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Implant treatment outcomes at the University of British Columbia graduate periodontics clinic : a retrospective.. Lamberts, Bridget Evelyn 2009

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    IMPLANT TREATMENT OUTCOMES AT THE UNIVERSITY OF BRITISH COLUBIA GRADUATE PERIODONTICS CLINIC: A RETROSPECTIVE ANALYSIS    by  BRIDGET EVELYN LAMBERTS  B.Sc., The University of Western Ontario, 2003 D..S., The University of Toronto, 2007      A THESIS SUBMITED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE  in  THE FACULTY OF GRADUATE STUDIES  (Craniofacial Science)   THE UNIVERSITY OF BRITISH COLUMBIA  (Vancouver)      December 2009   © Bridget Evelyn Lamberts, 2009  ii ABSTRACT  Objectives: Dental implants have predictable outcomes and high survival rates. However, a smal but significant subset of patients experience implant failure. A retrospective review of charts at UBC was conducted to determine how patient-, disease-, site-, surgeon- and implant design-centered risk factors afect the survival of implants. Methods: A review of implants placed betwen 1989-2006 was completed. Inclusion criteria required a one-year post-placement diagnostic radiograph. Implant failure was defined as the loss or removal of an implant at any time. Bivariate analyses were used to identify variables asociated with implant failure. Risk factors with p-values < 0.05 or that were deemed clinicaly relevant by previous studies were included in stepwise linear multiple regresion and logistic regresion analyses. Results: Based on the inclusion criteria, 107 patients and 300 implants were included in the study. Follow-up ranged from 1.00 to 19.79 years (mean 4.08 + 2.95 years). At follow-up, 92.3% of implants survived and 84.1% of patients did not experience failure, In the failing implant group, 13.1% of patients had one failed implant and 2.8% of patients had two failed implants. The survival rate of replacement implants was 85.71%. Most factors studied had no statisticaly significant impact on survival. Only simultaneous sinus augmentation and removable prostheses were significantly asociated with failure and guided bone regeneration was significantly asociated with survival. In the regresion analyses, the predictors showing the largest efect on thread exposure were: implant model, jaw (in favor of mandibular implants), and surface (in favor of rough surfaces). The odds ratio for implant failure was 16.87 for osteotome sinus elevation and 0.288 for decreasing implant width.  iii Conclusions: The survival rate for implants placed at UBC is similar to those reported in the literature. Most variables considered risk factors did not have a statisticaly significant efect on implant failure. Given the high survival rates of implants, a smal sample size does not alow for trends in the data to reach statistical significance, even if a true diference exists.                           iv TABLE OF CONTENTS ABSTRACT....................................................................................................................ii TABLE OF CONTENTS..............................................................................................iv LIST OF TABLES........................................................................................................vi LIST OF IGURES.....................................................................................................vii 1. INTRODUCTION......................................................................................................1 2. REVIEW OF THE LITERATURE............................................................................2 2.1 Patient-centered risk factors...................................................................................................2 2.1.1 Age......................................................................................................................................................2 2.1.2 Gender.................................................................................................................................................4 2.1.3 Smoking status....................................................................................................................................5 2.2 Disease-centered risk factors..................................................................................................8 2.2.1 Osteoporosis.......................................................................................................................................9 2.2.2 Diabetes.............................................................................................................................................11 2.2.3 Periodontal disease...........................................................................................................................14 2.3 Implant design-centered risk factors...................................................................................17 2.3.1 Implant dimensions..........................................................................................................................17 2.3.2 Surface of Implant............................................................................................................................20 2.4 Implant site-centered risk factors........................................................................................22 2.4.1 Previous or simultaneous sinus augmentation................................................................................22 2.4.2 Previous or simultaneous guided bone regeneration......................................................................25 2.4.3 Location in the arch and bone density............................................................................................26 2.5 Level of training of the surgeon............................................................................................27 3. AIM..........................................................................................................................30 4. MATERIALS AND METHODS..............................................................................32 5. RESULTS.................................................................................................................36 5.1 Patient-level analysis..............................................................................................................37 5.1.1 Distribution of implants...................................................................................................................37 5.1.2 Implant follow up.............................................................................................................................38 5.1.3 Implant survival................................................................................................................................39 5.1.4 Demographic factors........................................................................................................................40 5.1.5 Smoking status..................................................................................................................................41 5.2 Implant level analysis.............................................................................................................43 5.2.1 Implant design..................................................................................................................................43 5.2.2 Previous periodontal disease............................................................................................................48 5.2.3 Pre- or peri-operative bone augmentation......................................................................................50 5.2.4 Asesment of implant site at time of fixture placement...............................................................54 5.2.5 Implant site.......................................................................................................................................56 5.2.6 Post-operative chemotherapy..........................................................................................................60 5.2.7 Post-operative complications...........................................................................................................61 5.2.8 Implant restoration...........................................................................................................................62 5.2.9 Level of training of the clinician.....................................................................................................66 5.2.10 Replacement implants....................................................................................................................69 5.2.11 Peri-implant bone los....................................................................................................................69  v 5.3 Regression analyses................................................................................................................72 6. DISCUSION..........................................................................................................75 6.1 Patient-level analysis..............................................................................................................75 6.1.1 Distribution of implants...................................................................................................................75 6.1.2 Implant folow up.........................................................................................................................76 6.1.3 Implant survival............................................................................................................................77 6.1.4 Demographic factors........................................................................................................................78 6.1.5 Smoking status..............................................................................................................................80 6.2 Implant level analysis.............................................................................................................81 6.2.1 Implant design..................................................................................................................................81 6.2.2 Previous periodontal disease............................................................................................................86 6.2.3 Pre- or peri-operative bone augmentation......................................................................................87 6.2.4 Asesment of the implant site at the time of fixture placement...................................................91 6.2.5 Implant site.......................................................................................................................................93 6.2.6 Post-operative chemotherapy..........................................................................................................94 6.2.7 Post operative complications...........................................................................................................95 6.2.8 Implant restoration...........................................................................................................................97 6.2.9 Level of training of the clinician.....................................................................................................99 6.2.10 Replacement implants..................................................................................................................100 6.2.11 Peri-implant bone los..................................................................................................................101 6.3 Regression analyses..............................................................................................................103 6.4 Study limitations...................................................................................................................104 6.5 Conclusions............................................................................................................................105 6.6 Future directions...................................................................................................................106 REFERENCES..........................................................................................................108 APPENDICES...........................................................................................................129 APPENDIX A: Periodontal charting.......................................................................................129 APPENDIX B: Surgical summary...........................................................................................130 APPENDIX C: Implant surgical summary............................................................................131 APPENDIX D: Post-operative sumary................................................................................132 APPENDIX E: Implant guarante form.................................................................................133 APPENDIX F: Variables included...........................................................................................134 APPENDIX G: Implant dimensions........................................................................................136 APPENDIX H: Radiographic signs of marginal bone loss around implants....................137 APPENDIX I. Documentation for future cases......................................................................139 APPENDIX J: Ethics course certificate..................................................................................141     vi LIST OF TABLES  Table 1. Reasons for case exclusion…………………………………………………….37 Table 2. Follow up time after implant therapy in years………………………………...38  Table 3. Post-operative chemotherapy – antibiotics…………………………………….60  Table 4. Post-operative chemotherapy – analgesics…………………………………….60 Table 5. Post-operative chemotherapy – other agents…………………………………..61 Table 6. Incidence of post-operative complications…………………………………….61 Table 7. Variables reaching or approaching statistical significance in logistic regresion analysis and the corresponding odds ratios……………………………………………..73   vii LIST OF FIGURES  Fig 1. The percentages of patients with one or more than one implant placed at the UBC graduate periodontics clinic……………………………………………………………..38 Fig 2. Percentage of patients experiencing one or more failed implants………………..39 Fig 3. Number of implants placed and number of failed implants in each age group…..40 Fig 4. Implant survival and failure in never, former and current smokers………………41  Fig 5. Implant survival and failure in never or former smokers compared to current smokers…………………………………………………………………………………..42 Fig 6. Number of implant failures related to model or brand of implant………………..43 Fig 7. The efect of surface roughnes on implant survival……………………………..45 Fig 8. Implant survival based on implant width…………………………………………46 Fig 9. Efect of implant length on implant survival……………………………………..47  Fig 10. Reason for tooth loss prior to implant placement……………………………….48  Fig 11. Implant survival related to the reason for tooth loss…………………………….49  Fig 12. The efect of guided bone regeneration (both prior to and simultaneously with implant placement) on implant survival…………………………………………………51 Fig 13. Efect of direct sinus augmentation prior to implant placement (lateral window  technique) on implant survival…………………………………………………………..52  Fig 14. Efect of simultaneous indirect sinus augmentation (osteotome technique) on  implant survival……………………..…………………………………………………..53  Fig 15. Efect of torque on implant survival……………………………………………..54  Fig 16. Survival of implants based on the jaw in which the implant was placed………..56  Fig 17. Implant survival related to the region of the jaw………………………………..57    vii Fig 18. Implant survival related to region of placement in the maxilary arch…………..58  Fig 19. Implant survival related to region of placement in the mandibular arch………..59  Fig 20. Distribution of diferent types of permanent restorations on implants…………..62  Fig 21. Efect of the type of permanent restoration on implant survival………………..63  Fig 22. Percentage of patients experiencing prosthodontic complications post-implant  placement and restoration………………………………………………………………..64  Fig 23. Percentage of patients experiencing prosthetic complications with fixed and   removable appliances…………………………………………………………………….65   Fig 24. Number of implants that survived and failed related to the level of training of the  clinician…………………………………………………………………………………..66  Fig 25. The percentage of implant failures placed by clinicians at diferent  training levels…………………………………………………………………………….67   Fig 26. Percentage of patients without implant failure based on the level of training of  their treating clinician……………………………………………………………………68  Fig 27. Number of threads exposed over time related to implant model………………..69  Fig 28. Number of threads exposed over time based on surface roughnes…………….71              1 1. INTRODUCTION  Implant therapy for partialy and completely edentulous patients has become a treatment mainstay in modern dentistry. During the 1970s, paralel studies by Branemark and Schroeder introduced the concept of osseointegrated implants (Romeo et al., 2002). The vast majority of clinical studies completed since that time, with at least 5-year follow up, clearly indicate the dental implants have predictable outcomes and high survival rates (Schou et al., 2004). Despite the reported succeses, a smal but significant subset of patients do experience implant failure (Moy et al., 2005). The identification of risk factors for implant failure is key to informed patient consent and education, treatment planning and improvements in implant design (Moy et al., 2005). The following report outlines numerous patient-, disease-, site- and implant design-centered factors that have been studied in terms of their impact on the succes of implant therapy. The efect of the level of training of the surgeon placing the implant fixture on implant survival is also discussed. A retrospective review of patient charts at the University of British Columbia graduate periodontics clinic was conducted to determine how such risk factors have afected the survival of implants placed in this educational seting.      