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A retrospective review of implant treatment outcomes placed between 2009 and 2018 by the graduate periodontics… Almarzouki, Fatima 2020

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A retrospective review of implanttreatment outcomes placed between 2009and 2018 by the graduate periodonticsresidents at the University of BritishColumbia, Dental ClinicbyFatima AlmarzoukiB.D.S., King Abdulaziz University, Jeddah, KSA, 2012MSc. University at Buffalo, Buffalo NY, USA, 2015A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinThe Faculty of Graduate and Postdoctoral Studies(Craniofacial Science)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)January 2020© Fatima Almarzouki, 2020The following individuals certify that they have read, and recommend to theFaculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled:A retrospective review of implant treatment outcomes placed between 2009 and2018 by the graduate periodontics residents at the University of British Columbia,Dental Clinicsubmitted by Fatima Almarzouki in partial fulfillment of the requirements forthe degree of Master of Sciencein Craniofacial ScienceExamining Committee:Jolanta AleksejunieneSupervisorHannu LarjavaSupervisory Committee MemberGeorge GiannelisSupervisory Committee MemberDavid MacDonaldAdditional ExamineriiAbstractObjectives: This study was conducted to examine the rates and potentialpredictors of implant failures and peri-implant condition associated withtreatments provided by the periodontal residents at the graduate dental clinic atthe University of British Columbia (UBC).Materials and methods: A retrospective review of information from dentalcharts of patients who received dental implants at the UBC graduate clinic betweenJanuary 1st, 2009, and December 31st, 2018, by the graduate periodontics residents.Results: During the review period, 597 patients received a total of 1494 dentalimplants. The majority of potential risk indicators we examined did not havestatistically significant associations with either implant failures or peri-implantcondition.Conclusion: The implant failure rate was lower than the failure rate reported in aprevious retrospective study done in the same university setting. To ensure theproper documentation of all cases, the standardized protocol for informationrecording, including follow-ups, should be implemented.iiiLay SummaryThe current study examined the prevalence and the potential predictors ofoutcomes of implant-related treatments provided by periodontal residents at thegraduate dental clinic at the University of British Columbia. Two outcomes werechosen; implant failure (outcome 1: complete implant loss) and peri-implantcondition (outcome 2). A total of 597 dental charts of patients who received dentalimplants at the graduate periodontics clinic were retrospectively reviewed. Theoverall 4.6% failure rate of implants (outcome 1) was lower than the failure ratereported in a similar previous study done in the same university setting. Themajority of potential risk indicators we examined were not associated with eitherimplant failures or peri-implant condition. For future studies, the standardizedevaluation protocol should be used to assure that all necessary information for eachimplant case is recorded and properly documented.ivPrefaceThis study was approved by the University of British Columbia Clinical researchEthics Board (Certificate H18-00315). The dissertation is an original intellectualproduct of the author, Fatima Almarzouki, under the supervision of Dr. JolantaAleksejuniene. Fatima Almarzouki reviewed the dental charts and collected thedata, and Mr. Wei Zhan helped in acquiring patients’ information from theRomexis information system database. Fatima Almarzouki and Dr. JolantaAleksejuniene prepared the corresponding figures and performed statisticalanalyses. The committee members provided valuable feedback for the necessaryrevisions.vTable of ContentsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiLay Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiAcknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xivDedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv1 INTRODUCTION AND LITERATURE REVIEW . . . . . . . . . . 11.1 Implant therapy in dentistry . . . . . . . . . . . . . . . . . . . . . . . 11.2 Patient-related factors . . . . . . . . . . . . . . . . . . . . . . . . . . 5vi1.2.1 Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.2.2 Sex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.2.3 Smoking status . . . . . . . . . . . . . . . . . . . . . . . . . . 91.2.4 Systemic conditions . . . . . . . . . . . . . . . . . . . . . . . 121.3 Implant-related factors . . . . . . . . . . . . . . . . . . . . . . . . . . 141.3.1 Implant brand . . . . . . . . . . . . . . . . . . . . . . . . . . 141.3.2 Surface characteristics . . . . . . . . . . . . . . . . . . . . . . 161.3.3 Dimensions (width, length) . . . . . . . . . . . . . . . . . . . 181.3.4 Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.4 Site-related factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211.4.1 Bone quality in different arches . . . . . . . . . . . . . . . . . 211.5 Study rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.6 Research question . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231.7 Study aims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231.8 Study hypotheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . . 252.1 Inclusion and exclusion criteria . . . . . . . . . . . . . . . . . . . . . 252.2 Data collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26vii2.3 Study variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.3.1 Choosing implant treatment-related outcomes . . . . . . . . . 262.4 Potential predictors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.4.1 Patient level predictors . . . . . . . . . . . . . . . . . . . . . . 282.4.2 Implant level predictors . . . . . . . . . . . . . . . . . . . . . 292.5 Data management and statistical analyses . . . . . . . . . . . . . . . 293 RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.1 Patient-level analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . 303.1.1 Univariate statistics . . . . . . . . . . . . . . . . . . . . . . . 30Missing data . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Descriptive statistics . . . . . . . . . . . . . . . . . . . . . . . 323.1.2 Bivariate analyses . . . . . . . . . . . . . . . . . . . . . . . . 33Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Sex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Smoking status . . . . . . . . . . . . . . . . . . . . . . . . . . 35Systemic diseases . . . . . . . . . . . . . . . . . . . . . . . . . 373.2 Implant-level analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.2.1 Univariate statistics . . . . . . . . . . . . . . . . . . . . . . . 40viiiMissing data . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Descriptive statistics . . . . . . . . . . . . . . . . . . . . . . . 433.2.2 Bivariate analyses . . . . . . . . . . . . . . . . . . . . . . . . 46Arches of implant placement . . . . . . . . . . . . . . . . . . . 49Implant location . . . . . . . . . . . . . . . . . . . . . . . . . 50Implant Brand . . . . . . . . . . . . . . . . . . . . . . . . . . 52Implant width . . . . . . . . . . . . . . . . . . . . . . . . . . 52Implant length . . . . . . . . . . . . . . . . . . . . . . . . . . 55Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Bone quality . . . . . . . . . . . . . . . . . . . . . . . . . . . 564 DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 SUGGESTIONS FOR FUTURE STUDIES . . . . . . . . . . . . . . . 646 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67ixList of Tables1.4.1 Lekholm and Zarb classification for bone quality and quantity . . . . 213.1.1 Patient-level univariate descriptive statistics . . . . . . . . . . . . . . 313.1.2 Patient-level analyses: Implant failures (primary outcome) accordingto general health conditions . . . . . . . . . . . . . . . . . . . . . . . 403.1.3 Patient-level analyses: Peri-implant condition (secondary outcome)according to general health conditions . . . . . . . . . . . . . . . . . 413.2.1 Implant-level univariate descriptive analyses . . . . . . . . . . . . . . 423.2.2 Implant-level analyses: Implant failures and peri-implant conditionaccording to different follow-up periods . . . . . . . . . . . . . . . . . 483.2.3 Implant-level analyses: Implant failure rates according to differentimplant-related conditions . . . . . . . . . . . . . . . . . . . . . . . . 48xList of Figures2.3.1 Flow chart of patient-level outcome data . . . . . . . . . . . . . . . 272.3.2 Flow chart of implant-level outcome data . . . . . . . . . . . . . . . 283.1.1 Patient distribution according to the number of implants . . . . . . 323.1.2 Proportions of patients with failed implants . . . . . . . . . . . . . . 333.1.3 Implant-related outcomes (implant failure) in age groups . . . . . . 343.1.4 Implant-related outcomes (peri-implant condition) in age groups . . 353.1.5 Implant-related outcomes (implant failure) by sex . . . . . . . . . . 363.1.6 Implant-related outcomes (peri-implant condition) by sex . . . . . . 363.1.7 Implant-related outcomes (implant failure) by smoking status . . . . 383.1.8 Implant-related outcomes (peri-implant condition) by smoking status 383.1.9 Implant-related outcomes (implant failure) by presence of medicalconditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.1.10 Implant-related outcomes (peri-implant condition) by presence ofmedical condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39xi3.2.1 Implant distribution according to the arch . . . . . . . . . . . . . . . 433.2.2 Distribution of implants placed in maxilla (by teeth) . . . . . . . . . 433.2.3 Distribution of implants placed in mandible (by teeth) . . . . . . . . 443.2.4 Implant distribution according to implant location . . . . . . . . . . 443.2.5 Implant distribution according to implant type . . . . . . . . . . . . 453.2.6 Implant distribution according to implant width . . . . . . . . . . . 453.2.7 Implant distribution according to implant length . . . . . . . . . . . 453.2.8 Implant distribution according to torque at time of placement . . . . 463.2.9 Implant distribution according to the quality of bone . . . . . . . . . 463.2.10 Time of implant failure (months) . . . . . . . . . . . . . . . . . . . . 473.2.11 Implant failure by arch . . . . . . . . . . . . . . . . . . . . . . . . . 493.2.12 Peri-implant condition by arch . . . . . . . . . . . . . . . . . . . . . 503.2.13 Implant failure by location . . . . . . . . . . . . . . . . . . . . . . . 513.2.14 Peri-implant condition by location . . . . . . . . . . . . . . . . . . . 513.2.15 Implant failure comparison among 3 implant types . . . . . . . . . . 523.2.16 Peri-implant condition comparison among 3 implant types . . . . . . 