%). The majority of the studies on the calcium hydroxide removal from simulated resorption cavities are performed only in the apical third of the root canal (15,20,82). Similar to this study Yeter et al. (83) examined efficacy of calcium hydroxide removal from simulated internal resorption cavities at three different levels, but the authors only compared SNI and PUI as irrigation methods. Their main finding is in agreement with the present study: best calcium hydroxide removal results were achieved at the mid-root level of the tooth by both irrigation techniques. For the PUI the authors attributed this outcome to the highest displacement amplitude of the ultrasonic tip, but no explanation was given for the SNI outcome. One of the potential reasons why the location of the resorption was not as significant as other tested variables could be the difference in the operation of each irrigation technique. With syringe needle irrigation, both the open-ended and the close-ended needles were placed in the canal 1 mm short of the WL and then moved in 2-3 mm amplitude. Considering SNI has been 55 shown to have minimal displacement of particles past its needle tip (38), most of its effect was seen in the apical and middle parts of the root canal system and resorption. PF was placed inside the root canal 1 mm short of binding at 15 mm depth, which corresponded to mid-level portion of the root canal system. It was then activated and moved in 3-5 mm vertical strokes, while the irrigant solution was concurrently delivered at a rate of 15 ml/min. Placing the ultrasonic tip more apically would have resulted in direct physical contact of the tip with the canal walls and diminished acoustic streaming (60). But by keeping the tip at the suggested depth most of its action was seen in the middle resorption and canal level. EA was introduced inside the canal 1 mm short of the WL and then activated while moving the 25/04 polymer tip in 2-3 mm short vertical strokes with one solution replenishment stop mid-cycle. Although this technique follows manufacturer’s instructions, it resulted in the lowest irrigant volume compared to other irrigation methods. Baker et al. (47) showed that for the same type of irrigant, greater volumes were associated with better cleaning results. Low irrigant volume could explain why the action of EA was mostly limited to the coronal third of the canal. During GW use, degassed irrigation solution interacts with stationary fluid in the pulp chamber generating a strong shear force. Implosion of cavitation bubbles creates a broad spectrum of soundwaves which then travels apically through the irrigation solution within the root canal system (70). As a result of this action, the cleaning achieved with GW occurs in a coronal to apical direction. This outcome was seen in the present study, where coronal and middle 56 resorptions and parts of canal were cleaned earlier and more readily, than apical resorptions and canal. Sixth hypothesis The sixth null hypothesis stated that the type of irrigation system, presence of resorptions, location of resorption, depth of resorption, composition of calcium hydroxide has no effect on the efficiency of calcium hydroxide removal from the root canal system and resorptions. Presence of resorptions and depth of resorption were incorporated within one predictor – reverse resorption type. When the effect sizes among the four predictors (type of Ca(OH)2, GW vs other irrigation methods, location of resorption, and reverse resorption type) were compared through binary logistic regression analysis, all four predictors had a high effect on calcium hydroxide removal. Therefore, the sixth null hypothesis can be rejected. GW was found to have the highest effect size on successful calcium hydroxide removal – it was 99.5 times more likely to effectively clean calcium hydroxide from the root canal system and resorptions compared to other modes of irrigation. It is worth mentioning that the confidence intervals (CI) for this outcome were greater than anticipated (95% CI, 44.928 - 202.348), which could be indicative of a smaller than necessary sample size. Deeper resorption type, use of UltraCal XS and apical location of resorption were predictive of more difficult calcium hydroxide removal. These findings are in agreement with the results of the bivariate analysis. 57 Assessment of calcium hydroxide removal time Quantitative assessment of calcium hydroxide removal was only possible for two irrigation groups: PF 15 ml/min and GW. When the data was restricted to only contain cases with resorption, GW was the only irrigation method able to completely remove calcium hydroxide, albeit, not in every test. This study followed the manufacturer’s recommendations on maximum times to be used for each irrigation method: two minutes for SNI and PF, one minute for EA and six minutes fifteen seconds for GW. To account for the differences in maximum irrigation times between the test groups, the outcome was recoded as complete removal percentage. However, it cannot be ruled out that differing results could have been achieved if the maximum run time was kept the same for all test groups. This would have also potentially provided a greater sample size for a statistical analysis of numerical data. 5.3 Limitations In addition to previously discussed limitations of the 3D printed model, the qualitative nature of outcome measurement and the differences in maximum irrigation time between irrigation devices, a few other limitations of the present study are worth noting. Distilled water rather than an antimicrobial agent was used as the primary goal was to examine the mechanical effects of different irrigation devices on calcium hydroxide removal from root canal system and resorptions. GW has been previously shown to be still highly effective in calcium hydroxide removal even with water as an irrigant (25). In their review of the literature 58 on PUI, Van der Sluis 2007 (64) concluded that when used as an irrigant, water was less efficient than NaOCl during PUI. However, the studies they included to reach this conclusion only examined PUI irrigation in context of debris, pulp tissue and smear layer removal, and not Ca(OH)2 removal. Liu et al. (21) used distilled water, 0.5% and 3% NaOCl with SNI, continuous and intermittent flush PUI and GW and found no difference in the efficacy of these methods on removal of intra-isthmus calcium hydroxide. Another difference from true clinical situation is how long the calcium hydroxide was left inside the root canal system and resorptions prior to removal. In the present study, both premixed Ca(OH)2 formulations were removed immediately after placement. This permitted the data collection to be completed in a timely manner. When used in vivo, it is recommended to leave calcium hydroxide paste inside the canal for 1-2 weeks in non-perforating cases (2,22). For perforating cases, calcium hydroxide may be left for longer periods of time up to a year (2). Additionally, in the present study all syringe needle irrigation, including open-ended irrigation was placed within 1 mm of WL. It is highly unlikely that ONI at a flow rate of 15 ml/min would be used that far apically in a clinical situation due to the risk of potential apical extrusion and hypochlorite accident (21,46). 5.4 Future directions With the rapidly evolving 3D printing technology, it is anticipated that many of the limitations of the current 3D printed model will be overcome in the future. A hydroxyapatite-based matrix with similar physical properties to dentin has already been designed and printed for endodontic 59 simulation exercises (88). The printers are getting more and more sophisticated and able to print finer detail. Therefore, techniques to address the difficulties of support material clearing and irregularities of the multi-layer interface need to be developed. Some of the shortcomings of the study methodology should be targeted by determining the exact number of times the model can be used without any visible defects, by implementing a volumetric and quantitative methods of outcome assessment and using a larger sample size. Other types of irrigation (such as laser assisted irrigation and negative pressure irrigation) as well as irrigants commonly used in practice should be tested. 60 Chapter 6: Conclusion Within the limitations of the present study: 1. Presence of resorptions, depth of resorptions, use of UltraCal XS intracanal paste and apical location of the resorption were associated with greater difficulty of calcium hydroxide removal from the root canal system and resorptions. 2. 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Thesis/Dissertation
eng
Craniofacial Science
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Haapasalo, M. (Markus)
Effectiveness of different irrigation protocols in removing calcium hydroxide from simulated internal root resorptions
Text