2 2. REVIEW OF THE LITERATURE  2.1 Patient-centered risk factors 2.1.1 Age  Patient-centered factors are particularly interesting in how they relate to implant succes. One factor that has been long studied is the efect of increasing age on implant succes rates. As Brocard et al. (2000) explains, anatomic or histologic variations in diferent age groups may contribute to diferences in succes rates (Brocard et al., 2000). In particular, the loss of bone mineral with increasing age may acount for such diferences, especialy in women (Cuenin et al., 1997). Bone remodeling appears to be les eficient in older populations and older individuals are more likely to be completely edentulous which has been linked to lower succes with implant treatment (Brocard et al., 2000). Moy et al. (2005) published a retrospective cohort study based on data from 1,140 patients treated over 21 years by the same surgeon using various implant systems (Moy et al., 2005). They reported that advanced age doubled the risk for implant failure; patients older than 60 years of age were twice as likely to have adverse outcomes (Moy et al., 2005). Brocard et al. (2000) published a prospective, multicentre report on 1,022 ITI implants placed betwen 1991 and 1999 and followed for seven years (Brocard et al., 2000). Younger patient groups (<40 years and 40-60 years) had succes rates at or above the global mean succes rate for the study, while the succes rate for the older group (>60 years) was significantly lower (Brocard et al., 2000).  3 Four hundred and sixty-four patients with 1852 Branemark implants placed betwen 1979 and 1999 were followed for at least six months in Deluca and Zarb’s 2006 paper (DeLuca et al., 2006a). No diferences were found betwen age groups and it was concluded that age was an insignificant variable in early implant failures (DeLuca et al., 2006a). In a much smaler study by Dao et al. (1993) the highest implant failure rates were actualy reported in the youngest age group (Dao et al., 1993). In another smal cohort study, implants placed in geriatric patients had an overal 99% succes rate, which is comparable or beter to reported succes rates in the general population (Grant and Kraut, 2007). Lemerman and Lemerman (2005) published a retrospective study involving 1,003 implants of various designs placed betwen 1987 and 2002 and folowed until 2003 (Lemerman and Lemerman, 2005). Once again, he concluded that succes was unafected by patient age (Lemerman and Lemerman, 2005). Shirota et al. (1993) studied the efect of aging on osseointegration of implants in rats (Shirota et al., 1993). In the young rats, new trabecular bone formed around the implants, with rapid contact at the bone-implant interface (Shirota et al., 1993). In contrast, older rats demonstrated les bony growth and les bone to implant contact, suggesting that the rate and volume of bone formation around implants decreases with age (Shirota et al., 1993). A similar study also found that older rats had the lowest percent bone-to-implant contact, thicknes of bone contact and area of bone surrounding the implant (Takeshita et al., 1997). Clearly, evidence exists that age influences bone formation around dental implants. Whether this translates to lower succes rates for implant therapy sems controversial. Improvements in implant design, particularly in terms of surface  4 roughnes, sems to have improved succes of treatment to a degre that the efects of factors such as age are smal, or even negligible. Older age groups may include: a greater number medicaly compromised individuals (including those with osteoporosis, type I diabetes or head and neck iradiation), a larger proportion of patients with periodontitis or a history of the disease, and a higher number of patients with substantial loss of alveolar bone (potentialy requiring more complex surgical and prosthetic treatment plans). Age may simply be implicated due to its close asociation to these other factors that have the potential to increase implant failure. Older age should not be considered a contraindication for implant treatment. Patients should be aware that there is evidence of les eficient bone formation around implants but that the evidence that this leads to decreased implant succes rates is not strong. 2.1.2 Gender  The possible efect of patient gender on implant treatment outcomes has been extensively studied in the literature. A number of large studies with long-term folow-ups, as wel as numerous review papers have concluded that gender has no efect on implant succes (Blanes et al., 2007; Dao et al., 1993; DeLuca et al., 2006a; Lemerman and Lemerman, 2005; Levin et al., 2006; Mombeli and Cionca, 2006; Moy et al., 2005). One specific exception involves post-menopausal women who have been found to have lower succes rates, particularly in the maxilary arch (August et al., 2001; Moy et al., 2005). This is closely related to bone density and osteoporosis and wil be more thoroughly discussed in those sections of this review.  5 2.1.3 Smoking status   The detrimental efect of smoking on wound healing and periodontal disease has been wel established (Baig and Rajan, 2007). Smoking impedes the function of polymorphonuclear leukocytes and macrophages in a number of ways (Bain, 2003). It also contributes to low tisue oxygenation, causes systemic release of epinephrine and norepinephrine, decreases collagen deposition, increases platelet aggregation and blood viscosity, etc. (Moy et al., 2005). Long-term smokers also have lower bone mineral content than non-smokers (Has et al., 1996). Despite the documented efects of smoking on post-surgical healing, it wasn’t until 1992 that Jones and Triplet first asociated smoking with implant failure (Jones and Triplet, 1992).  A large retrospective evaluation of 2,194 Branemark implants by Bain and Moy found that smoking was the most significant risk factor for implant failure in their population (Bain and Moy, 1993). The overal failure rate in smokers was 11.3% compared to 4.76% in non-smokers (Bain and Moy, 1993). When poor bone quality was considered (posterior maxila), smokers experiences a 17.9% failure rate, in contrast to the 7.3% failure rate in non-smokers (Bain and Moy, 1993). A 1994 report by DeBryn and Collaert demonstrated similar results: a 9% failure rate in smokers versus a 1% failure rate in non-smokers (De Bruyn and Collaert, 1994). Baelum and Elegard studied periodontaly compromised patients and found that smokers were 2.6 times more likely to have explanted implants than non-smokers (Baelum and Elegard, 2004). Moy et al. (2005) conducted a retrospective cohort study of 1,140 patients over 21 years (Moy et al., 2005). They reported that smoking was a significant predictor of implant failure, with a relative risk of 1.56 (Moy et al., 2005). Studies and reviews that echo the findings of the  6 above authors are numerous (Aykent et al., 2007; DeLuca et al., 2006b; Hinode et al., 2006; Karoussis et al., 2003; Mombeli and Cionca, 2006; Olson et al., 2000a; Walace 2000; Widmark et al., 2001). Bain and Moy (1993) also found diferences betwen moderate and heavy smokers, suggesting a possible dose-dependent efect on implant failure (Bain and Moy, 1993). Lindquist et al. (1996) found greater marginal bone loss around implants in heavy smokers than those with low cigarete consumption (Lindquist et al., 1996). A majority of failures in smokers appear to occur after the second-stage surgery when implants are uncovered and can be adversely afected by toxic products in cigarete smoke, much like periodontal tisues are afected (Baig and Rajan, 2007; DeLuca et al., 2006a). Gorman et al. (1994) and Lambert et al. (2000) found the majority of failures occurred within the first year, but after the implants were exposed (Gorman et al., 1994; Lambert et al., 2000). It sems that smoking is not asociated with an inability to atain osseointegration but rather, an inability to maintain it (DeLuca et al., 2006a). It has also been shown that smoking has a greater efect on maxilary implants than mandibular implants, which is likely related to the poor bone quality asociated with the maxilary arch (Baig and Rajan, 2007; Has et al., 1996). In contrast, numerous more recent reports have found no significant diferences betwen smokers and non-smokers in terms of implant survival (Bain 2002; Blanes et al., 2007; Brocard et al., 2000; Kumar et al., 2002; Levin et al., 2007; Peleg et al., 2006a; Schwartz-Arad et al., 2002; Schwartz-Arad et al., 2008). It has been argued that roughened surfaces may increase implant succes rates to a point where the efect of smoking is negated (Kumar et al., 2002). They speculate that smoking simply does not  7 play a significant role in osseointegration and survival when surface-modified implants are used (Kumar et al., 2002). This view has been highly contested and the evidence from both sides is compeling. In fact, Hinode et al. (2006) questioned the results of Bain et al.’s 2002 meta-analysis (Bain 2002; Hinode et al., 2006). The 2002 review found no significant diferences betwen implant succes rates in smokers and non-smokers but Hinode claims that if the data is evaluated using a synthesized odds ratio a significant risk of implant failure exists for smokers (OR=2.17) (Hinode et al., 2006). Even if advances in implant design can negate efects of smoking on implant failure, it appears as though smokers continue to experience more complications associated with their treatment. Smoking has been found to adversely afect the health of peri-implant tisue (Aykent et al., 2007; Has et al., 1996). Peri-implant pocket depth, bleding indices and bone levels were found to be significantly worse in smokers than non-smokers, particularly in the maxila (Aykent et al., 2007; Has et al., 1996). The incidence of peri-implantitis is also elevated in smokers (Baig and Rajan, 2007; Heitz-Mayfield and Lang, 2004). Lindquist et al. (1997) reported increased marginal bone loss around implants in smokers (Lindquist et al., 1997). Deluca et al. (2006) confirmed these findings and Blanes et al. (2007) found a similar trend, although the diference betwen smokers and non-smokers was not statisticaly significant (Blanes et al., 2007; DeLuca et al., 2006b). It has been shown that the risk of implant failure or complications can be reduced to that of a non-smoker if the habit is ceased (Lambert et al., 2000). In 1996, Bain published results indicating that if patients are placed on a smoking cesation protocol one wek prior to implant placement, the implant succes rates are not significantly  8 diferent from non-smokers (Bain 1996). Deluca et al. (2006) found that the efect of smoking on wound healing could be reversed with a 1-2 wek smoke-fre pre-surgical period (DeLuca et al., 2006a). Smoking should not be considered an absolute contraindication for treatment (DeLuca et al., 2006b; Moy et al., 2005). The evidence supporting altered wound healing in smokers is dificult to ignore but whether or not this translates to increased implant failure rates is les clear. Smokers should be advised of the possible increased risk for implant failure and complications and a smoking cesation protocol should be recommended prior to fixture placement. 2.2 Disease-centered risk factors  Systemic disease   The efect of systemic pathology on implant osseointegration and maintenance is of particular interest to clinicians who would benefit from the ability to acurately predict a patient’s individual risk. The evidence appears varied: it has been reported that healthy patients have higher implant succes rates than those with systemic disease (Brocard et al., 2000), while others publish opposing conclusions (Moy et al., 2005). It can be agred that controlled systemic disease should not be considered a contraindication for treatment (Brocard et al., 2000). For the purposes of this review, we wil concentrate on two of the most extensively researched conditions: diabetes and osteoporosis.   9 2.2.1 Osteoporosis   Osteoporosis is defined as a bone mineral density level of 2.5 standard deviations or more below the mean of a young population (Beikler and Flemig, 2003). Thre main types of primary osteoporosis exist: post-menopausal, age-related and idiopathic (Mombeli et al., 2006). Secondary osteoporosis can be caused by a variety of factors (diabetes, alcoholism, COPD, anticonvulsant drugs, etc.) (Beikler and Flemig, 2003). It is asumed that the decrease in bone density asociated with osteoporosis afects the mandible and maxila as it does other bones (Humphries 1989), but this remains unconfirmed in the literature (Beikler and Flemig, 2003). It is also asumed that impaired bone metabolism asociated with osteoporosis may afect osseointegration of implants (Beikler and Flemig, 2003). Trabecular bone is much more afected by such metabolic changes than cortical bone, making areas such as the posterior maxila more likely to be severely afected by the disease (Beikler and Flemig, 2003). However, osteoporotic fractures usualy heal readily, suggesting that the repair proces in these patients likely remains adequate for implant integration (Dao et al., 1993). This remodeling proces does not appear to difer from that sen in healthy patients, as demonstrated by numerous histologic studies of implants retrieved from osteoporotic jaws (de Melo et al., 2008; Shibli et al., 2008a; Shibli et al., 2008b). These studies showed bone-to-implant contact and bone maturity comparable to that found in healthy subjects (de Melo et al., 2008; Shibli et al., 2008a; Shibli et al., 2008b). In osteoporotic rabbits, bone formation was delayed, trabecular volume and mineral apposition reduced, but considerable bony contact occurred with time (Lugero et al., 2000; Mori et al., 1997).  10  Clinical studies have delivered conflicting results. Many reports, like Friberg et al. (2001) have shown succes rates in osteoporotic women comparable to healthy populations (Friberg et al., 2001; Mombeli et al., 2006). Evidence also exists that implants are highly succesful in patients with osteoporosis induced by corticosteroids or other endocrinopathies (Cranin et al., 1991; Friberg 1994; Steiner and Ramp, 1990). Others have found reduced succes rates in osteoporotic patients. Blomqvist (1998) found that there was a significantly reduced succes rate following maxilary sinus augmentation and implant placement in patients with reduced bone mas density as compared with age- and sex-matched control patients (Blomqvist 1998). August et al. (2001) found that there was in increased failure rate for implants placed in the maxila in postmenopausal women without estrogen supplementation compared to pre-menopausal women (August et al., 2001). Moy et al. (2005) describes that in severe cases of osteoporosis it may be dificult to obtain good primary implant stability due to a decrease in trabecular bone mas (Moy et al., 2005). It is advisable that the amount of implant surface area available for osseointegration should be maximized in these patients (rough surfaces, wide platform, etc.) (Moy et al., 2005). Osteoporosis does not rule out implant placement, but the diference in bone metabolism and possible increased failure risk should be explained to afected patients. Careful asesment of nutrition and systemic health should be completed, and calcium and vitamin D supplementation ensured in the pre-operative period (Beikler and Flemig, 2003). Patients should be advised to quit smoking, since it is an important risk factor for osteoporosis (Beikler and Flemig, 2003). Where there is insufficient bone for  11 implant placement, augmentation should be considered prior to placement (Beikler and Flemig, 2003). The surgeon can also consider extending the healing period before loading, and using implant designs that ensure optimal bone-implant contact (Beikler and Flemig, 2003). 2.2.2 Diabetes   Diabetes can be clasified into two types. Type I diabetes is an autoimune disease afecting the beta cels of the pancreas, leading to insufficient insulin production (Mombeli et al., 2006). Type I diabetes is the most common form in the adult population and is asociated with obesity (Kahn and Flier, 2000). It is sen as a resistance to insulin and an inability to produce compensatory insulin (Mombeli et al., 2006). Systemic complications are varied and can include: retinopathy, nephropathy, neuropathy, micro and macro-vascular disease, and altered wound healing (Beikler and Flemig, 2003). In terms of oral health - xerostomia, periodontitis and caries have been linked to this disease (Mombeli et al., 2006). Microvascular disease of the gingival tisue may compromise blood supply and contribute to delayed wound healing and an elevated risk for infection (Shernof et al., 1994). Many aspects of wound healing are profoundly afected by tisue hyperglycemia, including neutrophils and leukocyte function, chemotaxis and phagocytosis (Goodson and Hunt, 1986).  