533.2.17 Implant failure by implant width . . . . . . . . . . . . . . . . . . . . 543.2.18 Peri-implant condition by implant width . . . . . . . . . . . . . . . . 543.2.19 Implant failure by implant length . . . . . . . . . . . . . . . . . . . 55xii3.2.20 Peri-implant condition by implant length . . . . . . . . . . . . . . . 563.2.21 Implant failure by torque at time of placement . . . . . . . . . . . . 573.2.22 Peri-implant condition by torque at time of placement . . . . . . . . 573.2.23 Implant failure by quality of bone . . . . . . . . . . . . . . . . . . . 593.2.24 Peri-implant condition by quality of bone . . . . . . . . . . . . . . . 59xiiiAcknowledgmentsFirst of all, I want to express my sincere gratitude and gratefulness to my advisor,Dr. Jolanta Aleksejuniene, for her genuine support, untiring assistance, valuableadvice and words of encouragement throughout the course of this project.Besides my advisor, I would like to thank my thesis committee, Dr. HannuLarjava and Dr. George Giannelis, for their valuable feedback and constructivesuggestions.I extend my thanks to Mr. Wei Zhang, Senior Programmer/Analyst, for hiseffort and help in acquiring patients’ information from the Planmeca Romexis®database.My profound gratitude goes to my beloved parents, Eman & Sameer, for theirnonstop prayers and support. My soulmate and dear husband, Ismail, who hasalways been by my side during the difficult times. This journey would have notbeen possible without his continues support.And above all, I’m grateful to The Almighty God for his guidance, and forhaving made everything possible by giving me strength and courage.xivTo my angel babies, Salma & Basma:You didn’t leave alone; part of me went with you... You will forever be missed.To Maryam:Sometimes the little things in life take up the most room in our hearts. You are therainbow after the storm and the joy of my soul.xv1 INTRODUCTION AND LITERATUREREVIEW1.1 Implant therapy in dentistryDental implant is an accepted worldwide therapy employed to replace missing teethin partially or fully edentulous jaw and bears excellent results. For more than twodecades, the placement of dental implants has been steadily increasing in theUnited States. It is expected that implant treatments in dentistry continue to riseat a 12% annual rate [1]. The majority of dental implants worldwide areadministered in the United States, where 67.9% of periodontists, 89.6% ofmaxillofacial surgeons, and 12% of prosthodontists offer this to their patients [2].There are many reasons why dental implants are on the rise, including theincidence of tooth loss, poor performance and patients dissatisfaction with dentalprostheses, to obtain more predictable results after restorations with implants, tomeet the patient’s expectations and endorsement of implant therapy by specialists.An additional factor to consider is the recent advances in techniques andprocedures on the field [3]. The evolution of dental implants is evident, and theconcept of transosteal, subperiosteal and endosseous implants are now replaced byosseointegrated implants, which started to be used as a procedure after parallel1studies by Branemark and Schroeder in the 1970s [4] [5].Successful osseointegration of a dental implant is achieved when the vital boneshares a functional, structural and direct connection with the surface of the implantafter it is correctly set to function [5]. Under a new definition, osseointegrationrequires the formation of bone tissue with no fibrosis located in the biomechanicalunion of bone and implant. Thus, osseointegration between peri-implant bone andimplant is stable, firm, and long-lasting [6], and involves no interposition ofadditional tissue between the bone and the implant [7]. This approach ofosseointegration is shared by Brånemark [8], who describes a functional connectionbetween the surface of the implant and the patient’s bone through a tissue that ishighly differentiated. Osseointegration of implant is highly variable depending onthe patient’s age, health conditions, the size and shape of the of supra-structures aswell as other factors.It is also possible to improve the biological properties of the implant surfacesto favour osseointegration through various techniques [9]. The aim of thesetechniques is to stimulate osseointegration that especially thought to obtain fasterand stronger formation of bone in the area, improving the stability of the implantand a quick loading process [10].Surface chemistry of the bone and the implant along with topography studiesand modifications lead to improved osseointegration [11], and the dimension andtype of implant along with the surgical procedure play an important role as well. Itis also essential to determine the correct timing for implant placement and loadingto improve the survival rate of the dental implant [12, 13].Despite the variables mentioned above, the reported survival rate of dentalimplants is higher than 90% in a 5-year follow-up[14]. Even after such a highsurvival rate and the recent improvements in dentistry, technical, biologic and2esthetic complications may arise in some cases [15], and implant failure remains apossibility in a small subset of patients that is still significant to consider [16].Moreover, removing a failed implant endangers the final esthetic and functionalcomponent of the treatment and involves additional costs for the patient.It is essential to identify conditions associated with implant failures and informa patient, in order to make an informed decision and subsequently to refine thetreatment plan accordingly. [16]. For that reason, several clinical signs andradiographic parameters established as recommended standards to assess implantsuccess.Causes of implants failure can be divided into early and late causes. Amongearly causes are intraoperative trauma, contamination, overheating, an incorrectimmediate load, poor quality or quantity of bone tissue, and no sufficient stabilityof the dental implant. Among late cases are occlusal trauma, overloading, andperi-implantitis.Another factor that may compromise implant survival long-term is themarginal bone loss (MBL). In this regard, Albrektsson et al. [17] suggested in 1986that 1 mm of MBL is acceptable for the first year and 0.2 mm annually after thefirst year. Today, implant success is defined as a long survival rate with prosthesesstability, limited bone loss as shown by radiography, and no infection in the softtissues surrounding the implant area. These 4 criteria should be assessed toevaluate a healthy integration between bone and implant [17].In recent years, the gingival health index, plaque score evaluation, the absenceof bleeding and infection and the soft tissue contour have been introduced as extrameasures to assess dental implant success. Such variation in criteria to evaluateimplant success often makes systematic reviews and clinical studies difficult toevaluate against a standard guided by clinical evidence [14].3The aforementioned risk determinants can be further divided intoimplant-related and patient-related factors. The implant-related factors that wereassociated with implant failures are surface texture, loading and the dimension ofthe implants. Patient-related factors include a patient’s health status, his/herquality and quantity of bone, oral hygiene, smoking as well as generalhealth-related behaviours.The experience of a clinician may also play a role [18]. Kohavi et al. [19]reported that the clinician’s experience did not seem to be an influencing factor onimplant survival and observed that the cumulative implant survival rates were ashigh as 96% in cases where surgery was carried out by faculty-student teams.On the other hand, Lambert et al. study [20] reported that operatorexperience was an important factor related to the treatment outcome and foundthat implants placed by inexperienced surgeons failed more frequently as thoseplaced by experienced surgeons.Similarly, Preiskel et al. [21] reported that surgical experience plays animportant role in survival rates of unloaded implants. Seemingly, the implantfailure rate decreases with the increasing operator￿s experience. It has been shownthat the cumulative failure rate decreased from 6.0% to 3.0% [20].There have been many definitions of risk in the literature as well as theseterms were used in invariable ways by different authors. Different terms such as“risk indicator”, “risk factor”, “risk marker”, or “risk determinant” have often beenused more-or-less interchangeably [22]. Beck has listed definitions [23] that wereaccepted in the World Workshop on Periodontics in 1996: “the risk factor is anenvironmental, behavioural, or biologic factor which if present directly increases theprobability of a disease occurring, and if absent or removed reduces the probability.Once a disease occurs, removal of a risk factor may not result in a cure”. This4means that any definition of risk factor must evidently found that the exposure hasoccurred before the outcome. This in turn, means that only longitudinalprospective studies can identify risk factors. On the other hand, an exposure thatwas associated with an outcome in cross-sectional studies is called a risk indicator.Additionally, the terms used for the treatment-related outcomes differed indifferent studies. Implant survival refers to an implant that is still present at therecipient site, irrespective of whether it is currently in function, or has been buried.On the contrary, implant success refers to an implant that has parametersindicating its functionality in several ways [24].1.2 Patient-related factors1.2.1 AgeAge has been one of the most widely studied patient-related risk indicatorsassociated with implant success rate. It is not clear whether or not age relate toimplant failure, but it is still routinely examined along with sex, implant site,implant type, and other parameters, and it is ironically one of the most commonlyreported variable. Some studies reported that older ages do not significantlyincrease the likelihood of implant failure [25]. Still, it is known that the density ofbone, susceptibility to fractures, collagen synthesis and other bone proteins changewith advancing age, and it is expected to require a longer healing process in olderpatients after placing an implant [18].According to literature reviews of implant survival rates in older adults, age isnot a contraindication to suggest dental implants, but clinicians should understandthe medical complications, the slow healing process, and other psychosocial factors5that may affect implant prognosis is this age group [26].Shirota et al. (1993) studied osseointegration in young and older rats toevaluate the effect of ageing in the trabecular bone formed in the process. Inyounger rats, the authors reported the presence of new trabecular bone in theperi-implant area and more rapid contact in the bone-implant interface while olderrats displayed less bone to implant contact and reduced bone growth. This datasuggests that bone