In Shernof et al’s 1994 study and Olson’s 5-year follow up of 89 type I diabetes undergoing implant therapy, the survival rate for fixture and prosthesis was approximately 90% (Shernof et al., 1994). They concluded that the percentage of diabetic patients experiencing failures semed relatively high, but the percentage fel within normal range for published studies on healthy patients (Olson et al., 2000b;  12 Shernoff et al., 1994). They also found that fasting plasma glucose, HbA1c values and smoking history were not statisticaly significant predictors of implant failure (Olson et al., 2000b; Shernoff et al., 1994). Mombeli et al. reviewed six studies, which included diabetic patients in their study population (Mombeli et al., 2006). He found there was no unequivocal tendency towards higher failure rates in diabetics (Mombeli et al., 2006). However, the largest reviewed study was Moy’s 2005 21-year retrospective cohort publication, which included 48 diabetic patients (Moy et al., 2005) They found a statisticaly significant increase in the relative risk for implant failure in diabetics (R=2.75) (Moy et al., 2005). Their results demonstrated that even wel controlled diabetics were at greater risk for implant failure compared to healthy controls (succes rate of 68.75% vs. 93.46%) (Moy et al., 2005). In a beter designed but smaler study (n=15 diabetic patients), patients were matched to two control subjects in terms of age, gender, location of implants, duration of edentulism, type of prosthesis, etc. (Acursi, 1973). No increased risk of implant failure or prosthodontic complications were found in diabetic patients compared to their matched controls (Acursi, 1973). In a retrospective review of 215 implants in 40 diabetic patients, Fiorelini et al. found that the survival rate of dental implants in controlled diabetics is lower than that of the general population, but the results are reasonable (Fiorelini et al., 2000). Of the studies that found an increase in implant failure, it was generaly asociated with uncovering of implants and the early phase of loading (Beikler and Flemig, 2003). Such failures may be atributed to a diminished imune response and reduced bone turnover due to microvascular disease (Olson et al., 2000b).  13  Studies involving diabetic animal models have shown that bone-to-implant contact is significantly reduced with this disease (Fiorelini et al., 1999; Nevins et al., 1998). Bone density was also found to be slightly lower around implants in diabetic patients, but was comparable to controls in insulin-controlled animals (Nevins et al., 1998). It appears as though the healing proces is impaired in uncontrolled diabetic animals but osseointegration can stil occur. Good initial contact sems to optimize this proces and areas with abundant cortical bone appear les afected (McCracken et al., 2000). The biological pathways through which diabetes may afect osseointegration is presently poorly described in the literature (Beikler and Flemig, 2003).  Beikler and Flemig outlines some special considerations for diabetic patients undergoing implant therapy in his 2003 review as follows: a) ensure optimal glycemic control in the pre- and post-operative periods, b) the practitioner should be experienced in managing possible peri- and post-operative complications (ex: hypoglycemic crisis during surgery), c) antibiotic therapy should be prescribed, with the first dose given pre-operatively, and d) chlorhexidine use is recommended peri- and post-operatively (Beikler and Flemig, 2003).  The evidence for patients with diabetes to experience higher implant failure rates is equivocal at present (Mombeli et al., 2006). Animal studies have shown that osseointegration is impaired in subjects with poor glycemic control (Beikler and Flemig, 2003). Patients should be aware of the current evidence on this topic and precautions should be taken to ensure their disease is wel controlled and their risk of post-operative infection is as low as possible.  14 2.2.3 Periodontal disease   A variety of studies support the theory that existing periodontal pockets around teth can act as reservoirs for periodontal pathogens that can rapidly colonize tisues around implants (Leonhardt et al., 1993; Papaioannou et al., 1996; Sbordone et al., 1999). It sems reasonable to asume that a patient who is periodontitis-susceptible and who does not receive proper treatment can experience a similar risk for atachment loss at implants and teth (Hardt et al., 2002). In fact, it has been shown that one year after implant placement, overal periodontal conditions were correlated with the conditions of the tisues around implants (Brägger et al., 1997). Implants harboring Actinobacilus actinomycetemcommitans, Prevotela intermedia or Porphymonas gingivalis had deeper probing depths and more severe signs of inflamation than implants fre of such pathogens (Karoussis et al., 2003). Currently there are a number of review papers that thoroughly discuss implant therapy in periodontaly susceptible patients, including: Van der Weijden et al. (2005), Karoussis et al. (2007) and Schou et al. (2008) (Karoussis et al., 2007; Schou et al., 2004; Van der Weijden et al., 2005). There exist two clinical studies that examine implant therapy in healthy patients and those with periodontitis in terms of implant survival and incidence of biological complications. The Karoussis et al. (2003) publication included treated periodontitis patients and healthy controls (Karoussis et al., 2003). In the periodontitis group, the teth being replaced by dental implants were lost due to periodontal disease (Karoussis et al., 2003). In the healthy group, teth were lost due to other reasons (caries, fractures, trauma, etc.) (Karoussis et al., 2003). Patients were offered supportive therapy every 3-6 months and were recruited for a clinical and  15 radiographic examination 10 years after implant placement (Karoussis et al., 2003). Implants replacing teth lost due to chronic periodontitis had lower survival rates than those lost due to other reasons (90.5% vs. 96.5%) (Karoussis et al., 2003). This higher susceptibility for implant loss became evident only after 6 years of service (Karoussis et al., 2003). Based on their definition of peri-implantitis (PD >5mm and BOP+), 28.6% of implants in the periodontitis group and 5.8% of implants in the healthy group experienced such complications (Karoussis et al., 2003). Based on their succes criteria (PD <5mm, BOP -and bone loss <0.2mm annualy), succes rates of 52.4% and 79.1% of implants replacing teth lost due to periodontitis and for implants replacing teth lost due to other reasons, were reported (Karoussis et al., 2003). The authors theorize that, based on the long time period before failure and the high incidence of peri-implantitis, eventualy loss may be due to repeated episodes of peri-implantitis over several years (Karoussis et al., 2003).  In a retrospective study by Hardt et al. (2002), patients were divided into groups acording to their age-related bone loss score (ArB-score) (Hardt et al., 2002). This score is calculated by dividing the percentage bone loss by the patient’s age multiplied by the number of teth remaining (Hardt et al., 2002). The two extreme quartiles of the population were considered either the periodontitis group (upper quartile) or the non-periodontitis group (lower-quartile) (Hardt et al., 2002). Once again, implant failure rates were higher in the periodontitis group (8.0% vs. 3.3%) (Hardt et al., 2002). In addition, there was also a statisticaly significant relationship betwen the ArB-score and peri-implant bone level change from abutment connection to 5 years later (Hardt et al., 2002).  16  Other studies have reported similar results. Brocard et al. (2000) found that periodontaly maintained patients had significantly lower succes rates compared to the global succes rate (a diference of 9%) (Brocard et al., 2000). Short-term results in periodontitis patients appear to be very high, with drops in succes during the 5-10 year period (Schou et al., 2004). Similarly, the occurrence of peri-implantitis sems to increase as the duration of the study increases (Schou et al., 2004). A study by Polizi et al. (2000) examining the placement of implants into extraction sockets found that the succes of the implant over 5 years was unafected by the reason for tooth loss (Polizi et al., 2000). In contrast, Grunder et al. (1999) found more implant failures when periodontitis was cited as the reason for tooth loss (Grunder et al., 1999). Novaes et al. (2003) studied bone-to-implant contact in periodontal infected sites in dogs (Novaes et al., 2003). They found that osseointegration of the implants was not diferent in sites with induced periodontitis compared to healthy sites (Novaes et al., 2003). This may be another indication that increased failures are not related to healing, but perhaps to infection of the peri-implant tisues over time (Karoussis et al., 2007). Most recently, Safi et al. (2009) completed a systematic review and meta-analysis on the risk of implant failure and marginal bone loss around implants in patients with a history of periodontal disease (Safi et al., 2009). They concluded that the odds ratio for implant survival was significantly in favor of periodontaly healthy patients (OR=3.02) and implants placed in those with periodontitis experienced more peri-implant bone loss than those without a history of periodontitis (standard mean diference =0.61mm) (Safi et al., 2009). Al acepted studies (n=5) showed more favorable implant survival in those without history of periodontitis, but none showed that the diference was  17 statisticaly significant (Safi et al., 2009). Four of the included studies found there was more marginal loss around implants in those with a history of the disease and two of these found that the diference was significant (Safi et al., 2009). They concluded that there is currently a “moderate” level of evidence to indicate that periodontitis subjects are more susceptible to implant failure and marginal bone loss (Safi et al., 2009). Oral implants may be succesfully placed and maintained in patients with a history of periodontal disease (Karoussis et al., 2003; Schou et al., 2004). Although these studies report lower succes rates in those with periodontitis compared to healthy patients, the succes rates lie within an aceptable range for the general population (>90%) and the diferences are often not statisticaly significant (Karoussis et al., 2007; Schou et al., 2004). However, patients with a history of periodontitis should be aware that lower survival and succes rates, as wel as higher incidences of peri-implantitis and peri-implant bone loss have been reported in this population (Karoussis et al., 2003; Schou et al., 2004; Van der Weijden et al., 2005). Since complications and implant loss are likely related to periodontal pathogens, treatment of periodontal disease and continued maintenance are esential to ensure healthy periodontal and peri-implant tisues (Van der Weijden et al., 2005). It is also important to consider that smoking may be a significant confounder is not always reported in these studies (Van der Weijden et al., 2005). 2.3 Implant design-centered risk factors 2.3.1 Implant dimensions   In posterior areas, where the height of alveolar bone above the inferior alveolar nerve canal (mandible) or below the maxilary sinus (maxila) is often limited, the use of “short” (<10 m) dental implants is a significant clinical benefit. This limits the need for  18 extensive bone augmentation or sinus lifting, pre-surgical tomography, (Morand and Irinakis, 2007) reduces surgical risk, discomfort, time and overal cost of treatment (Misch et al., 2006; Montes et al., 2007; Morand and Irinakis, 2007). Short preparations pose les risk to overheating of bone and are useful when smal interarch distance or angled/dilacerated roots are present (Misch et al., 2006). When machined implants were commonly used, clinicians sought to place the longest possible implant to maximize the surface area for osseointegration (Morand and Irinakis, 2007). The advent of “rough” surfaces on implants has led to significantly beter long-term results and the diference in surface area compared to machined surface can help compensate for les length in the implant fixture (Morand and Irinakis, 2007).  Misch et al. (2006) reviewed the literature from 1991-2003 to examine failure rates asociated with implants <10 m in length (Misch et al., 2006). The average succes reported in the literature at this time was 85.3%, representing 2,837 implants (Misch et al., 2006). Failures of short implants generaly occurred after prosthetic loading and surgical succes did not vary with implant length (Misch et al., 2006). In his own 2006 retrospective evaluation of 745 implants, he found that implant length was not a factor in survival or succes over 6 years. He considered splinted implants with no cantilever load, mutualy protected or canine-guided occlusion and implant design that optimizes bone-implant contact as factors for succes with short implants (Misch et al., 2006).  A number of other studies were examined for this review, with mixed results. DeLuca et al. (1999) folowed 1852 Branemark implants placed over 20 years and concluded that a significantly greater number of early failures occurred in implants <10  19 m compared to longer implants (>10 m) (DeLuca et al., 2006a). A 3-year prospective report by Grunder et al. (1999) found that 80% of 7 m long implants failed (Grunder et al., 1999). Lekholm et al. (1999) studied 461 Branemark implants over 10 years and reported that shorter standard-diameter implants were lost significantly more often than longer ones (Lekholm et al., 1999). Al of the above studies used machined-surface implants. Romeo et al. (2004) studied 250 patients with a variety of implant-supported prosthesis (single-tooth prostheses, cantilever prostheses, fixed partial dentures or removable partial dentures) for 3.85 years (Romeo et al., 2004). Implant failure was not significantly influenced by implant length or diameter (Romeo et al., 2004). A retrospective evaluation of 1,387 single tooth implants over 6 years by Levin et al. (2006) found that implant survival was not related to implant dimensions (Levin et al., 2006). Blanes et al. (2007) completed a 10-year review of 192 posterior implants and concluded that length did not influence implant survival or peri-implant bone loss (Blanes et al., 2007). A multicentre report on 1,022 ITI implants followed over 7 years by Brocard et al. (2000) divided implants into groups acording to their length and found no diference in survival betwen groups (Brocard et al., 2000). It appears as though reports which include more rough surface implants, found that length did not influence succes while publications involving machined surfaces did find that shorter implants fared worse than their longer counterparts (Misch et al., 2006; Morand and Irinakis, 2007). In terms of biomechanics, osteointegrated bone-implant interfaces distribute most prosthetic load to the crestal portion of the implant body, with litle stres transfered to the apical portion (Misch et al., 2006). This may indicate that implant length is not a  20 primary factor in load distribution (Misch et al., 2006). To compensate for shorter length, a surgeon may consider a wide-diameter implant (ex: 5 m) (Morand et al., 2007). A 5 m wide x 6 m long implant has the same surface areas as a 3.75 m wide x 10 m long implant (Morand and Irinakis, 2007). In fact, width appears to be a more critical factor than length in terms of stres distribution (Petrie and Wiliams, 2005). Increasing implant diameter results in a 3.5-fold reduction in crestal strain, whereas increasing length leads to a 1.65-fold reduction (Petrie and Wiliams, 2005). Reports of increased failures with short implants may be due to: increased crown height (which acts as a vertical cantilever), excesive bite forces, and/or poor bone density (since they are most often placed in posterior regions) (Misch et al., 2006). To compensate for such risks, cantilevers should be avoided, occlusion adjusted to avoid any lateral movement, implants splinted and implant surface chosen to optimize osseointegration (Misch et al., 2006). Reduced mesio-distal dimension of the prosthesis and flatening of the cuspal inclines can also contribute to a more favorable load distribution (Morand and Irinakis, 2007). Morand and Irinakis (2007) suggest using a 2-stage approach with short implants, avoiding fre-end situations without a second implant for splinting, and compensating with wider diameter implants to increase succes rates, particularly in areas of poorer bone quality (Morand and Irinakis, 2007). 