formation in the peri-implant area is reduced by age [27].Another study on younger and older rats showed lower bone-implant interfacecontact, reduced thickness in the bone contact area, and less bone tissue in thesurrounding area [28]. Thus, even if an older age is not considered acontraindication for dental implants, it is important to inform older patients aboutthe possibility of facing a less efficient healing process and reduced bone formationaround the surface of the implants, which ultimately may affect the rate of implantsuccess.According to a retrospective study comparing implant placement in youngerand elderly patients, long-term success in older patients was not significantly lowerthan that of younger patients [17].According to a recent retrospective cohort study by Papež et al. (2018), 47patients were followed-up for 7 years to assess dental implant osseointegration andthe differences between elderly populations and younger patients. As a result, theyreported there was no significantly different marginal bone loss between age groups[25]. Another study compared implant survival rate in 39 patients aged 60 to 74years old and 190 implants against 43 patients aged 26 to 49 years old and 184implants, all of them sharing similar types of prostheses and followed-up for 4 to 14years with no significantly different implant survival rates recorded [29].6Another study conducted in patients older than 80 years old with a total of254 implants showed an implant success rate of 96% with minimal complicationafter implant placement, similar to results found in younger populations. Marginalbone response in older patients resulted similar to that of younger patients, and theauthors of the study concluded that advanced age is not a reason to contraindicateor refuse dental implant treatment [30].A follow-up study performed between 1979 and 1999 in 464 patients withBranemark implants showed no significant differences between age groups whenadjusting for early implant failures [31]. Moreover, in a study published in 2005,Lemmerman concluded after examining 1003 cases of different implant designsbetween 1987 and 2002 that the success rate of implant therapy does not depend orcorrelate with the patient’s age [32].Another study published in 2005 by Moy et al. [16] followed a retrospectivecohort data of 21 years and 1,140 patients, all of them treated by the same surgeonand different implant systems. After examining the data, the authors reported thatolder patients had a higher rate of implant failure. Patients over 60 years old weretwice as likely to undergo complications after treatment with a failure rate of 18%against 9% in younger patients. Still, the authors concluded that older age shouldnot count as an absolute contraindication to deliver this type of treatment orconsider it as an option.A multicenter longitudinal study of 1022 implants over a period of seven yearsshowed that the cumulative implant success rate in patients over 60 years wasplaced in 78%. In patients, 40 years old and the younger success rate was 83% andpatients between 40 and 60 years had a cumulative success rate of 89%. In thisstudy, the authors did not use implant survival measures, and using implantsuccess criteria instead may account for the lower success rates [33].7A negative effect on implant treatment in older patients is not supported byconvincing evidence, but these age-related trials and studies have a commonshortcoming because they fail to evaluate age-related effects that truly affectimplant survival as an independent factor from general health deteriorationcommon in this age group, and which becomes a contributor in implant failurerates.Age by itself may not be a risk factor but its association with variables thatmight be contributing to increasing implant failure rates in the older population, asageing is usually associated with an increased number of patients with osteoporosis,diabetes and other medical conditions that may compromise the survival rate [14].1.2.2 SexStudies have reported significant sex differences in bone mineral density [34].According to a study performed in men and women cadavers by Baker et al., bothsexes had similar protein matrix levels per unit of segment volume, but womenshowed less bone mineralization in the skeleton, which was attributed to low levelsof calcium in females due to hormonal changes that typically arrive aftermenopause, which is possibly the case because the majority of cadavers examinedwere over 45 years old [35].No current clinical trials have reported sex-related differences in implantsurvival rate [36]. Even though there are no significant differences in survival rates,there is a difference in complications after the surgical procedure that affects thesuccess of implants. For example, there is a significant difference in coronalfractures, which is probably explained by a different occlusal force between sexes,and there is also evidence that post-menopausal women have decreased bonequality compared to men of a similar age, and this potentially could lead to more8peri-implant complications [37].1.2.3 Smoking statusSmoking is the most common risk factor for multiple diseases and premature deathworldwide. It is estimated that smoking accounts for approximately 4–5 milliondeaths annually. This number is expected to increase to approximately 10 million ayear by 2030 [38, 39].Cigarette smoke contains about 4000 chemical agents, including over 60substances that are known to cause cancer in humans, defined as “carcinogens”[38].Studies demonstrated that these chemicals can damage DNA and change geneexpression. Due to these chemicals, a cascade of these molecular changes may leadto malignancy. Smoking has been associated with at least 14 different types ofcancer. A relationship has been established between cigarette smoking and multiplediseases such as lung cancer, different cancers in the oral cavity, pharynx, larynx,breast, pancreas, urinary bladder, colon, renal pelvis, urethra and cervix [40].In addition to the well-recognized damaging effects of smoking on respiratory,cardiovascular and other systems, tobacco use has substantial harmful effects onoral health and it has been associated with several oral and perioral healthconditions including cancer, premalignant lesions, periodontitis, tooth loss, implantfailures, dental caries and other conditions [38].The local effects of smoking on the periodontium consist of gingival mucosalirritation, altered salivary flow and microbial changes, while systemic effects includealtered immunological activity, vasoconstriction and bone destruction. Thesedetrimental effects result in loss of alveolar bone, which cumulatively results in apermanent increased risk for tooth loss [41].9Smoking has also been reported in several studies as one of the main riskfactors for implant failure [31, 42]. Nicotine is cytotoxic to gingival fibroblasts byreducing their proliferation [43]. It also impairs osseointegration, resulting indeposition of fibrous tissue at the bone–implant interface [44]. Daily administrationof 0.93 mg/kg of nicotine caused a dramatic decrease in the percentage ofbone–implant contact after 42 days of implant insertion in rabbits [45]. Smokingmay also change the density and quantity of bone formed around the implant afterinsertion. [46]The effects of smoking on implant success rates are more significant whenthere’s an area of poor bone quality. For instance, studies show that smokers havea higher failure rate in maxillary implants compared to mandibular implants[47, 48]. Other studies have demonstrated the effect of nicotine as a vasoconstrictoras a significant risk factor leading to implant failure [49]. This association may beone possible explanation for the reduced failure rates of implants placed in theposterior mandible of smokers because this area is more protected against tobaccosmoke due to the presence of the tongue [50]. Other studies show that smokingdoes not influence osseointegration. Thus, the negative effect of this risk factor maystart after the second-stage period of surgery. Consequently, a study conducted byGorman et al. [49], analyzing data of more than 2000 implants, showed thatimplant failures were more common in smokers after the second-stage period ofsurgery.Another study by Lambert et al. [51] reported an increased rate of failuresamong smokers is more common after the uncovering phase and before insertingthe prosthesis. Thus, the authors concluded that tobacco smoking affects thehealing process differently after tooth extraction versus implant placing becauseafter tooth extraction implant wounds are still open, and the intimate relationshipbetween bone and implant does not allow for the interference of vasoconstriction by10the nicotine, which affects the healing process. Conversely, when the implantsremain uncovered, the surrounding tissue becomes affected by tobacco exposure ina similar way to periodontal tissues. Thus, the reason why implant failure increasesin tobacco smokers is not because of reduced osseointegration but as a result of theexposure of peri-implant tissue to nicotine and other substances in tobacco smoke.According to a study of collected salivary samples by Queiroz et al. [52], 41subjects were analyzed for salivary arginase activity by measuring the levels ofl-ornithine. The authors reported increased activity of salivary arginase in smokerswith dental implants compared to non-smokers with dental implants. Subsequently,more arginase activity in the saliva leads to lower levels of nitric oxide production,which makes patients more susceptible to bacterial infections and increases the riskof implant failure.Thus, it is known that there is a higher complication rate of implant therapy insmokers, and it has been found that smoking leads to more marginal bone loss afterplacing the implant and increases the risk of peri-implantitis as well. Moreover, thefailure rate of implants among smokers was twice as high as that of non-smokeraccording to studies [48, 53]. The higher rate of marginal bone loss among smokersis located in the maxilla [54]. According to research performed by Levin [55] et al.,smokers had an increased marginal bone loss compared to ex-smoker, but bothgroups displayed a higher marginal bone loss when compared to non-smokers.Studies by Lindquist et al. [56] reported an increased level of marginal boneloss in smokers, but this finding was not linked to a higher rate of implant loss overa period of 10 years. Conversely, patients with poor oral hygiene who were alsosmokers displayed three times greater marginal bone loss compared to non-smokersover a period of 10 years.It is possible to increase the implant survival rates in smokers following various11important recommendations. According to Bain and Moy [57], smokers shouldcease smoking for 1 week or more before the surgery. This period is sufficient toreduce the short term effect of nicotine. Tobacco avoidance should be continued forat least 2 