2.3.2 Surface of Implant   The quality of the implant surface influences wound healing at the implantation site and, in turn, osseointegration of the implant (Sykaras et al., 2000). Roughened surfaces demonstrate a number of advantages over machined surfaces, including: increased area for bone-implant contact to offer increased mechanical stability at  21 insertion, retention of the blood clot after placement, and stimulation of the wound healing proces (Morand and Irinakis, 2007). Plasma spray coating is a common way to alter the surface microtexture of implants (Sykaras et al., 2000). It can be used to apply titanium or hydroxyapatite (HA) onto metalic cores (Sykaras et al., 2000). Blasting with particles of varying sizes to create pits and depresions is another method of altering an implant’s surface; aluminum oxide or titanium oxide are commonly used (Sykaras et al., 2000). Chemical (acid) etching to erode the surface of an implant has also been used to alter surface topography (Sykaras et al., 2000). Some companies have used a combination of the above methods to achieve an optimal surface texture. For example, Struamann’s SLA surface uses a combination of sandblasting with large grit particles and acid etching with hydrochloric-sulfuric acid (Sykaras et al., 2000). At present, al methods are commonly used, with the exception of the HA-coated implants, which have been asociated with high rates of peri-implant infections and low long-term succes rates (Aykent et al., 2007). Smal micropits present on roughened surfaces may influence biologic pathways at the bone-implant interface since the pits are similar in size to cels and large molecules (Kasemo and Lausma, 1994). Larger micropits likely serve a mechanical function in stres transfer (Kasemo and Lausma, 1994). Roughened surfaces have actualy been reported to increase the atachment of osteoblasts and gingival cels onto the implant (Sykaras et al., 2000). Studies on the efect of surface roughnes on the ability of osteoblasts to produce a mineralizing matrix found that machined, titanium oxide grit-blasted, and plasma-sprayed titanium surfaces displayed unique paterns of matrix  22 formation, demonstrating that a surface-dependent physicochemical and biochemical conditioning of implant surfaces takes place (Cooper et al., 1999). The increase in surface area may be the most valuable factor of altered surface topographies, since the opportunity for osseointegration at the bone-implant interface is greatly increased. Such an increase in area may compensate for the use of shorter or narow diameter implants in areas where conventional implants are impossible to place (Morand and Irinakis, 2007).  Numerous experimental studies, including Bernard et al. (2003) confirmed that textured implants have increased bone contact and beter fixation measured by torque removal (Aykent et al., 2007; Bernard et al., 2003; Carlson et al., 1988; Feighan et al., 1995; Sykaras et al., 2000). In a human histologic study, machined and grit-blasted microimplants were placed in 27 patients (Ivanoff et al., 2001). Blasted implants had 37% bone-to-implant contact after six months, compared to 9% contact on the machined implants (Ivanoff et al., 2001). The findings in clinical studies appear to concur, with significantly higher succes rates with rough implants compared to those with machined surfaces (Bain 2002; Hinode et al., 2006; Misch et al., 2006).  The advances in surface topography has revolutionized the field of dental implantology and, as previously mentioned, may decrease or negate the efects of many of the patient and disease-centered risk factors discussed. 2.4 Implant site-centered risk factors 2.4.1 Previous or simultaneous sinus augmentation   As previously mentioned, implant placement in the posterior maxila has unique chalenges and limitations. Resorption of the alveolar proces, pneumatization of the  23 maxilary sinuses, and poor bone quality can complicate implant therapy (Sorní et al., 2005). Techniques proposed to overcome these limitations include: bone grafting, placement of implants in anatomical abutments and, most commonly, grafting the floor of the maxilary sinus (Sorní et al., 2005). This technique was first published by Boyne and James in 1980 and has been widely used and modified since it alows for the placement of implants of conventional length in grafted sinuses (Walace and Froum, 2003). Numerous studies have confirmed high succes rates for implants placed after sinus elevation and the topic can be best explored through systemic reviews by Walace and Froum (2003), Sorni et al. (2006), Esposito et al. (2008) and Aghaloo and Moy (2008), just to name a few (Aghaloo and Moy, 2007; Esposito et al., 2006; Sorní et al., 2005; Walace and Froum, 2003). This augmentation procedure has been wel documented and the long-term succes/survival (>5 years) of implants placed compares favorably to rates reported for implants placed in ungrafted areas of the maxila.  Walace and Froum’s meta-regresion analysis of 43 studies found that survival of implants placed in augmented sinuses ranged from 61.7% to 100%, with an average survival of 91.8% (Walace and Froum, 2003). Sorni et al. reported near identical figures in terms of survival rates (Sorní et al., 2005). Walace and Froum, among others, found that rough surface implants had higher survival rates than machined-surface implants in grafted sinuses (95.2% vs. 82.4%) (Del Fabbro et al., 2004; Del Fabbro et al., 2008a; Pjeturson et al., 2008; Walace and Froum, 2003). Implants survived beter when particulate grafts were (92.3%) used instead of block grafts (83.3%) and grafts were more succesful when resorbable membranes were placed over lateral windows (100% with a barier membrane, 92.6% without) (Walace and Froum, 2003).  24  Contrary to what was previously thought, the use of autogenous bone in sinus grafting does not appear to improve implant and graft survival (Walace and Froum, 2003). A study by Halman et al. actualy found higher survival rates in sinuses grafted with a xenograft (Bio-Os®, Osteohealth) compared than those grafted with autogenous bone or a 20/80 xenograft/autograft mix (Halman et al., 2002). Aghaloo et al. (2007) reviewed 5,128 implants and also reported higher succes with Bio-Os® vs. autogenous bone (95.6% vs. 92.0%). In a recent Cochrane review by Esposito et al. (2008), it was also suggested that bone substitutes such as Bio-Os® should replace autogenous bone for sinus lift procedures (Esposito et al., 2008). That said, it appears as though Pjeturson et al. (2008) was the first systematic review to examine the efect of diferent bone materials for implants with rough surfaces (Pjeturson et al., 2008). Historicaly, machined implants have been used much more often in combination with autogenous bone, while rough surface implants have been used with bone substitutes (Del Fabbro et al., 2008a). When the type of graft used was considered only for rough implants al grafting materials showed similar annual failure rates (1.13% for bone substitutes, 1.1% for combination and 1.27% for autogenous) (Pjeturson et al., 2008).  Imediately placed implants appear to compare favorably to those placed in a delayed fashion, with survival rates of 89.7% and 89.6%, respectively (Walace and Froum, 2003). This may be because they require more native bone to be present for placement and likely have good primary stability (Del Fabbro et al., 2008a). Poorest results correspond to cases where machined surface implants are used, initial alveolar crest heights are smal (<3 m) and block grafts are used (Pjeturson et al., 2008; Sorní et al., 2005; Walace and Froum, 2003).  25  A number of studies have reported that smoking is detrimental to the survival of implants in grafted sinuses (Peleg et al., 2006b). Kan et al. (1999) reported implant succes rates 17.4% lower in smokers compared to non-smokers (Kan et al., 1999). Olson reported a similar discrepancy betwen smokers and non-smokers in his 2002 study with implant failure rates of 12.7% in smokers compared to 4.8% of non-smokers (Olson et al., 2000a). Peleg et al. (2006) conducted a study on 2,132 implants simultaneously placed in grafted maxilary sinuses. Despite the fact that smokers also had significantly les alveolar ridge height than non-smokers, there was no statisticaly significant diference in the succes rates betwen the two groups (Peleg et al., 2006a). The high succes rates found in both smokers and non-smokers was atributed to the use of long, microtextured implants which alow for increased surface area for osseointegration, and that patients were asked to abstain from smoking for 10 days after the surgery (Peleg et al., 2006a). 2.4.2 Previous or simultaneous guided bone regeneration   Guided bone regeneration is based on the concept that, by applying a barier membrane, bone neogenesis could be induced on top of a flat bone surface, into a created wound space (Christensen et al., 2003). GBR enables the clinician to augment the width of deficient alveolar ridges, cover fenestrations or dehishences around implants, and alow imediate placement of implants in osseous defects or large extraction sites (Simion et al., 2001). The concept of GBR has been extensively studied and reviewed. Al review articles and clinical studies considered for this review agre that implant succes/survival in regenerated bone is comparable to succes/survival rates in native bone (Aghaloo and Moy, 2007; Blanco et al., 2005; Brocard et al., 2000; Christensen et  26 al., 2003; De Boever and De Boever, 2005; Esposito et al., 2006; Fiorelini. 2003; Fugazotto, 2005; Halman et al., 2002; Juodzbalys et al., 2007; Simion et al., 2001). A variety of materials have been used and studied including autogenous bone, xenograft materials, etc. A discussion of the diferent materials and their advantages and disadvantages is beyond the scope of this review. 2.4.3 Location in the arch and bone density   Many studies suggest that implants have higher survival and succes rates in the mandible than the maxila, particularly when the mandible is compared to the posterior maxila (Turkyilmaz and McGlumphy, 2008). This is largely atributed to the diferences in bone density betwen the mandible and maxila and betwen anterior and posterior sites (Turkyilmaz and McGlumphy, 2008). Lekholm and Zarb proposed a bone quality clasification (scale of 1 to 4) in 1985, which was based on a subjective asesment by the clinician (Lekholm and Zarb, 1985). The reproducibility and objectivity of this index has since been questioned (Turkyilmaz and McGlumphy, 2008). Computerized tomography (CT) may be the most objective and reliable method to analyze bone; Hounsfield unites determined by the software program can give an estimation of bone density (D1 bone, >1250 HU; D2 bone, 850-1250 HU; D3 bone, 350-850 HU; D4 bone, 150-350 HU, D5 bone , >150 HU) (Turkyilmaz and McGlumphy, 2008).  Based on CT imaging, the bone density recordings for the diferent regions of the jaws were: anterior mandible – 846 + 234 HU, posterior mandible – 526 + 107 HU, anterior maxila - 591 + 176 HU, posterior maxila - 403 + 95 HU (Turkyilmaz and McGlumphy, 2008). These are comparable to what has been reported in other publications (Norton and Gamble, 2001; Shapurian et al., 2006). In the Tukyilmaz and  27 McGlumphy (2008) study, bone density measures were correlated to insertion torque, and both were asociated with improved implant survival (Turkyilmaz and McGlumphy 2008).  Many studies concluded that implants placed in areas of increased bone density had beter succes and survival rates; mandibular implants fared beter than maxilary implants and anterior implants fared beter than posterior fixtures (DeLuca et al., 2006a; Grunder et al., 1999; Hinode et al., 2006; Lekholm et al., 1999; Moy et al., 2005; Polizi et al., 2000; Romeo et al., 2002). That said, with the advent of rough surface implants, survival rates appear to have improved to the point where the diferences in implant survival in the diferent regions are quite smal and not statisticaly significant (Aykent et al., 2007; Ferigno et al., 2002; Kumar et al., 2002; Morand and Irinakis, 2007; Romeo et al., 2004).  The concept of bone density may be most important when discussing the degre of primary stability available and deciding on the timing of implant loading and the type of prosthesis and occlusion (Misch et al., 2006). In general, it sems appropriate to maximize the surface area for osseointegration by choosing rough-surface implants with the largest dimensions possible given the amount of bone present and the prosthetic plan (Morand and Irinakis, 2007). This is likely most important in areas where bone density is sub-optimal, like the posterior maxila, and where there is some evidence of lower implant survival and succes rates (Morand and Irinakis, 2007). 2.5 Level of training of the surgeon   Litle has been published regarding the clinical outcomes of implant therapy in relation to surgical experience of the clinician. Increasingly, dental implants are being  28 placed by general practitioners with varying levels of surgical experience and implant training.  The first paper to evaluate the efect of surgical experience on early implant failures was a prospective study by Lambert et al. (1997). 2641 implants placed in 30 centers were followed (Lambert et al., 1997). Implants placed by inexperienced surgeons (those having placed les than 50 implants) failed twice as often as those placed by experienced surgeons (those having placed more than 50 implants) (Lambert et al., 1997). The greatest diference was found in the first nine cases, with later cases failing significantly les often (Lambert et al., 1997). In the first nine cases, the failure rate for inexperienced surgeons was 5.9%, compared to 2.4% for those with more experience (Lambert et al., 1997). They concluded that there is a definite learning curve asociated with the placement of dental implants (Lambert et al., 1997).  DeLuca et al. (2006) folowed 464 patients with 1852 implants over a 20-year period and found that surgical skil proved important in terms of implant succes (DeLuca et al., 2006a). They did not include information on the clinician’s experience but found that, if groups acording to early implant failure rates, surgeons in the high failure rate group (>8% failures) had a 2.71 times greater failure rate than those in the low failure group (<8% failures) (DeLuca et al., 2006a). Walton’s 2001 overdenture study found that inexperienced surgeons were more likely to place implants diverged from each other in the frontal plane and with a facial or lingual inclination (Walton et al., 2001). Conversely, Kohavi et al. (2004) published a retrospective study on 93 implant patients treated in a university training program (Kohavi et al., 2004). They concluded  29 that clinical experience was not an influencing variable on implant survival over 36 months (Kohavi et al., 2004). This may be partly explained by the surgical and prosthodontic collaboration betwen faculty and trainees that likely takes place in such a training program (Melo et al., 2006). Melo et al. (2006) studied implant survival rates in an oral and maxilofacial surgery program (Melo et al., 2006). One hundred and seventy-eight implants were placed in 56 patients by residents in diferent levels of training (Melo et al., 2006). There was no significant diference in implant survival rates when level of training was considered (Melo et al., 2006). In fact, implant survival rates were highest in the first two years of training compared to the third and fourth years (Melo et al., 2006). This likely reflects the level of complexity of cases given to residents as they progres through the program (Melo et al., 2006).  Infection, surgical trauma, impaired healing and premature loading are common causes of early implant failure and it is conceivable that these may be more common with les experienced clinicians (Melo et al., 2006). The evidence regarding clinician experience appears equivocal. Basic surgical principles should always be considered and extensive implant training is advised, particularly before complex treatment plans are executed (Melo et al., 2006). In general, it appears as though good outcome are achievable by surgeons in training (Melo et al., 2006).   30 3. AIM  The aim of the present study was to investigate implant survival rates and predictors for implant failure in a university teaching facility. A university seting enabled a comparison of the survivability of diferent implant systems under reasonably standardized conditions (charting systems, follow-up protocol, etc.). In addition, investigations of the clinical outcomes of implants placed in training programs is of great interest in view of other reports stating that prior surgical experience may be significant to implant survival (Kohavi et al., 2004). Such an investigation wil also provide an invaluable database of information for the graduate periodontology program. It may enable identification of areas where case documentation can be improved or treatment planning modified. This study wil also serve as a basis for addition of new cases and expansion of the study in the future.  The following hypotheses were tested: i) Implant survival at the UBC periodontology clinic is lower than that reported in randomized control trials, cohort and case studies in the published literature due to the clinician’s inexperience. ii) A history of smoking and periodontal disease negatively afects implant treatment outcomes. iii) Patient age, gender and history of systemic disease (diabetes or osteoporosis) do not have a significant impact on implant survival.  31 iv) Implants placed in the mandibular arch have beter survival rates than those placed in the maxilary arch and those placed in the anterior of either jaw fare beter than those placed in the posterior. v) Previous or simultaneous bone augmentation, the clinician’s asesment of bone quality at the time of surgery, implant model, taper, width, length and connection type do not significantly impact implant survival. vi) Rough surface implants survive beter and have les marginal bone loss than smooth surface implants. vii) Implants placed by inexperienced surgeons fail more often than those placed by more experienced clinicians in a training program.  32 4. MATERIALS AND METHODS   A retrospective chart review of patients treated in the University of British Columbia Graduate Periodontics program betwen January 1, 1989 and December 31, 2006 was conducted. The sample cohort had heterogeneous risk factors and the  inclusion criteria were as follows: 1) patients had one or more dental implant(s) placed by a resident or staf member of the graduate periodontics program; 2) records of a radiographic and clinical follow up visit at least one year post-implant placement were available; 3) the implant threads were clearly discernable in the radiographs taken at implant placement and follow up. Exclusion criteria included incomplete or unavailable patients records.  Implants from two manufacturers were used in this study (Branemark/Nobel Biocare, Yorba Linda, CA; and ITI/Straumann, Waldernburg, Switzerland). Throughout the study period, patient demographic data, surgical and follow up information was collected through standardized examination forms (health history questionnaire, periodontal charting, surgical summary sheet, implant surgery form, post-operative summary sheet, implant failure guarante form) as sen in appendices A-E. At follow up appointments, implant osseointegration was evaluated radiographicaly and clinicaly through various criteria, including: absence of signs or symptoms of pain, infection, neuropathy, mobility and absence of a peri-implant radiolucency. Study variables to be evaluated as risk factors for implant failure included: demographic (age, gender, medical status, smoking status), anatomic (bone quantity, bone quality, implant site), reconstructive (previous or simultaneous guided bone regeneration, previous or simultaneous sinus augmentation, types of materials used for  33 augmentation procedures), implant-specific (brand, model, surface, length, width), prosthodontic (type of provisional and permanent restorations, prosthodontic complications), peri-operative chemotherapy (type, dose and frequency of antibiotics, analgesics, steroids and chlorhexidine), surgical (level of training of the clinician, post-operative complications) and timing (imediate, early and delayed placement and loading) variables. Patients were clasified as current, former or never smokers based on what was reported on their health questionnaire and/or the implant screning form. For a complete list of data collected, refer to appendix F. The same data was also collected for any implant placed after an implant failure (replacement implants).   Demographic, clinical, surgical and follow up data was entered into a computer database (Microsoft Excel 2004; Microsoft Corporation, Redmond, WA). As in several other retrospective investigations (Del Fabbro et al., 2008a; Hämerle et al., 2002; Melo et al., 2006; Woo et al., 2004), our first outcome variable was implant failure, as in removal or exfoliation of an implant for any reason. Survival time was the duration of time (in months) from placement to removal or the date of the most recent follow up for implants that had not been removed. The second outcome variable was implant thread exposure over time (marginal bone loss), which was analyzed by subtracting the number of threads exposed at the time of implant placement by the number of threads exposed at the time of the most recent follow up.  Most published reports on implant succes use several criteria to determine succes vs. failure which include: no mobility of the implant, no peri-implant radiolucency on radiographic examination, les than 0.1-0.2 m of annual radiographic bone loss after the first year, absence of signs and symptoms such as pain, infection,  34 neuropathies or paresthesia, etc. (Albrektson et al., 1986; Albrektson and Zarb, 1993; Kohavi et al., 2004; Misch et al., 2008). The use of succes as an outcome variable was not possible due to the limited follow up data available. The follow up exams at UBC do not routinely consist of removal of any fixed splinted implant-supported restorations, and hence, do not alow for a true asesment of the mobility of each individual implant. Only radiographs in which implant threads are visible were considered in the present study. However, since the radiographs were taken by diferent clinicians using diferent radiographic equipment (digital radiography replaced film at UBC in 2006) and no stents were used, acurate comparisons betwen radiographs taken at placement at follow up were not possible. Also, due to the poor angulation of many radiographs, the lack of standardization in the radiographic methodology, and the many diferent models of implants used, an acurate calculation in milimeters of bone loss was also dificult. Any post-operative complications were asesed using only the chart notes, as patients were not re-examined for this study. Many of theses chalenges are typical of a retrospective study. Due to the limitations of this design, it would be inappropriate to make conclusions regarding implant “succes”.  Descriptive statistics were used for al study variables. Survival rates were calculated at both the implant and patient level. Bivariate analyses were used to identify risk factors asociated with implant survival. Risk factors with p-values < 0.05 or predictors that were deemed clinicaly relevant or important based on previous implant studies were included in logistic regresion analysis and in a stepwise linear multiple regresion analysis. The outcome variables for these analyses were: implant failure and threads exposed over time. Multicolinearity was tested and the tolerance values of the  35 predictors were asesed. Tolerance is an estimate of the colinearity of predictors, or how closely two predictors are related to one another (Peat and Barton, 2005). A tolerance value approaching zero indicates colinearity; the predictor shares its efects with other predictors (Peat and Barton, 2005). A tolerance value of one means that the efect of the tested predictor is completely unrelated with the other independent predictors (Miles, 2001). All statistical analysis was completed using the SPS program (SPS Inc, Chicago, IL, version 17.0).                 36 5. RESULTS  One-hundred and eighty-six patient charts were available for review in the current UBC chart filing system and the charting archives for patients who are no longer actively being sen at the university. Radiographs taken prior to July 1, 2006 were in a film format and found in the patient charts. Al radiographs taken after this date were in a digital format and examined using the Romexis software system (Planmeca Oy; Helsinki, Finland). Seventy-nine of the available charts had incomplete records and were not included in the study. The large majority of these charts did not a have a radiograph taken at the implant follow up appointment, or if it was taken, the radiograph was not considered diagnostic (implant threads were not visible due to poor angulation) (n= 64). Fourty-thre of these charts were part of a previous overdenture study where it appears as though the folow up protocol involved a clinical exam without radiographs. Since the inclusion criteria requires a diagnostic follow up radiograph at least one-year after implant placement, these charts were excluded. One patient chart had no radiograph from the time of implant placement (the baseline record to measure peri-implant bone loss) and six charts had no radiographs at al. Six charts had no surgical records and two patients had implants placed by surgeons not part of the graduate periodontology program. Al of these charts were excluded from the study (Table 1).       37 Table 1. Reasons for case exclusion Reason for exclusion Number of charts Lack of diagnostic follow up radiograph 64 Lack of radiograph at the time of placement 1 Lack of radiographs 6 Lack of surgical records 6 Implants placed by surgeons not afiliated with the graduate periodontics clinic 2 Total 79  5.1 Patient-level analysis 5.1.1 Distribution of implants  107 patients with 300 implants were included in the present review. Implants were placed betwen 1989 and 2006 in the UBC graduate periodontics clinic. The majority of patients had more than one implant placed, with a large proportion of patients with two implants, often in the lower mandible. 19.6% of patients had one implant placed, 48.6% of patients had two implants placed, while 31.8% of patients had thre or more implants placed (Fig 1).   38 Fig 1. The percentages of patients with one or more than one implant placed at the UBC graduate periodontics clinic. 5.1.2 Implant folow up  Table 2. Follow up time after implant therapy in years.   Minimum (years) Maximum (years) Mean + Std Dev (years) Time betwen stage 1 surgery and folow up 1.00 19.79 4.08 + 2.95 Time betwen restoration and follow up 0.51 18.77 3.46 +3.17  The mean follow up period ranged from 1.00 to 19.79 years. The mean time (+ SD) betwen implant placement and the most recent implant follow-up examination was 4.08 (+ 2.95) years. The mean time betwen the placement of the restoration and the most  39 recent implant follow-up exam was 3.46 (+ 3.17) years. This folow up period ranged from 0.51 to 18.77 years (Table 2). 5.1.3 Implant survival   Fig 2. Percentages of patients experiencing one or more failed implants. 84.1% of patients did not experience implant failure, 13.1% of patients had one failed implant and 2.8% of patients had two failed implants. No patients had more than two failed implants (Fig 2).  40 5.1.4 Demographic factors  Age  Fig 3. Number of implants placed and number of failed implants in each age group. Patients in the study ranged in age from 23.53 to 90.48 years, with a mean age (+ SD) of 59.04 (+ 11.61) years at the time of implant placement. Patients were categorized into thre age groups: under 40 years, 40-60 years and more than 60 years of age. 8.91% of patients were under 40 years of age, 37.62% of patients were betwen 40 and 59 years and 53.46% of patients were over 60 years of age. The percentages of patients in each age group with no implant failures were 77.78%, 78.95% and 88.89% respectively (Fig 3). There was no significant diference in survival rates betwen the diferent age groups (p=0.376).  41 Gender  Of the 107 included patients, 52 were males and 55 were females. 88.89% of female patients and 80.39% of male patients had no implant failures. There was no statisticaly significant gender diference in survival of implants (p=0.282). Systemic disease  The presence of systemic disease also had no efect on implant survival (p=0.230). Similarly, when some systemic diseases were examined individualy, there was no statisticaly significant efect of the diferent diseases on implant failure (diabetes p=0.253; osteoporosis p=0.606). 5.1.5 Smoking status  Fig 4. Implant survival and failure in never, former and current smokers.  42 Fig 5. Implant survival and failure in never or former smokers compared to current smokers. 73.1% of patients had never smoked, 13.5% were former smokers and 13.5% of patients were currently smoking at the time of implant placement. There was no statisticaly significant diference in implant survival betwen the smoking groups (p=0.454). However, there was a trend for current smokers to have more implant failures than never or former smokers (Fig 4). Eleven out of 76 never smokers experienced implant failure, while 2/14 former smokers and 3/14 current smokers lost implants. Even when the never and former groups were combined (to increase the sample size), there was no statisticaly significant diference betwen never/former smokers and current smokers (p=0.368) (Fig 5).   43 5.2 Implant level analysis  At the implant level, 92.3% of implants survived to follow up. 7.7% of implants failed over the mean 4.08 + 2.95 years follow up time. On average, implants failed after 44.22 + 46.32 weks. The minimum time from implant placement to failure or removal was two weks, and the maximum time from placement to failure was 209.29 weks. 5.2.1 Implant design  Implant brand  Fig 6. Number of implant failures related to model or brand of implant. Of the 300 implants included, 244 were Branemark or Nobel Biocare implants and 50 were Straumann implants. 22 of the Nobel implants failed (90.98% survived),  44 while one of the Straumann implants was lost (98.0% survived) (Fig 6). There was no statisticaly significant diference betwen survival rates of these two systems (p=0.070). Al of the Straumann implants were rough surface implants, while 33.06% of the Branemark/Nobel implants placed were smooth surface implants, which may explain the trend for Straumann implants to have fewer failures. However, when rough and smooth surface Branemark/Nobel implants were compared, there was no significant diference in implant survival percentages – 9.71% vs. 10.47% respectively (p=0.519). Of the implants included in the study, the earliest Straumann implant was placed in 2002, while Branemark/Nobel implants have been placed since 1997. Since Straumann implants are a relatively new addition to the grad perio program, these implants have shorter follow ups.            45 Implant surface  Fig 7. The efect of surface roughnes on implant survival. The efect of surface roughnes was compared for both implant systems and no significant diference in implant survival was sen betwen rough and smooth surface implants (p=0.362) (Fig 7). The survival rate for machined surface implants (n=99) was 90.9% and the rate for rough surfaced implants (n= 101) was 92.8%.         46 Implant dimensions - width  Fig 8. Implant survival based on implant width. Implants were grouped acording to width: narow (<3.9 m, n=119), regular (4.0 – 4.9 m, n=156) and wide (>5 m, n=25) platforms (appendix G, fig. 30). Wide implants had a 4.0% failure rate, regular platform implants had a 5.1% failure rate and narow implants had an 11.8% failure rate (Fig 8). The diferences betwen these failure rates were not significant (p=0.095).       47 Implant dimensions – length Fig 9. Efect of implant length on implant survival. Implants were also grouped acording to length: short (<10 m, n=37) and long (>10 m, n=263) (appendix G, fig. 31 and 32). 12.33% of the implants were short and 87.67% were considered long. The survival rate was 94.6% for short implants and 92.0% for long ones (Fig 9). Survival was not significantly diferent betwen groups (p=0.441).        If 10 m implants were considered as “short”, 42.0% of implants included were long, while 58.0% were short. The survival rate for long implants was 92.0%, and the same rate was 92.9% for short implants. Similar to the above, length did not have a significant efect on implant survival (p=0.476).     48 Other design features   Whether the implant was straight or tapered had no efect on implant survival (p=0.259). The type of connection (external vs. internal hex) also did not afect implant survival (p=0.334). 5.2.2 Previous periodontal disease  The efect of a deep probing depth or furcation involvement adjacent to an implant site was also examined. Those with adjacent probing depths of >3 m (n= 29) and/or an adjacent tooth with a Hamp clas I (n=15) or I (n= 9) furcation involvement did not have significantly more implant failures (p=0.612, p= 0.917).   Fig 10. Reason for tooth loss prior to implant placement.  49 Tooth loss was categorized into thre groups: tooth loss due to periodontal disease, tooth loss due to reasons other than periodontal disease, and tooth loss due to unknown reasons. Those specified as “unknown” had no clear indication in the patient’s chart as to why the tooth/teth was/were lost or the patient’s presented as edentulous and did not report why the teth were lost. Caries, tooth fracture, congenitaly mising teth, retained deciduous teth, trauma and persistent endodontic problems were considered “non-periodontal” reasons for tooth loss and acounted for 36.0% of tooth loss (n=36). Periodontitis acounted for 17.0% of tooth loss (n=17) and 47.0% of loss was for unknown or uncharted reasons (n=47) (Fig 10).  Fig 11. Implant survival related to the reason for tooth loss prior to implant placement.  50 Although the percentage failure for implants replacing teth lost due to periodontitis was higher than the percentage failure of implants replacing teth lost due to other reasons, this diference did not reach statistical significance (p=0.127) (Fig 11). Even when the group who lost teth for unknown or uncharted reasons were excluded, there was stil no significant efect of tooth loss for periodontal reasons on implant failure (p=0.462). 5.2.3 Pre- or peri-operative bone augmentation  Socket preservation  The efect of bone augmentation prior to or at the time of implant placement on implant survival was determined. Fiften socket preservation cases were included in the study, with one reported failure. Socket preservation had no significant efect on implant survival/failure (p=-0.678).                       51 Pre- or peri-operative guided bone regeneration    Fig 12. The efect of guided bone regeneration (both prior to and simultaneously with implant placement) on implant survival.  Guided bone regeneration (GBR) was completed prior to implant placement in 53 cases (17.67%), with only one reported failure (survival = 98.1%) (Fig 12). GBR had a nearly significant positive efect on implant survival (p=0.091). GBR was completed concurrently with implant placement in 18 cases (6.0%), with no implant failures. The efect of simultaneous GBR on implant survival was not significant (p=0.377). When both GBR procedures were combined, it appears as though bone augmentation has a significantly positive efect on implant survival (p=0.021, n= 71). This is likely because the larger sample size alows for the trend to reach statistical significance.     52 Pre- or peri-operative sinus augmentation     Fig 13. Efect of sinus augmentation prior to implant placement (lateral window technique) on implant survival.   Similarly, the efect of sinus augmentation prior to or simultaneously with implant placement on implant survival was investigated. Nine cases with lateral window sinus lifts prior to implant placement were included, with no implant failures. Sinus augmentation prior to implant placement did not have a statisticaly significant efect on implant survival (p=0.477) (Fig 13).  53   Fig 14. Efect of simultaneous (osteotome technique) sinus augmentation on implant survival. Osteotome sinus lifts, completed using a modified Summer’s technique (Summers 1994), in conjunction with implant placement were completed in 19 included cases, with five implant failures (a 26.3% failure rate) (Fig 14). Simultaneous sinus lifts were significantly asociated with implant failures (p=0.010).  