months after implant placement because only after this time bone healingwill be enough to complete the osteoblastic phase and well-establishedosseointegration.1.2.4 Systemic conditionsOsteoporosis is a common condition that impacts over 30 million women aftermenopause in the U.S. [35]. Women are most susceptible to osteoporosis because ofthe decreased level of estrogen associated with menopause. The decreased level ofestrogen is associated with an increase in the level of cytokines (either directly orindirectly) that modulate osteoclasts activity including RANK ligand (RANKL)and osteoprotegerin (OPG). RANKL binds to RANK receptors, found onosteoclasts, which causes them to activate and proliferate, leading to an increase inbone resorption in normal bone modelling and remodelling and in diseasescharacterized by increased bone turnover [35]. OPG binds to RANKL and preventsexcessive bone resorption by preventing it from binding to RANK. Thus, theconcentration of RANKL and OPG in bone is a major factor in determining thebone mass and strength [58].In some skeletal diseases, including postmenopausal osteoporosis,hyperparathyroidism, and rheumatoid arthritis, there is an increase in the rate ofbone remodelling and the number of remodelling sites that induce bone resorptionby up-regulating the expression of RANKL by osteoblasts and other cells [59, 60].Increases in implant failure with postmenopausal osteoporosis have not beenreported [61]. However, August et al. emphasized the importance of estrogen status12after menopause by reporting that post-menopausal women with no hormonereplacement therapy had a decreased healing rate, especially in the area of themaxilla [62].Diabetes is a metabolic disease that alters tissue integrity, impairs woundhealing, and increases susceptibility to infections [63]. Tissue hyperglycemia affectswound healing by negatively affecting the function, chemotaxis and phagocytosis ofneutrophils and lymphocytes. It is also associated with delayed wound healing andcompromised response to infection [63]. Hyperglycemia also inhibits theproliferation of osteoblasts and the production of collagen during the early stages ofcell development. This results in a reduction in bone formation and a reduction inthe mechanical properties of the newly formed bone [64]. Well-controlled diabeticpatients are usually suitable for implant therapy, while poor glycemic control isconsidered as a relative contraindication for implant therapy [63].However, most studies describe patients with diabetes as ‘well-controlleddiabetic,’ but authors do not usually report how glycemic control was assessed [65].Siqueira et al. inserted implants into the tibiae of diabetic rats. Histological andhistomorphometric analysis of bone-implant sections were performed and showed a50% reduction in the area of formed bone. They reported decreased levels ofimplant osseointegration in animals with untreated type1 diabetes [66].Tawil et al. studied implants with immediate loading in 58 well-controlleddiabetic patients. No failure was observed after a mean follow-up of 42 months [67].Similarly, another study reported that glycemic control not significantly related toimplant survival over 5 years in 58 patients with well-controlled diabetic patientswho received mandibular implants [68].Oates et al. showed that patients with Hemoglobin A1c test (HbA1c)  8.1%had a greater decrease in implant stability from baseline and required a longer time13for healing [69]. However, a study by Dowell observed that compromises inglycemic control might not affect implant success in humans [65].1.3 Implant-related factors1.3.1 Implant brandThere are many different choices of dental implants brands that have been evolvingfor more than 30 years and now offer many different types according to size,surface, and other features. It is possible to choose from over 2,000 implants, and itis important to evaluate the claims made by manufacturers and implant companiesin an evidence-based setting. However, after reviewing the scientific literature onthe matter, there is no systematic review currently available to guide the clinician’schoices and give reliable evidence on implant systems available on the market.It is difficult to make an evidence-based comparison of implant systems withthe available literature because they are reported in separate studies with differentmethodologies, are usually from patient groups from different clinics or treated bydifferent professionals with variable technical performances and indications.Reliable comparisons should be made by grouping patients with the same implantsystem and treated by the same therapeutic team.Batenburg and colleagues studied implants in the edentulous mandible treatedwith overdentures, using ITI, IMZ, or Branemark systems [70]. After 12 months,the gingival recession increased significantly in the Brånemark and IMZ group, andthere was significantly less bone loss in the ITI group. This study concluded thatthe ITI implant appears to be the implant of choice for mandibular overdenturetherapy.14A study by Kemppainen et al. evaluated Astra Tech Dental Implant Systemand IT1 implants in a 1-year study of patients with single-tooth implants [71].They found that marginal bone loss wasn’t significantly different between Astraand ITI dental implants during the study period. The study demonstrated that theshort-term survival rates of both implant systems that supported single-toothcrowns were excellent.Another comparison between the Branemark System and Astra Tech implantswas made by van Steenberghe et al. in patients with partially edentulous mandibles[72]. No significant differences were found concerning probing depths, presence ofplaque or change in marginal bone level. The survival rates of 100% for the AstraTech system and 97.7% for the Branemark System were not statistically different.The most commonly used implant systems to date are the Branemark Systemand ITI Dental Implants. According to a comparative study between ITI DentalImplants and the Branemark System over a 3-year follow-up to treat partiallyedentulous maxillae, there were no significant differences between each brand,except for a higher incidence of peri-implantitis in ITI Dental Implants. Bothdisplayed a high survival rate of over 97% and a small marginal bone loss rangingbetween 1.3 and 1.8 mm [73].Conversely, Meijer et al. reported in 2009 that ITI Dental Implants showed ahigher survival rate in comparison with Nobel Biocare Implants (100% and 98%,respectively) [74].French et al. evaluated the long-term survival of anodized surface NobelBiocare [75] and Straumann dental implants [76] placed in a private practicesetting with up to 10-year follow-up. They found that the cumulative implantsurvival rate for the Nobel Biocare implants after 10 years was 97.0% and forStraumann implants, it was 98.4% at the 7 years follow-up.15Other studies have shown that Branemark Nobel Biocare System wieldedresults below the average while other implant systems, including the ITI DentalImplant System and Astra Tech System implants, showed results above the average[77].Similarly, Derks et al. [78] found significantly higher odd ratios forperi-implantitis in patients treated with the Brånemark and Astra Tech implantsystems when compared with the patients treated with the Straumann implantsystem. This difference could be due to the differences in the implants used;Straumann implants at the time of this study were tissue-level implants while theNobel and Astra implants were bone-level implants. However, this study didn’tprovide information about the brand-specific criteria that can lead to or preventperi-implantitis.1.3.2 Surface characteristicsImplant surface topography has been thought to influence the implant-boneosseointegration, impact the peri-implant bone level and consequently may affectthe incidence of peri-implant diseases . Thus, in the last two decades, manyimplant system with different surface texures were introduced [79].Multiple surface modifications of implant have been made. The modificationmethods can be either a subtractive or an additive modification. The subtractivemethods include a removal of material from the implant surface, while the additivemethods requires addition of material [80]The earlier studies evaluating the machined-surface (smooth-surface) implantsreported higher failure rates. In addition, these studies did not assess the bonequality and other parameters now considered as important factors. However, it is16important to consider that the majority of failures were related tomachined-surfaced implants that also were placed in anatomic areas with poor bonedensity [79]. A review of the scientific literature by Renouard and Nisand reporteda trend to use machined-surface implants for patients displaying an increased rateof bone loss, which is not applicable for TiUnite and other rough surfaces [13].Their statistical analysis revealed no significant difference in failure rates after usingmachined surface implants against TiUnite surface implant, but more implant losswas found in machined-surfaced implants [81]. This increase in implant loss wasprimarily associated with other factors such as poor bone density, the preparationand design of the implant, and the fact that this type of implant is often used as arescue measure when the use of rough-surfaces implants was not possible.A consensus meeting of the European Federation of Periodontology in 2008examined the available literature and found that marginal bone was preserved withsurface-modified implants. Nevertheless, there was no clinically significantsuperiority for any specific implant surface or design [82].A study in 2005 [83] radiographically assessed marginal bone loss andperi-implantitis between several implant systems with different implant surfaces. Itwas concluded that there were no statistically significant differences in implantfailures among the different systems.However, some recent studies reported lower bone loss with rougher surfacesthan with smooth ones. Polizzi and co-workers retrospectively comparedBranemark implants (minimally rough machined-surface) with TiUnite implants(moderately rough). The cumulative survival rate for Branemark implants was90.3%, whearse for TiUnite implants it was 96.6%. This clearly demonstrate thatthe survival of implants improved significantly with the rougher surfaces [84] .Another study by Renouard and Nisand [13] also showed an improvement in17survival rate when using oxidized implants instead of machined-surfaced implants,but the difference reported in this study was 5% and not statistically relevant.A limitation of all these studies is that implants do not differ in surfacetextures only. They differ in multiple aspects such as implant design, type ofsupra-structure, loading and loading time. Therefore, it is very difficult to concludeto what extent surface texture alone is attributed to bone loss.1.3.3 Dimensions (width, length)Implant length is a controversial risk indicator for implant survival. The high ratesof short implant failure were reported in earlier studies. At that time, theplacement of dental implants was performed with routine surgical procedures,usually not considering the bone quality, with machined-surfaced implants and inrestricted anatomic sites with poor bone density. These studies reported thatshorter implants have an increased rate of implant failure. [85–90].On the other hands, other authors reported that survival rates are appropriatein both short and long implants and that there is no influence whatsoever in thesurvival rate depending on implant length [33, 91, 92]Two studies in 2000 and 2001 showed that short implants provide a similaroutcome compared to longer implants, and the survival rate was maintainedbetween 88 and 100% [93, 94]. Cruz and colleagues found no significant differencein the survival rate between short (length < 8.5 mm) and longer implants or in theamount of marginal bone loss (p = 0.86). However, the rates of biologicalcomplications for long implants associated with maxillary sinus augmentation werehigher (p < 0.001), whereas the prosthetic complications were higher for shortimplants (p = 0.010) [95].18In regard to implant width, a study by Ivanoff et al. [96], reported higherfailure rates for 5-mm-diameter. These failures were associated with the learningcurve of the operator, and other factors such as insufficient bone density, thepractice of using these implants as a rescue treatment, the design of the implantand the use of this size when a standard diameter was not stable enough. This datawas further supported by an investigation published in 2004 [97], where the authorsreported a similar trend of frequent implant failures of wider implants. Differentstudies reported that wide-diameter implants were usually placed in anatomicalareas with poor bone density, the compromised volume of bone, and otherunfavourable clinical settings [96, 98].1.3.4 TorqueThe primary stability of an implant can be defined as the stability of an implantimmediately after insertion [99]. This feature is associated with the micro-motion,and it has been considered an important factor in predicting the osseointegration ofan implant and the success of implant therapy. There is no current consensus onwhat the minimal torque should be to guarantee a successful implant, but cliniciansoften use a torque of 20 to 40 Ncm [100]. Implant insertion torque depends onmany different factors, especially the quality of the bone at the osteotomy site, thepreparation technique of the osteotomy site, the morphology and geometry of theimplant, and the initial implant-to-bone contact [101].In a recent systematic review, the authors stated that an increased level ofimplant stability (which is measurable through the insertion torque) is to beincluded as a requisite for a successful immediate or early loading of implants. Thisis why many authors have highlighted the importance of insertion torque measuresto offer predictive values for implant success [102].19Still, it is important to remember that the ultimate goal of implant dentistry isto achieve secondary stability by biologic means. Thus, a very high initial insertiontorque, which is the focus of the design in many types of implants, might becomecounterproductive and endanger early osseointegration.Studies report high survival rates in implants loaded or provisionalizedimmediately and with very low insertion torques [103, 104]. According to datagathered by Toljanic et al., 38% of studied implants showed an insertion torquelower than 20 Ncm, and only 12% of them were lower than 10 Ncm. As aconclusion, the authors stated that even if primary stability is an important factorin achieving implant success, many others should be at play at the same time,which explains why many implants with low insertion torque achieve successfulosseointegration after an immediate functional loading [104].A study conducted by Duyck et al. [105] compared marginal bone loss data invarious implants placed with low and high torque and showed that insertiontorques higher than 40 Ncm had significantly higher levels of marginal bone loss asmeasured in the cortical crest. Another study published by Aldahlawi et al.reported that insertion torques higher than 55 Ncm had more remodelling area inperi-implant bone compared with lower insertion torques, thus concluding that thelocation of implants in the jaw and bone density modulate insertion torque [101].Finally, data from Al-Nawas et al. suggest that maximum insertion torque is notdifferent between successful and failed implants and do not have any statisticalsignificance [102].20Table 1.4.1: Lekholm and Zarb classification for bone quality and quantityBone quality1 Entire jaw is cortical bone2 Thick cortical bone surrounds a core of dense trabecular bone3 Thin layer cortical bone surrounds a core of dense trabecular bone4 Thin layer cortical bone surrounds low-density trabecular boneBone quantityA The alveolar ridge is intactB Moderate ridge resorption has occurredC Advanced residual ridge resorption has occurredD Some resorption of the basal bone has begunE Extreme resorption of the basal bone has occurred1.4 Site-related factors1.4.1 Bone quality in different archesAnother variable commonly addressed is bone density. This risk indicator has beenpointed out to impact osseointegration of implants [106].The classification system of quantity and quality of jaw bone dates back from1985, when Lekholm and Zarb created a classification of bone quality from 1 to 4and bone quantity measured from A to E, as seen in Table 1.4.1 [107]. It is to datethe most widely used classification to evaluate the bone quality and quantity in aclinical setting [108].Many authors demonstrated that the poor quality and severe resorption ofjawbone negatively affect implant survival [109–111]. A 2007 systemic reviewreported that the implant survival for the mandibular fixed prosthesis was by 6.6%larger than the survival for the maxillary fixed prostheses implants (P < 0.001).The observation of greater implant failure for removable over fixed protheses groupsin the maxilla may be due to insufficient preoperative bone volume in the group of21patients with removable prostheses [112].Herrmann et al. [86] evaluated the risk of implant failure in relation to severalcombinations of bone quantity and bone quality. Combining these 2 bone factorsresulted in four different subgroups as follows; a combination I patients with goodbone quantity (A, B or C) as well as good bone quality (1, 2, or 3). Combination IIpatients with good bone quantity (A, B, or C) with poor bone quality (4)Combination III patients with poor bone quantity (D or E) with good bone quality(1, 2, or 3) Combination IV patients with poor bone quantity (D or E) with poorbone quality (4). There was a highly significant correlation between bonequantity/quality and implant failure. The failure rate in combination IV patients(patients with the most resorbed and porous jawbone situations) was statisticallyhigher compared to all other combinations (%65 of patients with this combinationexperienced implant failure), wherein combination I, only 1 in 20 patientsexperienced an implant failure. Moreover, in combinations II and III (when only 1of the bone-related factors was good), the good factor appeared to compensatepartly for the less-good one.Caution should be taken when comparing results from different studies. Forexample, the cumulative survival rate of 96% in poor bone density that wasreported by Feldman et al. [92] and the 94.6% reported by Renouard and Nisand inthe severely resorbed maxilla [13] should not be compared with survival rateachieved with implants placed in areas with an adequate bone density.1.5 Study rationaleThe understanding of different risk indicators determining implant failures orimplant-related diseases is of key importance to treatment planning, informed22patient consent as well as improving professional education in order to make aninformed decision and subsequently to refine the treatment plan accordingly. Inaddition, there has been no recent review of the treatment outcomes at UBC aftera previous study reviewed implants placed between 1989-2006. Therefore, thecurrent study aimed to gather additional evidence about the determinants oftreatment outcomes at UBC.1.6 Research questionTo evaluate outcomes of implant treatments provided and followed for differenttime periods by dental residents in a post-graduate educational setting: thegraduate periodontal dental clinic at the Faculty of Dentistry, University of BritishColumbia (UBC).1.7 Study aims• To examine the outcomes of implant treatments provided by periodontalresidents at UBC graduate clinic.• To compare the implant treatment outcomes of the present sample to aprevious report about a similar sample and a similar clinical setting.• To identify predictors of implant failures (primary outcome) and peri-implantcondition (secondary outcome) where implants were placed by theperiodontal residents.231.8 Study hypotheses• Primary (implant failure) and secondary outcome (peri-implant condition) ofimplant treatments present slightly different trends, where the prevalence ofthe primary outcome is lower than the one of the secondary outcome.• The implant failure rate is relatively high in patients treated by periodontalresidents at the graduate dental UBC clinic but similar to the failure rateobserved in a similar previous study.• Both primary and secondary outcomes of implant treatments are associatedwith several patient-related and implant-related indicators.242 MATERIALS AND METHODSA retrospective chart review of patients who received dental implants at thegraduate clinic of the University of British Columbia (UBC), Vancouver, Canada,was performed. The study was approved by the UBC Clinical Research EthicsBoard (H18-00315). All data analyses were performed on the de-identifiedinformation. The study reviewed the outcomes of implant treatments providedbetween January 1st, 2009, and December 31st, 2018, by the residents of the UBCgraduate periodontics program.2.1 Inclusion and exclusion criteriaThe inclusion criteria:Dental records comprising information about one or more dental implants thatwere placed by the residents of the graduate periodontics program between January1st, 2009, and December 31st, 2018.25The exclusion criteria:Implant placed before January 1st, 2009, and December 31st, 2018.2.2 Data collectionThe patient demographic data, surgical and follow-up information were extractedfrom the health history questionnaire, periodontal charting odontogram, andsurgical progress notes in the electronic patient dental charts (Planmeca Romexis®3.8.3.R, Helsinki, Finland).2.3 Study variables2.3.1 Choosing implant treatment-related outcomesMost published studies used several criteria to determine the success of implanttreatment which usually included: no implant mobility, no peri-implantradiolucency, less than 0.1-0.2 mm of annual bone loss after the first year, absenceof signs and symptoms such as pain, infection, neuropathies or paresthesia, etc.