54 When the analyses of both types of sinus augmentation were combined, there was stil a significant asociation with implant failure (p=0.05). 5.2.4 Asesment of implant site at time of fixture placement  Primary stability   Fig 15. Efect of torque on implant survival.  The relationship betwen implant survival and the amount of torque at implant insertion was studied. The mean insertion torque for implants that survived to the most recent follow up was 32.19 + 9.75 N⋅cm. The mean insertion torque (+ SD) for failed implants was 36.67 (+ 4.08) N⋅cm (Fig 15). Lower torque was significantly asociated with implant survival (p=0.049) (95%CI: -8.937; -.0.018).    55 Subjective assesment of the implant site   The standardized charting for implant placement includes a section to record the clinician’s impresion of the amount of bone resorption at the implant site, the vascularity and quality of the bone, as wel as the degre of primary stability of the implant. Each of these criteria is subjectively graded on a scale of 1 to 4; one being the most resorption, least vascular, poorest quality and poorest primary stability. The clinicians clasified 70.57% of cases as having moderate bone resorption, 50.69% of cases had good bone quality, 76.22% were rated as having good bone vascularity and 76.74% were deemed to have excelent primary stability. None of the above variables were significantly related to implant survival or failure (p=0.851, p=0.299, p=0.453 and p=0.481 respectively).               56 5.2.5 Implant site  Jaw   Fig 16. Survival of implants based on the jaw in which the implant was placed. Implant survival in the maxila was compared to survival in the mandible. The implant failure rate was 6.15% in the maxila (n=130) and 8.82% in the mandible (n=170) (Fig 16). This diference was not significant (p=0.262).         57 Region of the jaw  Fig 17. Implant survival related to the region of the jaw in which the implant was placed. Similarly, implant survival and failure rates were compared for implants placed in the anterior regions of the jaw (canine or incisor sites) and implants placed in posterior areas (premolar and molar sites). The implant failure rate for anterior implants (n=164) was 8.54%. The implant failure rate for posterior implants was 6.62% (n=136) (Fig 17). This diference was not significant (p=0.345).     58  Fig 18. Implant survival related to region of placement in the maxilary arch. The implant failure rate for the anterior maxila was 5.26% while the failure rate for implants placed in the posterior maxila was 6.85% (Fig 18). This diference was not significant (p=0.503).   59 Fig 19. Implant survival related to region of placement in the mandibular arch. The implant failure rate for implants placed in the anterior mandible was 10.28%, while the failure rate for those in the posterior mandible was 6.35% (Fig 19). The diference was not significant (p=0.282).         60 5.2.6 Post-operative chemotherapy  Table 3. Post-operative chemotherapy - antibiotics Antibiotic % of cases for which it was prescribed Amoxicilin 73.4% Doxycycline 3.1% Clindamycin 7.1% Amoxicilin and Metronidazole 0.7% Other 5.8% None prescribed 9.9%  Table 4. Post-operative chemotherapy - analgesics Analgesic % of cases for which it was prescribed or recommended Ibuprofen 59.4% Tylenol #3 24.8% Acetaminophen 7.7% Any over the counter analgesic 2.8% Toradol 3.1% Ketorolac 0.7% Other 1.5%      61 Table 5. Post-operative chemotherapy – other agents Other % of cases for which it was prescribed or recommended Chlorhexidine 75.3% Salt water rinses 5.3% Dexamethasone 26.7%    Post-operative prescription medications or recommended non-prescription medications were given out at the discretion of each resident or clinician and the supervising instructor. The above tables show the percentages of patients prescribed each agent. 5.2.7 Post-operative complications  Table 6. Incidence of post-operative complications. Post operative complication Incidence Bleding 1.9% Infection 5.7% Temporary paresthesia 0.67% Permanent paresthesia 0.67% No complications 91.06%  Table 6 lists the incidences of post-operative bleding (for which the patient was sen at the clinic after surgery), infection (for which the patient was prescribed antibiotics after the initial course of post-operative antibiotics), temporary and permanent paresthesia (as reported by the patient post-operatively). A single case of paresthesia was  62 deemed “permanent” since the patient reported paresthesia imediately post-operatively and at every subsequent recal examination. 5.2.8 Implant restoration  Distribution of implant supported restorations   Fig 20. Distribution of diferent types of permanent restorations on implants.  In this study, 39.0% of implants were restored with removable overdentures (n= 117), 29.0% were restored with splinted crowns (n=89), 15% with single crowns (n= 44), 10% with fixed partial dentures (n= 29) and 7% with fixed hybrid overdentures (n= 21) (Fig 20).    63  Fig 21. Efect of the type of permanent restoration on implant survival. The survival rate was 89.81% for implants restored with removable overdentures and 98.79% for implants restored with fixed restorations (Fig 21). Removable implant restorations were significantly asociated with implant failure (p=0.001) compared to fixed restorations (fixed ful-arch hybrid dentures, splinted crowns or single crowns).         64 Prosthodontic maintenance of implant-supported restorations    Fig 22. Percentage of patients experiencing prosthodontic complications post-implant placement and restoration. 68.3% of patients experienced one or more prosthodontic complications after implant placement and restoration (Fig 22). These included: esthetic problems, loosening of the abutment, isues with occlusion requiring laboratory work to adjust or re-make the prosthesis, a deficient margin that requires replacement of the restoration, fractured denture, denture retention isues, broken bars, etc. In terms of post-implant surgical procedures, 9.2% of implants had connective tisue grafting around the implant after placement.  65  Fig 23. Percentage of patients experiencing prosthetic complications with fixed and removable appliances. Of the 68.3% of patients with reported prosthetic complications, 49.7% were asociated with removable overdenture restorations and 18.7% were asociated with fixed implant restorations (Fig 23).         66 5.2.9 Level of training of the clinician  Fig 24. Number of implants that survived and failed related to the level of training of the clinician.         67    Fig 25. The percentage of implant failures placed by clinicians at diferent training levels.         68  Fig 26. Percentage of patients without implant failure based on the level of training of their treating clinician. We also investigated if the level of training of the clinician (ie. the year of the program of the clinician at the time of implant placement) impacted the survivability of the implants. Of the patients treated by clinicians in their first year of training (n= 17), 94.12% did not experience implant failure. Among those patients treated by surgeons in their second year of training (n= 40), 88.54% did not experience implant failure. 97.62% of patients treated by third year residents had al of their implants survive to follow up  (21 patients were treated by third year residents). 93.18% of patients treated by staf members (n= 22) had no implant failures (Fig 24-26). These diferences were not statisticaly diferent. (p=0.525).  69 5.2.10 Replacement implants  Fourten implants placed after an implant failure at that site (acounting for 63.4% of failures) had an adequate follow up period to be considered for this study. The survival rate of these implants were 85.71%. 5.2.11 Peri-implant bone loss   Fig 27. Number of threads exposed over time related to implant model. The number of threads exposed over time was used as a measure of peri-implant bone loss. Horizontal bone loss around the implants was a common finding and the number of threads without surrounding bone was asesed for each implant using the  70 follow up radiograph. The number of threads exposed at the time of implant placement was subtracted from the number of threads exposed at the most recent follow up. The diference, threads exposed over time, was used as the second outcome measure for stepwise linear multiple regresion analysis. 43.56% of Branemark/Nobel implants (n= 88) and 85.11% (n= 40) of Straumann implants had no progresion of exposed threads at follow up. Of the Straumann implants, 8.51% had one exposed thread (n= 4), 4.26% had two exposed threads (n= 2) and 2.13% (n= 1) had thre exposed threads (appendix H, Fig. 33 and 34). No Straumann implants had more than thre threads exposed. Of the Branemark/Nobel implants, 24.26% had one thread exposed (n= 49), 14.85% had two exposed threads (n= 30), 10.40% had thre exposed threads (n= 21), 4.95% four threads (n= 10) and 1.98% had five threads exposed (n= 4) (Fig 27). Straumann implants had significantly fewer exposed threads than Nobel implants (p=0.000).         71  Fig 28. Number of threads exposed over time based on surface roughnes. 56.57% of rough surface implants and 35.71% of machined surface implants had no radiographic thread exposure over time. 20.57% of rough and 22.85% of smooth surface implants had one exposed thread. Exposure of two threads was sen in 13.71% of rough and 11.43% of smooth implants. Thre threads were exposed on the radiographs in  7.43% of rough implants and 12.86% of smooth surface ones. 1.71% of rough implants and 11.43% of machined implants had four exposed threads, while 5.71% of machined implants and no rough surface implants had five exposed threads (Fig 28). As a general trend, rough surface implants had significantly les radiographic thread exposure over time than their smooth surface counterparts (p=0.000).   72 5.3 Regresion analyses  Two types of regresion analysis were completed for this report. Stepwise linear multiple regresion analysis was completed with the number of exposed threads over time as the dependent outcome variable. Logistic regresion analysis was completed with implant failure as the dependent variable. In terms of the stepwise linear multiple regresion analysis, the predictors (variables) entered included: region of the jaw of placement (posterior vs. anterior), GBR (prior or simultaneous), implant model, implant length, sinus augmentation (prior or simultaneous), implant width, jaw of placement (maxila vs. mandible) and surface type. Based on the tolerance values, the asumption for the independence of predictors was fulfiled (al tolerance values >0.750). The overal model for the thread exposure outcome was highly statisticaly significant (p=0.000) and the aforementioned predictors explained 13.3% of the variation in thread exposure. Beta values (standardized regresion coeficients) were used to compare the efect of the predictors. Such coeficients measure the change in the dependent variable that results from a one-standard-deviation change in the independent variables; zero being no efect and one being maximum efect (Schroeder 1986). The predictors showing the largest statisticaly significant efects were: implant model (β= 0.222 and p=0.001), in favor of Straumann implants, jaw in which the implant was placed (β= 0.213 and p=0.005), in favor of mandibular implants and surface type (β= 0.206 and p=0.011), rough surface being beter than machined surface. A second analysis was done with fewer predictors (only those that were significant or approached significance in the bivariate analyses were included): implant  73 model, surface type, jaw and sinus augmentation. These predictors explained 13.8% of the variance of thread exposure. The asumption for the independence of the predictors was fulfiled because al of the tolerance values exceded 0.750. The β values were 0.227 for implant model (p=0.000), 0.260 for surface type (p=0.000), 0.188 for the jaw (p=0.007), and 0.134 for sinus augmentation (p=0.037) (those without sinus augmentation had fewer exposed threads).  Logistic regresion analysis was employed with the following predictors: GBR, sinus augmentation, implant width, implant length, jaw, position (anterior vs. posterior), model type and surface type. Only sinus augmentation (p= 0.008) and implant width (p=0.018) were significant predictors of implant failure/survival. Odds ratios (OR) were used to ases the risk of implant failure if a certain predictor is present. The OR is a relative measure of risk and demonstrates how much more likely it is that that someone exposed to a risk factor under study (e.g. sinus augmentation) wil develop the outcome as compared to someone who is not exposed to it (Westergren et al 2001). The OR for implant failure was 11.00 in favor of implants placed without sinus augmentation and 0.29 in favor of increasing implant width (Table 7).  Table 7. Variables reaching or approaching statistical significance in logistic regresion analysis and the corresponding odds ratios. Predictor Odds ratio Sig. GBR (prior or simultaneous) 0.150 0.079 Sinus augmentation (prior or simultaneous 11.002 0.008 Implant width 0.288 0.018   74 When only simultaneous sinus lifts were included in the model, both sinus augmentation and implant surface were significantly asociated with implant failure (p=0.003 and p=0.023, respectively). The OR for surface was 0.30 (in favor of rough surface implants) and the OR for sinus augmentation was even higher than the previous model, 16.87.  75 6. DISCUSION  Due to incomplete pre-operative, surgical and/or radiographic records, a large portion of the available charts (42.47%) was excluded from the study. The majority of these charts were excluded due to inadequate radiographic follow up, i.e. radiographs were either not taken at follow up or the implant threads and peri-implant bone levels were not clearly visible due to poor angulation. Ensuring a diagnostic radiograph of an implant can be chalenging, particularly in situations where adjacent and/or opposing teth are not present to stabilize the film holder (e.g. completely edentulous patients). Since this is a retrospective study of implants placed over a long time period, there was no standard protocol for taking radiographs of the implants. Stents were not fabricated to ensure similar angulations at each follow-up and the radiographic technology changed from film to digital in 2006. This lack of consistency made it dificult to compare radiographs over time. For this reason, thread exposure was used as a relatively stable reference point from which to measure peri-implant bone loss over time. Implant survival was considered the first outcome variable; thread exposure was considered the second outcome measure. 6.1 Patient-level analysis 6.1.1 Distribution of implants  When implants were first introduced in the UBC grad program in the late 1990s, the majority of cases involved two implant-supported overdentures. In this study, 48.6% of patients had two implants placed, and 39% of the implants placed were restored with removable overdentures. With time, the implant clinic has evolved. By the mid-2000s,  76 residents were placing implants in al regions of both jaws, using extensive autogenous and non-autogenous bone augmentation procedures (socket preservation, guided bone regeneration and sinus augmentation), and completing full-mouth reconstruction cases. Therefore, the increasing dificulty of the cases acepted at the university may offset the expected increase in implant survival that came with advances in implant design and surface characteristics in the early 2000s. For example, if the clinic continued to acept relatively simple, two-implant overdenture cases (in which implants are likely placed in dense bone) (Misch et al., 2006; Morand and Irinakis, 2007) one would expect that the survival of implants would have improved with the introduction of rough surface implants. In reality, as the implant surface characteristics of implants improved over time, UBC residents began placing more implants in poorer quality bone (i.e. posterior maxila) (Morand and Irinakis, 2007) with more complex pre- or peri-operative bone augmentation procedures and more chalenging prosthodontic rehabilitation and maintenance. 6.1.2 Implant follow up  The mean follow up time for the implants was 4.08 + 2.95 years, which is relatively short compared to many of the large retrospective and prospective implant studies available to date (Berglundh et al., 2002; DeLuca et al., 2006a; DeLuca et al., 2006b; Eliason et al., 2006; Ferigno et al., 2002; Hardt et al., 2002; Lekholm et al., 1999; Levin et al., 2006; Romeo et al., 2004). In the present study, the shorter follow up time was acepted to increase the sample size and ensure the inclusion of newer, rough surface implants and those placed in conjunction with more complex surgical procedures  77 (autogenous grafting, sinus augmentation, etc.) that were not practiced at UBC ten years ago. That said, the maximum follow up time was 19.79 years since implant placement, indicating that we do have over 10 year follow ups for a portion of the sample. The inclusion criterion of a one-year follow up post-implant placement is comparable to many other published studies (De Boever and De Boever, 2005; Kohavi et al., 2004). The sample size does compare favorably to other publications as wel, particularly retrospective reports from university training programs (Hardt et al., 2002; Kohavi et al., 2004; Melo et al., 2006). Hardt et al.’s 2002 retrospective study included 97 patients and 346 implants and had a 5-year follow up (Hardt et al., 2002). Similarly, Kohavi et al.’s 2004 study followed 303 implants over an average of 36 months and Melo et al.’s retrospective oral surgery residency-based report followed 54 patients (175 implants) over 6 months (Kohavi et al., 2004; Melo et al., 2006). 6.1.3 Implant survival  At the patient level, 84.1% of patients experienced no implant failures. At the implant level, we found a 92.3% implant survival rate over the mean four years follow-up. These survival rates fal into the range of what is generaly found in implant literature (Brocard et al., 2000; Buser et al., 1997; DeLuca et al., 2006a; Ferigno et al., 2002; Grunder et al., 1999; Lekholm et al., 1999; Levin et al., 2006; Melo et al., 2006; Moy et al., 2005; Romeo et al., 2004; Schwartz-Arad et al., 2008).  78 6.1.4 Demographic factors  Age There were no significant diferences in implant survival based on patient age in this study. This does not concur with the findings of Moy et al. (2005) who found that advanced age doubles the risk for implant failure (Moy et al., 2005). In fact, the trend in this study was that patients in the youngest age group (>40 years) had the highest failure rate and that the oldest group (>60 years) had the highest survival rate (those betwen 40 and 59 years of age fel betwen the two other groups). Many patients in the oldest age group were two-implant overdenture cases with implants placed in the lower mandible, where reported succes rates are highest (Misch et al., 2006). It is more likely that younger patients had implants placed in areas where bone is les dense, or where the implant supported restorations were opposed by natural teth. This is similar to Dao et al.’s 1993 study, where the highest implant failure rates were found in the youngest age group. (Dao et al.,1993). As in this study, many other reports have shown that age does not have a significant impact on implant survival (DeLuca et al., 2006a; Grant et al., 2008; Lemerman and Lemerman, 2005).  Gender  In a similar way, although female patients had a higher implant survival rate than male patients in this study, the diference was not statisticaly significant. This is in agrement with a number of review papers and primary research reports in recent years. (Blanes et al., 2007; Dao et al., 1993; DeLuca et al., 2006a; Lemerman and Lemerman, 2005; Levin et al., 2007; Mombeli and Cionca., 2006; Moy et al., 2005).   79 Systemic disease  In this study, the presence of a systemic disease, such as osteoporosis or diabetes, was not significantly asociated with implant failure. This may be because so few patient charts reported systemic disease in the patient’s health history section. Of the 107 patients included, only eight had a reported history of diabetes, 24 reported hypertension, 16 arthritis and thre indicated they suffered from osteoporosis. Of these, those with the smalest sample sizes (diabetes and osteoporosis) are most likely to be asociated with implant failure – diabetes because it impacts wound healing, and osteoporosis because it afects bone mineral density and, possibly, osseointegration. Even if a diference betwen groups existed, the sample sizes were likely too smal to alow for statistical significance. Many studies and reviews, like this one, have shown that implants placed in patients with osteoporosis are similarly succesful to those placed in non-osteoporotic patients (Cranin et al., 1991; Friberg, 1994; Friberg et al., 2001; Mombeli and Cionca., 2006; Steiner and Ramp, 1990). Mombeli and Cionca’s 2006 review paper analyzed data from 17 papers and found that the evidence for an asociation betwen osteoporosis and implant failure was low (Mombeli and Cionca, 2006). Moreover, bone-to-implant contact and bone maturity around implants is also comparable (de Melo et al., 2008; Shibli et al., 2008a; Shibli et al., 2008b). In this study, diabetic patients were no more susceptible to experiencing implant failure than non-diabetics. This is unlike Moy et al.’s 2005 retrospective study (largely machined surfaced implants), which stated a relative risk of 2.75 for implant failure in diabetics (even if they are wel controlled) (Moy et al., 2005). Others have agred with Moy’s conclusions (Fiorelini et al., 2000; Nevins et al., 1998).  80 Conversely, there is compeling evidence that implants are as succesful in controlled diabetics as they are in non-diabetic patients (Mombeli and Cionca, 2006; Olson et al., 2000b; Peleg et al., 2003; Shernof et al., 1994). As discussed above, if there was a true diference in implant survival betwen diabetics and non-diabetics in this study, the sample size was likely too smal to show a statisticaly significant diference. In addition, the level of diabetic control at the time of placement or throughout the follow up period could not be determined, since there is limited data of this kind in the patient chart. If this study was to be done prospectively and we had a large sample of diabetic patients, control could be monitored with periodic asesment of glycosylated hemoglobin (HbA1c) levels throughout the study. 6.1.5 Smoking status  Smoking has been linked to increased implant failures in numerous reports (Aykent et al., 2007; Baelum and Elegard, 2004; Bain and Moy, 1993; De Bruyn, 1994; DeLuca et al., 2006a; Hinode et al., 2006; Karoussis et al., 2003; Mombeli and Cionca, 2006; Moy et al., 2005; Olson et al., 2000a; Walace, 2000; Widmark et al., 2001). Some, particularly those published in the 1990s, demonstrated a large (over 2x) diference in survival rates betwen smokers and non-smokers (Baelum and Elegard, 2004; Bain and Moy, 1993; De Bruyn et al., 1994). However, more recent studies have did not find a significant diference in implant survival betwen smokers and non-smokers (Bain, 2002; Blanes et al., 2007; Brocard et al., 2000; Kumar et al., 2002; Levin et al., 2007; Peleg et al., 2006a; Schwartz-Arad et al., 2002; Schwartz-Arad et al., 2008). Advances in surface topography of the implant appear to have increase survival rates to the point where the efect of smoking is negligible (Kumar et al., 2002). In this study, there was a trend for  81 current smokers to have more implant failures than never or former smokers, but this was not significant. This relationship may not be statisticaly significant due to the smal sample size, or because a majority of the implants placed (68.55%) were modern, rough surface implants which are usualy asociated with higher survival rates (Morand and Irinakis, 2007). 6.2 Implant level analysis 6.2.1 Implant design  Implant brand  There was a diference in survival rates betwen the implant systems used at UBC, in favour of the Straumann ITI system, but this diference was not statisticaly significant. Similar findings were reported in Meijer et al.’s 2009 overdenture study, which stated that ITI implants had a higher, but not significantly so, survival rate compared to Nobel Biocare implants (100% vs. 98%) (Meijer et al., 2009). At UBC, many factors may have impacted the high implant survival in ITI cases. Firstly, al of the Straumann implants placed were rough surface implants, whereas 33.06% of Nobel implants had a machined surface. That said, there was no significant diference in implant survival betwen rough and smooth Nobel implants. Secondly, Straumann implants were introduced into the grad perio program in 2002, therefore we have shorter follow up times and les opportunity for long term failures to be recorded in the study. Thirdly and perhaps most significantly, Straumann implants have traditionaly been placed only with visiting instructors and these cases tended to be les complex since the instructor wasn’t available for extensive treatment planning prior to the surgical date. In this way, those ITI implants that have been placed may be biased for succes since  82 they were rough surface implants with relatively short follow ups and they were likely placed in relatively simple clinical cases. That said, a large systematic review of the survival rates of implant supported fixed partial dentures published in 2004 found that Branemark Nobel Biocare implants were the only type to have below average survival rates, while al other brands (including ITI) had survival rates above the study average (Pjeturson et al., 2004). In the available implant literature, both systems show high implant survival rates. For the Straumann/ITI system, Buser et al.’s multicentre study of 2359 implants found that 96.7% of implants survived at 8 years (Buser et al., 1997). Romeo et al.’s 2002 paper followed 187 implants restored with single crowns over 7 years and reported a 96.77% survival rate (Romeo et al., 2002). He then published a 7-year study of 759 implants restored with various removable and fixed appliances and found that survival rates ranged from 94.4-100% for prostheses supported only by implants (Romeo et al., 2004). Similar high survival rates have been reported in many other studies, including this one (100% survived) (Ferigno et al., 2001 – 95.9%, Brocard et al., 2000 – 92.2%, Blanes et al., 2007 – 97.9%) (Blanes et al., 2007; Brocard et al., 2000; Ferigno et al., 2002). In terms of the Branemark/Nobel implant system, high survival rates have also been reported. Eliason’s 2006 study on 2- and 3-implant supported prosthesis followed over 9 years, reported survival rates from 96.8-98.4% (Eliason et al., 2006). In Friberg and Jemt’s 2009 report, implant failure rates varied from 0.9-2.9% (Friberg and Jemt, 2009). Ekelund et al. reported a 98.9% 20-year survival rate for Branemark implants in 2003 (Ekelund et al., 2003). In another multicentre study, 96.6% of implants placed in the maxila and 100% of those placed in the mandible survived 5 years (Henry et al.,  83 1996). High implant survival rates with this brand of implant have been demonstrated in many other published reports (DeLuca et al., 2006a; Lekholm et al., 2006; Roos-Jansaker et al., 2006; Turkyilmaz et al., 2007). The mean implant survival rate of 92.3% over a mean of 4 years in the present study is comparable to the rates reported in the above publications.  Implant surface  When machined and rough surface implants were considered separately, the survival rates were 90.9% and 92.8%, respectively. These rates were not significantly diferent in the bivariate analysis. The survival rates for machined surface implants in this study were higher than many of the clasic studies, but our follow up period was much shorter and our criteria for succes was les stringent (Atard and Zarb, 2004). Many studies have come to similar conclusions – survival rates are not significantly diferent betwen smooth and rough surface implants. Friberg and Jemt had two groups: a mixed group with 110 machined and 68 rough implants, and a rough only group with 212 TiUnite implants (Friberg and Jemt, 2009). Implants were followed for 5 years. One machined (0.9%) and two rough (2.9%) implants failed in the mixed group, and thre rough (1.6%) implants failed in the rough-only group (Friberg and Jemt, 2009). They concluded that the survival rates for both implant types were favorable and not diferent from each other, as did Halman et al. (2005) (Friberg and Jemt, 2009; Halman et al., 2005). Similarly, in Al-Nawas et al. (2007)’s study, they also found no significant diferences in survival betwen rough and machined implants, although those with rough surfaces had an advantage in poorer quality bone (Al-Nawas et al., 2007).  84 In our multivariate analysis, when a number of variables were controlled for (GBR, implant length and width, location in the jaw, implant model and simultaneous sinus augmentation), machined surface implants were significantly asociated with implant failure, with an efect size of 0.30. Much of the available research agres that rough implants do sem to have the most favorable survival rates. Khang et al. (2001) found cumulative succes rates of 95.0% for acid-etched implants and 86.7% for machined implants (Khang et al., 2001). As in Al-Nawas study, the performance diference was greatest in poor quality bone like the posterior maxila (96.8% for acid etched and 84.8% for machined) (Al-Nawas et al., 2007; Khang et al., 2001). Machined implants were not as succesful as rough implants in soft bone in Stach and Kohles’ 2003 report as wel (Stach and Kohles 2003). In Del Fabbro et al.’s systematic review of imediately loaded implants, rough surfaces had higher survival rates than machined in al types of reconstructions (Del Fabbro et al., 2008b). Similarly, machined implants were found to fail twice as often as rough implants (4.6% versus 2.3%) in a retrospective study of 1925 implants placed over 22 years (Wagenberg and Froum, 2006). The smal sample size in this study may prevent a true diference (2%) to be sen as statisticaly significant in the bivariate analysis, but this diference became apparent when other variables were controlled in the regresion analysis.  Implant dimensions  In the present study, there was also a trend towards increasing implant failure rates with decreasing implant width (4.0% wide; n=1 failed implant, 5.1% regular; n= 8 failed implants, 11.8% narow; n= 13 failed implants), but these diferences were not statisticaly significant. The efect of implant length was also studied and short implants  85 were not statisticaly more likely to fail (7.1%) than long implants (8.0%). The surface area is so extensive on rough implant surfaces compared to machined surface implants, the length and width may be les critical to improve surface area for osseointegration, provided primary stability is possible (Morand and Irinakis, 2007). Many papers conclude that short implants are just as succesful as long ones (Blanes et al., 2007; Brocard et al., 2000; Grant et al., 2009; Levin et al., 2006; Misch et al., 2006; Morand and Irinakis, 2007; Romeo et al., 2004). This is in contrast to other studies evaluating machined implants, which found that longer implants were superior to shorter ones (DeLuca et al., 2006a; Grant et al., 2009; Grunder et al., 1999; Lekholm et al., 1999; Renouard and Nisand, 2006). Width does not appear to significantly impact implant survival either (Levin et al., 2006; Morand and Irinakis, 2007; Renouard and Nisand, 2006; Romeo et al., 2004). Where a longer implant is not possible it sems prudent to atempt to place a wider one, to maintain as much surface area for osseointegration and primary stability as possible. Increasing the diameter of the implant improves surface areas more than twice as much as increasing the length (Petrie and Wiliams, 2005). Since it appears as though implant length and width are not major determinants of survival, the implant dimensions should be dictated primarily by the surrounding anatomic structures, the available bone, the type of bone and the prosthetic space. As a general rule, the longest and widest implant that can be properly and estheticaly restored should be considered (Morand and Irinakis, 2007).   86 6.2.2 Previous periodontal disease  The efect of a history of periodontal disease on implant survival was also studied. The only available indicator of disease (a rather crude measure) was the reason for tooth loss prior to implant placement. The sample was divided into groups: teth lost due to periodontal disease, teth lost for non-periodontal reasons, and teth lost for unknown or uncharted reasons. A smal portion of the sample (17.0%) had lost teth due to periodontitis, but a much larger portion (47.0%) did not have the reasons for loss acurately reported in the chart. Although there was a trend for those with teth lost due to periodontitis to also have implants fail (23.53% versus 5.56%), this relationship was not statisticaly significant. If a true efect exists, one needs to have a more acurate measure of disease history and a larger sample size for it to be elucidated. In addition, the efect of a periodontal pocket or furcation involvement on a tooth adjacent to the implant site was investigated. Implants adjacent to such teth did not suffer significantly more failures. Again, if an efect exists, the smal sample size may not alow the trend to reach statistical significance. In this study only 29 implants were asociated with adjacent pocket depths of greater than 3 m and 24 were placed adjacent to furcation involvements. Furthermore, if only deep pockets (n= 8 for PD > 5 m) or severe furcation involvements (n= 9 for Clas I involvements) (which could theoreticaly pose the greatest risk) are considered, the sample size would be further compromised. In Karoussis et al.’s 2003 clinical study, despite regular supportive therapy, patients who lost teth due to periodontitis had higher long-term failure rates than those who lost teth for other reasons (9.5% versus 3.5%). Those with a history of the disease also had a much higher incidence of peri-implantitis. Similarly, Hardt et al. (2002)  87 published a study where patients were grouped based on age-related bone loss score. Again, the implant failure rate was higher in the periodontitis group (8.0% versus 3.3%) (Hardt et al., 2002). Similar findings were reported in many other papers, including a recent systematic review (Brocard et al., 2000; Grunder et al., 1999; Safi et al., 2009; Schou et al., 2004). 6.2.3 Pre- or peri-operative bone augmentation  A large part of implant dentistry today involves creating bone where it has been resorbed in order to place an implant of ideal dimensions in the best possible position for prosthodontic rehabilitation. The techniques used to achieve this bone augmentation include socket preservation, guided bone regeneration with particulate or block bone grafts, and sinus augmentation with osteotomes (at the time of implant placement) or with the lateral window technique (several months prior to implant placement). Al of these techniques are commonly used in the graduate periodontics program at UBC, but many recent cases have not been included because they did not met the cut-off of 1-year post-placement follow up time at the data collection phase of this study.  