[17, 19, 24, 113].Implant success refers to the implant that has parameters that indicate itsfunctionality in several ways. On the other hand, implant survival refers to animplant still present at the recipient site, irrespective of whether it is currently infunction, or has been ‘buried.’ Due to various definitions of implant success,authors usually report data on implant survival in combination with the incidenceof complications.In the present study, the use of such success-related criteria was not feasible,26Figure 2.3.1: Flow chart of patient-level outcome dataas medical charts did not contain such information. For example, the follow-upexams at UBC do not routinely consist of removal of any fixed splintedimplant-supported restorations, and hence, do not allow for a true assessment ofthe mobility of each individual implant. The UBC does not have a standardizedprotocol for reporting information related to follow-ups; therefore, a comprehensiveassessment of implant-related success was not feasible.Figure 2.3.1 and 2.3.2 present flow charts of how information was collected forthe two levels of analyses, namely the extraction of information for the patient-leveland the implant-level analyses.As in other retrospective studies [114–116], our choice for the primary outcomewas ‘implant failure’ where failure was defined as the loss, removal or need forremoval of an implant at any time. The secondary outcome we chose wasperi-implant condition, and we defined it as an implant with any of the following:bleeding upon probing (BOP), increase in periodontal pocket depth (PD) morethan 1 mm or increase in gingival recession (GR) more than 1 mm from baseline.27Figure 2.3.2: Flow chart of implant-level outcome data2.4 Potential predictorsTwo levels of potential risk indicators for implant failure were considered: patientlevel and implant level. A number of patient-level and implant level predictors weretested in relationship to both study outcomes.2.4.1 Patient level predictorsBased on what was reported on dental records, patients were divided into three agegroups: the youngest group (less than 50 years old), middle-age group (51-65 yearsold) and the oldest group (65+ years old) and regarding smoking: current, formeror never smokers. Information about several systemic conditions was also collectedfrom dental charts, and the presence of the following systemic conditions wasreported: the presence of cardiovascular diseases, diabetes, gastrointestinal diseases,psychological disorders and orthopedic diseases.282.4.2 Implant level predictorsThe following potential risk indicators for implant failures were evaluated: implanttype (brand), implant dimensions (width, length), arch in which implant was placed(maxillary, mandibular), implant location within the arch (anterior, posterior), thetorque and the quality of bone, all evaluated at the time of the implant placement.Three brands of implants have been used in the dental graduate periodontics clinic,namely Branemark/Nobel, ITI/Straumann, and Dentsply Sirona. The implantwidth was classified as narrow (3.3 mm - 4.0 mm), regular (4.1 mm - 4.3 mm), orwide (4.8 mm - 5.5 mm). According to the length, implants were grouped as short(6.0 mm - 9.0 mm), long (10.0 mm - 12.0 mm), or very long (> 12.0 mm). Thetorque of implants was defined and measured at the time of their placement usingthe torque wrench or the handpiece for the implant placement. The torque wasrecorded as follows: low (< 25 Ncm), medium (25 Ncm-35 Ncm) and high (> 35Ncm). The quality of bone was measured by the resident at the time of the implantplacement, and bone was classified into soft, medium or dense.2.5 Data management and statistical analysesAll statistical analyses were performed employing the SPSS Version 25.0 software,and the level of significance for all tests was set at p < 0.050. Univariatedescriptive statistics described the sample distribution regarding the two studyoutcomes and their potential predictors. Bivariate analyses tested a number ofpotential risk factors (predictors) for both study outcomes. Bivariate statistics wereperformed employing the Chi-square test at the patient and the implant levels.293 RESULTSThe study retrospectively reviewed information from dental charts of 597 implantpatients that were available in the UBC electronic chart filing system. Thesepatients received a total of 1494 implants.3.1 Patient-level analyses3.1.1 Univariate statisticsThe sample description and details about missing data at the patient level arepresented in Table 3.1.1 and the descriptive statistics at the implant level in Table3.2.1.Missing dataThe current study identified missing data in some patient-related information, asshown in Table 3.1.1. The demographic information regarding the patient’s age andsmoking status were reported in all dental charts (100%).30Table 3.1.1: Patient-level univariate descriptive statisticsVariables N (valid %)a Missingb N/N total (%)Age groups18-50 years 101 (16.9)0/597(0.0)51-65 years 238 (39.9)65+ years 258 (43.2)SexMales 326 (54.7) 1/597(0.16)Females 270 (45.3)Smoking statusNon-smoker 322 (53.9)0/597(0.0)Former smoker 158 (26.5)Current smoker 117 (19.6)Presence of medical conditionsCardio diseases 296 (49.6)Diabetes 85 (14.2)Gastro diseases 161 (27.0)Psychiatric diseases 102 (17.1)Orthopedic diseases 250 (41.9)a Percentages calculated from valid data.b Missing data could not be calculated for medical conditions.31Descriptive statisticsThe cohort of implant patients (Table 3.1.1) included 54.6% males and 45.2% offemales with a mean ± sd age at the implant surgery of 60.7 ± 12.7 years.Patients’ age ranged from 18 to 87 years old. Of all 597 patients, 16.9% were under50 years of age, 39.9% were between 51-65 years of age, and 43.2% were older than65 years. Of all, 53.9% of patients had never smoked, 26.5% were former smokers,and 19.6% were smoking at the time of the implant placement.The majority of patients, 238 out of 597 (40.0%) had one implant, 176 patients(29.5%) had two implants, and 183 patients (30.5%) had three or more implants(Figure 3.1.1).Figure 3.1.1: Patient distribution according to the number of implantsOut of 597 patients that were included in the study: 541 (90.6%) had notexperienced implant failure (primary outcome), forty-six patients (7.7%) had atleast one implant removed, and ten patients had two or more implants removed(1.7%) (Figure 3.1.2).Substantial information was missing regarding the implant condition-relatedinformation (secondary outcome). Consequently, subsequent analyses had to bedone with fewer patients (N=489). Implant failures (primary outcome) were32Figure 3.1.2: Proportions of patients with failed implantsobserved in 56 patients (9.4%) who had one or more implants removed. Regardingthe implant condition (secondary outcome), 26 patients had no peri-implantcondition (5.3%), and 463 patients (94.7%) had peri-implant condition. There wasno sufficient information (due to missing information) to define peri-implantcondition status in 108 patients (18.1%).3.1.2 Bivariate analysesFor ease of comparison, further results will be presented for both outcomes, first forthe implant failure (primary outcome) and then for the peri-implant condition(secondary outcome).AgeThe percentage of patients with implant failures (primary outcome) in the youngestgroup was 9.9%; in the middle age group, it was 9.7%, and in the 65+ years oldgroup, it was 8.9% (Figure 3.1.3). These age-related differences in implant failurerates were not significant (Chi-square test, p=0.942). The percentage of patientswith the peri-implant condition (secondary outcome) in the youngest group was33Figure 3.1.3: Implant-related outcomes (implant failure) in age groups93.3%, in the middle age group 93.5%, and in the 65+ years old group, it was96.3% (Figure 3.1.4). There was no significant difference in the rates ofperi-implant condition (secondary outcome) among different age groups(Chi-square test, p=0.378).SexAmong males, 28 patients (8.6%) had at least one failed implant (primaryoutcome), and 249 patients (93.3%) had peri-implant condition (secondaryoutcome). Similar results were observed for females, where 28 females had at leastone implant failed (10.4%), and 214 females (96.4%) had the signs of peri-implantcondition (Figures 3.1.5 and 3.1.6).There were no statistically significant sex-related differences in the implant34Figure 3.1.4: Implant-related outcomes (peri-implant condition) in age groupsfailure rates (Chi-square test, p=0.458) or in the rates of peri-implant condition(Chi-square test, p=0.121).Smoking statusGiven that the information when smoking was quitted was not available for themajority of patients, it was not possible to compare these subgroups of patients inindependent analyses. Thus, current and former smokers were joint in one group.Patient distribution, according to implant failure, is presented in Figure 3.1.7.Implant failure rates (primary outcome) were more common among thenon-smokers than among the joint current/ former smokers. Thirty-threenon-smokers (10.2%) experienced implant failures, while 23/275 (8.4%) offormer/current smokers experienced implant failures, but these differences were notstatistically significant (Chi-square test, p=0.431). In the joint current/ former35Figure 3.1.5: Implant-related outcomes (implant failure) by sexFigure 3.1.6: Implant-related outcomes (peri-implant condition) by sex36smokers’ group (N=218), twelve patients (5.5%) had no implant condition, 94.5%had peri-implant condition. In the non-smokers group (N=271), 14 patients (5.2%)had no implant condition, and 94.8% had the peri-implant condition (Figure 3.1.8).These proportional differences were not significant (Chi-square test, p=0.868).Systemic diseasesThe failure rate for patients with one or more reported systemic conditions was9.3%, while for the patients with potentially no systemic diseases, it was 9.8%(Figure 3.1.9), and this difference was not significant (Chi-square test, p=0.859).In regard to peri-implant condition, the majority of peri-implant conditionwere seen in patients with no reported systemic conditions (96.6%), whileperi-implant condition were seen in 94.3% of patients with one or more reportedmedical conditions (Figure 3.1.10). There were no significant differences in diseaserates between patients with and without any of the systemic diseases (Chi-squaretest, p=0.366).The only significant difference was related to patients having diabetes. Thefailure rate for diabetic patients was 17.6%, while for the non diabetic patientsdiabetes, it was 8% (Chi-square test, p=0.005). In regard to peri-implantcondition, 100% of diabetic patients experienced peri-implant condition and 93.8%of non diabetic experienced it (Chi-square test, p=0.031).Table 3.1.2 presents comparisons of implant failure rates between patients withand without specific systemic conditions.Table 3.1.3 presents comparisons of peri-implant condition between patients37Figure 3.1.7: Implant-related outcomes (implant failure) by smoking statusFigure 3.1.8: Implant-related outcomes (peri-implant condition) by smoking status38Figure 3.1.9: Implant-related outcomes (implant failure) by presence of medical condi-tionsFigure 3.1.10: Implant-related outcomes (peri-implant condition) by presence of medi-cal condition39Table 3.1.2: Patient-level analyses: Implant failures (primary outcome) according togeneral health conditionsMedical diseases Implant Failures (primary outcome)Removal N (%)a SignificancebCardio Yes (N=296) 25 (8.4) 0.437No (N=301) 31 (10.3)Diabetes Yes (N=85) 15 (17.6) 0.005No (N=512) 41 (8.0)Gastro Yes (N=161) 17 (10.6) 0.548No (N=436) 39 (8.9)Psychiatric Yes (N=102) 7 (6.9) 0.338No (N=495) 49 (9.9)Orthopedic Yes (N=250) 25 (10.0) 0.659No (N=347) 31 (8.9)a Percentage of valid totalb Chi-Square or Fischer’s Exact test (when conditions for Chi-Square not met)with and without specific systemic conditions.3.2 Implant-level analysis3.2.1 Univariate statisticsMissing dataFor the implant-level analysis, information about the implant type was missing for476 implants (31.9%), and information about implant length was missing for 45implants (3.0%) and for implant width for 60 implants (4.0%). The informationabout the torque of the implant and the quality of bone at the time of implantplacement was missing for 225 and 263 implants, respectively (15.1%, 17.6%).Numerous dental charts did not include complete implant-related periodontal40Table 3.1.3: Patient-level analyses: Peri-implant condition (secondary outcome) accord-ing to general health conditionsMedical DiseasesPeri-implant Condition (secondary outcome)No peri-implant condition With peri-implant condition SignificancebN (%)a N (%)aCardio Yes (N=248) 13 (5.2) 235 (94.8) 0.940No (N=241) 13 (5.4) 228 (94.6)Diabetes Yes (N=71) 0 (0.0) 71 (100.0) 0.031No (N=418) 26 (6.2) 392 (93.8)Gastro Yes (N=352) 4 (2.9) 133 (97.1) 0.140No (N=137) 22 (6.3) 330 (93.8)Psychiatric Yes (N=84) 5 (6.0) 79 (94.0) 0.775No (N=408) 21 (5.2) 384 (94.8)Orthopedic Yes (N=210) 10 (4.8) 200 (95.2) 0.635No (N=279) 16 (5.7) 263 (94.3)a Percentage calculated of a valid total percentage.b Chi-Square or Fischer’s Exact test (when conditions for Chi-Square not met).information either at the first examination or at the follow-up appointment.Theperiodontal information about pocket depth was missing in 332 of 1494 implants(22.2%), about recession-related status in 368 of 1494 cases (24.6%), bleeding onprobing was not charted for 734 of 1494 implants (49.1%).(Table 3.2.1).41Table 3.2.1: Implant-level univariate descriptive analysesVariables N (valid %)a Missing N (% of total)Implant siteMaxillary 790 (52.9) 0/1494 (0.0)Mandibular 704 (47.1)Implant locationAnterior 413 (27.6) 0/1494 (0.0)Posterior 1081 (72.4)Implant typeStraumann ITI 564 (37.8))476/1494 (31.9)Nobel Biocare 352 (23.6)Astra 102 (6.8)Implant widthNarrow 396 (27.6)60/1494 (4.0)Regular 637 (44.4)Wide 401 (28.0)Implant lengthShort 243 (16.8)45/1494 (3.0)Long 1081 (74.6)Very Long 125 (8.6)Torque at time of placementLow 410 (32.3)225/1494 (15.1)Medium 399 (31.4)High 460 (36.2)Bone qualitySoft 133 (10.8)263/1494 (17.6)Medium 776 (63.0)Dense 322 (26.2)Periodontal parametersPocket depth 1162 (77.8) 332/1494 (22.2)Recession 1126 (75.4) 368/1494 (24.6)Bleeding on probing 760 (50.9) 734/1494 (49.1)a Percentages calculated from valid data.42Figure 3.2.1: Implant distribution according to the archDescriptive statisticsOf the total implants included in this retrospective review, 47.1% were placed inthe maxilla, and 52.9% were placed in the mandible (Figure 3.2.1).The detailed distribution of the implants placed in maxilla is presented inFigure 3.2.2 and the distribution of mandibular implants in Figure 3.2.3.Figure 3.2.2: Distribution of implants placed in maxilla (by teeth)43Figure 3.2.3: Distribution of implants placed in mandible (by teeth)The majority of implants (72.4%) were placed in the posterior region, andaround one-third of them (27.6%) were placed in the anterior region (Figure 3.2.4).Figure 3.2.4: Implant distribution according to implant locationIn the graduate periodontics clinic, implants from three manufacturers wereused, namely Branemark/Nobel Biocare, ITI/Straumann and Dentsply Sirona. Ofall, 564 implants were Straumann implants, 352 were Nobel Biocare implants, and102 were Astra implants (Figure 3.2.5).44Figure 3.2.5: Implant distribution according to implant typeMost of the implants had a regular platform (44.4%), and the remaining 55.6%were equally distributed between the narrow and wide platform implant groups(Figure 3.2.6).Figure 3.2.6: Implant distribution according to implant widthRegarding the implant length: the majority of implants were long 74.6%,16.8% were short implants, and 8.6% were very long implants (Figure 3.2.7).Figure 3.2.7: Implant distribution according to implant length45At the time of the placement, 36.2% of implants were placed with high torque,31.4 % were placed with medium torque, and 32.3% were placed with low torque(Figure 3.2.8).Figure 3.2.8: Implant distribution according to torque at time of placementMore than half of the implants included in the study (63.0%) were placed inthe medium quality bone, 26.2% were placed in a dense bone, and 10.8% of theimplants were placed in soft bone (Figure 3.2.9).Figure 3.2.9: Implant distribution according to the quality of bone3.2.2 Bivariate analysesPrior to bivariate analyses, it was important to see if the length of follow-up timehas an effect on the study outcomes. The baseline follow-up was considered as thefirst follow-up after at least 1 year following implant placement.46Figure 3.2.10: Time of implant failure (months)No follow-up record was available in charts after implant placement for 320implants (21.4%). Most of the implants (33.0%) were followed up for a period of24-60 months after placement.Results of bivariate analyses comparing implants with various follow-upperiods are presented in Table 3.2.2. No significant follow-up related differenceswere found either in regards to implant failures or peri-implant condition(Chi-square test, p=0.311, p=0.108, respectively). Thus, for the subsequentanalyses, the data for all implants were combined, irrespective of the duration ofthe follow-up time (Table 3.2.3).The time of failure was varied. The range of failure time was between 0-121months. Of all, around 25% of failing implants failed within 12-20 months, half ofthem failed within 22-70 months and 25.0% of them failed within 71-121 months.(Figure 3.2.10).47Table 3.2.2: Implant-level analyses: Implant failures and peri-implant condition accord-ing to different follow-up periodsFollow-up period Implant failures Significanceb Peri-implant condition SignificancebN (%)a N (%)a0 - 23 months 14 (4.8) 217 (96.9)24 - 60 months 19 (3.9) 0.311 342 (94.7) 0.10861 - 120 months 10 (2.6) 264 (92.6)a Percentage calculated of a valid total percentage.b Chi-Square or Fischer’s Exact test (when conditions for Chi-Square not met).Table 3.2.3: Implant-level analyses: Implant failure rates according to differentimplant-related conditionsImplant-related characteristics Implant Failures SignificancebN (%)aArches Maxillary (N=790) 47 (5.9) 0.006Mandibular (N=704) 21 (3.0)Implant location Anterior (N=413) 21 (5.1) 0.541Posterior (N=1081) 47 (4.3)Implant typeStraumann (N=564) 28 (5.0)0.832Nobel (N=352) 15 (4.3)Astra (N=102) 4 (3.9)Implant widthNarrow (N=396) 16 (4.0)0.952Regular (N=637) 27 (4.2)Wide (N=401) 18 (4.5)Implant lengthShort (N=243) 5 (2.1)0.116Long (N=1081) 53 (4.9)Very Long (N=125) 4 (3.2)Torque at time of placementLow (N=410) 21 (5.1)0.639Medium (N=399) 15 (3.8)High (N=460) 20 (4.3)Bone qualitySoft (N=133) 6 (4.5)0.358Medium (N=776) 20 (2.6)Dense (N=322) 7 (2.2)a Percentage calculated of a valid total percentage.b Chi-Square or Fischer’s Exact test (when conditions for Chi-Square not met).48Arches of implant placementImplant failure rates were compared between the two arches. The implant failurerate was 5.9% in the maxilla (47 out of 790 implants) and 3.0% in the mandible (21out of 704 implants) (Figure 3.2.11). This difference was significant (Chi-squaretest, p=0.006).Figure 3.2.11: Implant failure by archSimilarly, peri-implant condition rates were compared between the two arches(Figure 3.2.12). Among maxillary implants, 92.7% had signs of peri-implantcondition. In the mandible, 94.4% of the implants had peri-implant condition.These proportional differences between maxillary and mandibular implants werenot significant (Chi-square test, p=0.269).49Figure 3.2.12: Peri-implant condition by archImplant locationImplant failure rates were compared between implants placed in the anteriorregions (incisor or canine sites) and implants placed in the posterior areas(premolar and molar sites). The implant failure rate for the anterior implants(n=21) was 5.1%, and for the posterior implants, it was 4.3% (n=47) (Figure3.2.13). This difference was not significant (Chi-square test, p=0.541).Implant condition rates were also compared between implants placed in theanterior and posterior regions of the jaw. Among anterior implants, 94.9% hadsigns of peri-implant condition, and 4.1% of the implants had no peri-implantcondition (Figure 3.2.14). In the posterior region, 93.0% of the implants hadperi-implant condition, and 7.0% of implants in this region were not associatedwith peri-implant condition. This difference in rates of peri-implant conditionbetween the two regions was not statistically significant (Chi-square test, p=0.248).50Figure 3.2.13: Implant failure by locationFigure 3.2.14: Peri-implant condition by location51Implant BrandThere was a non-significant (Chi-square test, p=0.832) difference in failure ratesamong different implant systems used at UBC, in slight favour of the Astra system(3.9%) (Figure 3.2.15).Figure 3.2.15: Implant failure comparison among 3 implant typesIn regards to the peri-implant condition, Straumann implants were the leastassociated with peri-implant condition (91.8%) than other types of implants.However, these differences in rates of the peri-implant condition among differentimplant systems were not statistically significant (Chi-square test, p=0.092).Implant widthWide implants had a 4.5% failure rate, regular platform implants had a 4.2%failure rate, and narrow implants had a 4.0% failure rate (Figure 3.2.17). These52Figure 3.2.16: Peri-implant condition comparison among 3 implant typesdifferences in failure rates were not significant (Chi-square test, p=0.952).In regards to the peri-implant condition, regular implants had the highest rateof peri-implant condition (95.0%), while both narrow and wide implants had verysimilar rates of condition (91.7% and 92.4%, respectively) as shown in Figure 3.2.18.The difference among these rates was not significant (Chi-square test, p=0.150).53Figure 3.2.17: Implant failure by implant widthFigure 3.2.18: Peri-implant condition by implant width54Implant lengthSimilar to the implant width, the difference in the length did not associatesignificantly with the implant failure rates (Chi-square test, p=0.116) (Figure3.2.19).Figure 3.2.19: Implant failure by implant lengthComparisons of peri-implant condition among different implant length groups(Figure 3.2.20) showed that the implant length did not have a significantrelationship with implant condition (Chi-square test, p=0.063).TorqueTorque was measured at the time of the implant placement. Implants placed at ahigh torque had a failure rate of 4.3% while the failure rate for the implants placedat a low torque was 5.1%, and for the implants placed at a medium torque, it was55Figure 3.2.20: Peri-implant condition by implant length3.8% (Figure 3.2.21). This difference was not significant (Chi-square test, p=0.639).Peri-implant condition rates were also compared in regard to the variation ofthe placement torque. Among implants placed at high torque, the majority (97.0%)had peri-implant condition(Figure 3.2.22). The condition rates among implantsplaced with different torque were not statistically significant. (Chi-square test, p=0.660).Bone qualityBone quality was measured at the surgical sites, and the failure rates among theimplants placed in different bone quality are compared in Figure 3.2.23. Implantsplaced in the dense bone had the lowest failure rate (2.2%) compared to the failurerates of implants placed in the soft (4.5%) or medium bone (2.6%). This difference56Figure 3.2.21: Implant failure by torque at time of placementFigure 3.2.22: Peri-implant condition by torque at time of placement57was not statistically significant (Chi-square test, p=0.358).Peri-implant condition rates were also compared in groups of implants placedin different bone quality. It was found that all implants placed in the soft bonewere associated with peri-implant condition (100%), while the implants placed inthe medium bone density had the lowest percentage of the condition (81.4%)(Figure 3.2.24). This bone quality-related difference was not significant (Chi-squaretest, p=0.162).58Figure 3.2.23: Implant failure by quality of boneFigure 3.2.24: Peri-implant condition by quality of bone594 DISCUSSIONThe present retrospective study evaluated outcomes of implant treatments providedwithin the period from January 1st, 2009, and December 31st, 2018, by the graduateperiodontic residents at the Dental Clinic of the University of British Columbia.The current study evaluated two treatment-related outcomes, namely: implantfailure as a primary outcome and peri-implant condition as a secondary outcome.The primary outcome can be indicative of ultimate failure or the endpoint of theimplant survival and relates to implants that were removed or needed to beremoved. Only a small subset of implants fell under this category. The secondaryoutcome referred to the condition that has an impact on or may eventually lead tothe primary outcome, i.e. peri-implant condition could lead to implant failures, ifleft untreated. Primary and secondary treatment-related outcomes presentedslightly different trends. As expected, the rates were lower for the primaryoutcome(4.6%)than for the secondary outcome (93.5%). Thus, studying thesecondary outcome is of clinical importance in providing us with a clearer pictureof the conditions of the implants before these implants may reach the level ofultimate failure. In the current study, the failure rate (primary outcome) ofimplants was 4.6%; this rate is lower than the failure rate reported in a similarprevious retrospective study where the outcomes of implant treatments placed in60an earlier time period in the same university setting were examined. The previousstudy that examined the time period between 1989-2006 reported an implantfailure rate of 7.7% [117].Another retrospective study evaluated dental implant failure rate in caseswhere surgery was performed by oral and maxillofacial residents. The study foundthat the overall failure rate of implants placed by oral and maxillofacial surgeryresidents was around 9.0%. [115].In the current study, the majority of the risk indicators examined did not havesignificant associations with the two study outcomes except for these risks:Diabetes(patient-level risk indicator), Maxillary arch (implant-level risk indicator). Weobserved that diabetes was associated with higher rates of both outcomes, namelyimplant failure and peri-implant condition (Chi-square test, p=0.005, p=0. 0.031,respectively). This result is in agreement with the Moy et al. 2005 retrospectivestudy, which found a relative risk of 2.8 for implant failure in diabetics (even if theyare well controlled) [16].Likewise, Fiorellini et al. concluded that the survival rate of dental implants incontrolled diabetic patients is lower than that documented for the generalpopulation, but there is still a reasonable success rate. The increase in failure rateoccurs during the first year following prosthetic loading [118]. There is compellingevidence that implants are as successful in controlled diabetics as they are innon-diabetic patients [68, 119, 120].Implant failure rates were also compared between the two arches. The implantfailure rate was 5.9% in the maxilla and 3.0% in the mandible (Chi-square test,p=0.006). Similarly, a study in 2015 [121] evaluated the survival of immediateimplants placed at maxillary and mandibular sites and found that maxillaryimplants (5.1%) had a higher failure rate than mandibular implants (2.7%).61Although we did not observe a significant association between higher failingrate and smoking, smoking had been reported to be associated with increasedimplant failures in earlier studies [49] [16, 31, 47]. Similar to our findings, a morerecent study[122] found that smoking was not significantly associated with implantfailure among the moderately rough surface implants, while it was associated withimplant failure among the group with minimally rough surface implants.This lackof association in our study could be because the implants in the current study weremodern, rough surface implants, which are usually associated with higher survivalrates [123]. It is possible that advances in implant surface topography contribute totheir higher survival rates to the point that the detrimental effect of smokingbecomes negligible [124].Our results are also similar to many other studies and reviews that have shownthat implants placed in patients with osteoporosis are similarly successful to thoseplaced in non-osteoporotic patients [119, 125]. Mombelli and Cionca’s 2006 reviewanalyzed data from 17 papers and found that the evidence for an associationbetween osteoporosis and implant failure was low [119].The current study has several limitations that could be listed as follows:• The data was collected via a retrospective review of patient charts. As withany retrospective study, there is a possibility of misreporting. Thus, theresults could be biased by poor documentation that may threaten the validityand reliability of the findings.• The present study did not evaluate the radiographic information. Thisinformation was not included mainly due to multiple operators takingradiographs, probably at different angles, consequently, the direct comparisonof radiographs might be not reliable.62• This study did not include information related to technical failures, such asimplant fracture, loss of supra-structures, abutment fracture, frameworkfractures, esthetic and phonetic complications, screw loosening, etc.• The presence of missing data. The prime concern with missing data waswhether the findings could be biased; undoubtedly, this is a major threat tothe study’s internal and external validity.• Limited external validity: findings of the present study are context-specific.Thus, not widely generalizable.635 SUGGESTIONS FOR FUTURESTUDIESIn order to acquire valid evidence in the future, a similar study can be repeated,but it needs to have a sample of patients preferentially with a similar length offollow-up and complete follow-up information. This means that information onwell-defined time periods should be reported for the entire cohort.Since this is a retrospective study of implants placed over a long time period,there was no standard protocol for charting during the follow-up visits. The beststudy design for the evidence is long-term prospective cohort study on dentalimplants.Clinical assessments should include periodontal pocket depths (PPD),recessions, bleeding on probings (BOP) and radiographs. Biological complicationsdefined by (1) the threshold level of PPD, (2) the presence/absence ofBOP/suppuration assessed at any examination interval and (3) crestal bone lossovertime must be described for implants and their neighbouring teeth.Future studies should include information about technical failures. Technicalcomplications could be divided into (1) major: such as implant fracture, loss ofsupra-structures, (2) medium: such as abutment or abutment fracture, framework64fractures, esthetic and phonetic complications and (3) minor: such as abutmentand screw loosening, loss of retention, and loss of screw hole sealing. The type andnumber of events of technical complications per time interval, as well as time/ costrequired, could also be reported.Another suggestion relates to diabetic patients is monitoring the level ofdiabetes control at the time of implant placement and throughout the wholefollow-up period, i.e. periodic assessment of glycosylated hemoglobin (HbA1c)levels.It is also suggested to compare losses that occur prior to loading and thosethat take place during the implant function. Survival and success (free of allcomplications) of the supra-structures should also be reported.Currently, the university protocol includes a radiographic follow-up every twoyears after the implant restoration. This protocol should be strictly enforced.656 CONCLUSIONSIn the clinical-educational setting, the implant treatment-related failure rate waslower than the failure rate reported in a retrospective study done in the samesetting in an earlier time period.The majority of the potential risk indicators we examined did not havesignificant associations with the two study outcomes we chose.For future studies to allow for the proper comparison among clinical cases, andmost importantly for the clinical patient monitoring, a standardized protocolincluding the guidelines for both clinical and radiographic assessments should bestrictly followed to enable recording of the necessary information for each case atthe time of implant planning, its placement, implant restoration and follow-upvisits.66References[1] Millennium Research G. U.S. markets for dental implants 2001: executivesummary. Implant Dent. 2001;10(4):234–7. Available from:https://www.ncbi.nlm.nih.gov/pubmed/11840994.[2] Stanford CM. 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