Socket preservation  Socket preservation did not have a significant efect on implant survival. Although the utility of socket preservation has been questioned (Fickl et al., 2008), most researchers agre that placing implants in grafted bone does not impact their survivability (Fugazotto, 2005; Kohal et al., 1998). Many studies, including those done on animals, have found that socket preservation can beter preserve the dimensions of the alveolar ridge post-extraction (Araujo and Lindhe, 2009; Cardaropoli and Cardaropoli, 2008;  88 Irinakis, 2006; Lekovic et al., 1998). Resorption of the alveolar crest without socket preservation can make implant placement more chalenging, since the width of the ridge can decrease by 50%, with 2/3 of this loss occurring in the first thre months (Schropp et al., 2003). However, the most critical factor for preservation of ridge dimensions appears to be atraumatic extraction of the tooth (Fickl et al., 2008; Irinakis, 2006).  Guided bone regeneration  Guided bone regeneration prior to implant placement had a nearly significant efect on implant survival (98.1%, p=0.091, n=58). When the bone graft was done at the time of implant placement, the efect on survival was not significant (p=0.377, n= 18). 40.39% of the guided bone regeneration that was completed prior to implant placement was done with a xenograft material (Bio-Os®) and a resorbable membrane (Bio-Guide or NeomemTM). 51.92% of cases were grafted with autogenous bone, either from the iliac crest by referal to an oral surgeon, or via intraoral graft done in the graduate clinic at UBC. A smal percentage, 7.69% of cases used another source of grafting material – either an alograft (DynagraftTM) or hydroxyapatite with a resorbable membrane. 5.77% of al cases used a non-resorbable membrane (GORE-TEX®) in conjunction with the bone grafting material. As discussed in the introduction section of this paper, many studies support that implants placed into grafted bone have comparable survival and succes rates to implants placed in native bone (Aghaloo and Moy, 2007; Blanco et al., 2005; Brocard et al., 2000; Christensen et al., 2003; De Boever and De Boever, 2005; Esposito et al., 2006; Fiorelini et al., 2003; Fugazotto, 2005; Halman et al., 2002; Juodzbalys et al., 2007; Simion et al., 2001). When both GBR procedures were considered together, there was a  89 significantly positive efect of bone augmentation on implant survival. The reason for this is unknown and dificult to explain. This trend may be due to the fact that GBR was adopted into the program in the mid-2000s, at the same time as advances in implant surface topography were also taking place. A large proportion of implants placed with GBR were likely rough surface implants. GBR may also indicate that the case was wel planned and that fixtures were not placed into bone whose dimensions were not ideal for implant placement or at angulations that were les than ideal for the future restorations.  Sinus augmentation   In terms of sinus augmentation, al of the included cases that had a lateral window sinus lift prior to implant placement were completed with Bio-Os®, a xenograft material and Bio-Guide, a resorbable membrane over the window. None of the implants placed after these sinus lifts failed, i.e. the augmentation did not significantly impact implant survival. This is in agrement with many studies, which indicate that implants placed in augmented sinuses have survival and succes rates similar to implants placed in the posterior maxila without sinus augmentation (Aghaloo and Moy, 2007; Esposito et al., 2006; Sorní et al., 2005; Walace and Froum, 2003). These findings also paralel what we discussed about GBR; augmented bone appears to cary comparable succes rates to native bone.  On the other hand, osteotome sinus lifts were significantly asociated with more implant failures (5 out of 14 implants placed with this technique failed). In fact, the odds ratio for osteotome lifts and implant failure was 16.87. This finding is in contrast to the high succes rates for this technique in the available dental literature (Fermergard and Astrand, 2008; Ferigno et al., 2006; Pjeturson et al., 2009; Tan et al., 2008). Pjeturson  90 et al. (2009) looked at 252 Straumann implants placed over 5 years. The cumulative survival rate for the osteotome-instaled implants was 97.4% over an average of 3.2 years (Pjeturson et al., 2009). A recent meta-analysis found an estimated annual failure rate of 2.48% and an estimated overal survival rate of 92.8% for implants placed with this method (Tan et al., 2008). These results are quite diferent from the 26.34% failure rate in the present study; it is dificult to explain why cases in this study included more failures. This may be related to practitioner inexperience or that it is a technique not often practiced in the clinic. One can argue that it is a technique sensitive surgery that requires skil and experience, but the same can be said for the lateral window sinus augmentation technique, for which UBC has no failures in this report. Al of the failures occurred betwen 2005 and 2006, were grafted with BioOs® and were completed by thre diferent surgeons at diferent levels of training. With the exception of one case with 4m of residual bone, al had more than the recommended 6mm of bone for primary implant stability (Walace and Froum, 2003). Four of the five failures were early while one occurred after restoration of the implant. In searching for reasons behind these failures, it became evident (personal information provided by the supervising surgeon) that a cluster of cases was completed with a more conservative surgical protocol. After the primary osteotomy site was prepared, osteotomes were used with 2 m (instead of 0.5-1 m) of residual bone height at the sinus floor. This was done to reduce the likelihood of sinus perforations by inexperienced surgeons. The result may have been excesive trauma to the surrounding bone from extreme force used while atempting to fracture the sinus floor for an extended duration of time, which ultimately lead to an increased failure rate. Clinic protocol as since been modified.  91 When both techniques were combined, sinus lifts in general were significantly asociated with implant failure. This is likely because there were more osteotome lifts in the sample, which had a large impact on survival and skewed the results towards failure. 6.2.4 Asesment of the implant site at the time of fixture placement  Primary stability  The relationship betwen implant torque at the time of placement and implants survival was evaluated. Lower torque was significantly asociated with implant survival. One cannot generalize from this finding, since a large majority of the included cases did not have a torque recording in the chart. Only 80 out of the 300 implants (26.67%) had a torque measurement recorded. In some studies, higher torque has been thought to be asociated with beter implant survival and beter bone density, provided it is within a range that is biologicaly compatible with maintenance of crestal bone vitality (Otoni et et al., 2005; Turkyilmaz and McGlumphy, 2008). One study found that, after 3 years, 280 succesful implants had a mean bone density of 645 + 240 HU and mean insertion torque of 37.2 + 7 Ncm while 20 failed implants had lower bone density (267 + 47 HU) and lower primary stability (21.8 + 4 Ncm) (Turkyilmaz and McGlumphy, 2008). Another study found that the risk of implant failure decreased by 20% for every 9.8 Ncm added to the insertion torque (Otoni et al., 2005). In other reports, insertion torque did not impact on long-term implant survivability (Al-Nawas et al., 2006; Degidi et al., 2006). The diference in mean torque betwen failing and surviving implants was only 4.5 Ncm. Given that the torque wrench used at UBC (Nobel BioCare) is labeled with a scale in 10 - 15 Ncm increments, a reading is likely an estimated value betwen two lines on the scale. The mean diference betwen groups is smaler than one increment on the  92 scale and may reflect our inability to measure the torque precisely. There is also a large amount of variability in torque values for implants in both groups. It would be unfair to draw any conclusions from such a smal diference in mean torque given the smal number of cases with charted torque values and the high degre of variability.  Subjective assesment of the implant site  Higher failure rates have been asociated with implants placed in bone that the clinician observes to have poor mineralization or limited resistance to driling (Turkyilmaz and McGlumphy, 2008). Acording to the results of this study, the clinician’s asesment of bone quality, degre of resorption and vascularity at the time of surgery was not significantly asociated with implant survival. An equal number of failed and survived implants were also deemed to have “excelent” primary stability by the surgeon. In a similar study, a surgeon’s asesment of bone quality at the site of implant placement was recorded for 2,867 fixtures and retrospectively analyzed 3 years later. Implants placed in “good-quality” bone (as asesed subjectively at the time of placement) had significantly beter survival than those placed in “moderate-quality” or “poor quality” bone (Holahan et al., 2009). Since this is a completely subjective measure, it is presumed that the acuracy of the asesment may depend on the clinical experience of the surgeon. The clinical experience of the periodontology residents is likely far les than that of the surgeon in this study. This was the only other study found to ases the acuracy of the surgeon’s surgical asesment on long-term survivability of fixtures.  93 6.2.5 Implant site  Jaw and region of placement   The diference in succes rates as it relates to jaw and implant position is often atributed to bone quality (Turkyilmaz and McGlumphy, 2008). Generaly anterior sites have beter bone density than posterior sites, and the mandible is more dense than the maxila (Misch et al., 2006; Morand and Irinakis, 2007; Turkyilmaz and McGlumphy, 2008). Poor bone quality has been strongly linked to higher failure rates in implants, particularly for those with smooth surfaces (Morand and Irinakis, 2007). The present study did not show a significant diference in survival rates for implants placed in the maxila or mandible, although there was a trend for those in the mandible to fail more often. There was also no significant diference betwen implant survival rates in anterior versus posterior sites, but there was a trend that favoured posterior implants. Both of these trends oppose what is commonly found in the implant literature (mandibular and anterior implants are generaly considered most succesful) (DeLuca et al., 2006a; Grunder et al., 1999; Hinode et al., 2006; Lekholm et al., 1999; Moy et al., 2005; Romeo et al., 2002), but it is important to remember that there was no significant diference in either case. Many studies do agre that, since the introduction of rough-surface implants, diferences in succes rates betwen jaws or bone types are smal and often not statisticaly significant or clinicaly relevant. (Aykent et al., 2007; Brocard et al., 2000; Kumar et al., 2002; Polizi et al., 2000; Romeo et al., 2004)  When jaws were considered separately, implants in the posterior maxila tended to fail more often than implants placed in the anterior maxila, but the diference was not significantly diferent. There was also no significant diference in survival rates for  94 mandibular implants, but anterior implants tended to have higher failure rates. This finding may be because the sample is largely skewed for mandibular overdenture cases, many of which were placed in the early stages of the implant program when implants had machined surfaces. Many publications report beter survival in the anterior regions of both jaws, (Ferigno et al., 2002; Moy et al., 2005) while others, like ours, found no significant diferences (Brocard et al., 2000; Polizi et al., 2000). 6.2.6 Post-operative chemotherapy  With very few exceptions, antibiotics were given to patients at UBC after implant placement. In almost thre-quarters of the cases amoxicilin, a moderate-spectrum, bacteriolytic β-lactam antibiotic, was prescribed. Chlorhexidine, a chemical antiseptic rinse, was also prescribed in thre-quarters of cases. Despite the prescription of post-operative antibiotics and oral rinses, infections were asociated with 5.7% of implants placed in the grad program.  A Cochrane review as completed to determine if antibiotics at the time of implant placement prevent complications post-surgery (Balevi, 2008). Two randomized control trials with folow-ups of at least 3 months were included (Balevi, 2008). A meta-analysis showed that there was a significantly higher number of patients experiencing implant failures in the group not receiving antibiotics (Balevi, 2008). The number needed to treat to avoid one implant failure due to infection was 25, based on an implant failure rate of 6% for those not taking antibiotics (Balevi, 2008). This study recommends a loading does of antibiotic at the time of implant surgery but makes no conclusions about the benefit of post-operative antibiotics (Balevi, 2008).  95 6.2.7 Post operative complications  In general, most dental surgery procedures are considered Clas 2 by the American College of Surgeons Commite on Control of Surgical infections (Clas 1 being the cleanest and least likely to become infected and Clas 4 being “dirty” or infected surgery sites). Theses are known to cary a post-operative infection rate of 10% to 15%, but with proper surgical technique and prophylactic antibiotics, the incidence of infection may be reduced to 1% (Resnik and Misch, 2008). Obviously, the infection rate in this study is higher than 1%. We have to keep in mind that this rate was considered on an implant basis and not a patient or case basis – if two implants placed in the same surgery site became infected it was viewed as two separate events, and not one case of infection. The protocol at the university requires that extensive patient draping, instrument sterilization, hand scrubbing, sterile gowns and gloves for students and staf as wel as proper disinfection procedures for the equipment are completed for each surgery. Residents in training completed the majority of surgeries included in this report and the duration of the surgery (the time the flap is open) is likely much longer than it would be with a more experienced clinician. The duration of surgery is considered the second most critical factor (after wound contamination) for causing post-operative infections (Resnik and Misch, 2008). Operations that last les than one hour have an infection rate of 1.3% compared to 3-hour long surgeries that cary a risk of 4.0% (Resnik and Misch, 2008). It has been reported that the rate of infection doubles with each additional hour (Resnik and Misch, 2008).  96 The incidence of bleding problems in this study was 1.9%. This is based on information in the daily record that the patient complained of bleding problems during the healing phase, or that the patient presented with an uncontrolled bled to the clinic. The findings may not be acurate because they depend solely on acuracy in charting, there is no way to appreciate how significant the bleding problems were and patients may have sought treatment elsewhere (another dentist, hospital emergency room, etc). We also have only superficial information about any bleding disorders the patients may have, and therefore we cannot draw any conclusions about why certain cases had bleding isues while most others did not. The incidence of both temporary and permanent paresthesia was 0.67%. This translates into one patient who experienced temporary paresthesia after implant placement in 1998 and one patient who experienced permanent paresthesia after implants were placed in 2000. Both patients had implants placed in the anterior mandible. Due to the timing of placement, neither of these cases had any 3-dimensional imaging prior to implant placement, which is now routine at UBC. Of the implants included in this study since the introduction of 3-D imaging in this clinic, no paresthesia has been reported. Computerized tomography (CT) scans are more acurate for detecting anatomic structures in the region of implant placement and should be used when traditional films do not provide clarity of nerve position (Grenstein and Tarnow, 2006). Our rate of temporary paresthesia is similar to that reported by Vazquez et al. (2008) who found that 0.8% of patients with implants placed in the mandible had temporary sensory disturbances that resolved spontaneously (Vazquez et al., 2008). Of the 2584 implants placed, they had no reported cases of permanent paresthesia despite the  97 fact that al cases were planned with panoramic radiographs (Vazquez et al., 2008). In a much earlier study, 266 patients with implants placed in the mandible were given a questionnaire (Elies, 1992). 80% responded and 37% reported altered sensation after implant surgery with long term changes in 13% of patients (Elies, 1992). In Bartling et al.’s (1999) study, 8.5% of patients with mandibular implants experienced altered sensation post-operatively but none had permanent nerve damage (CT scans were only used when the mandibular nerve wasn’t clear on the panoramic radiograph) (Bartling et al., 1999). In another study, 24% of patients had neurosensory disturbances after implant placement in the anterior mandible, but les than 1% had any paresthesia 1 year after surgery (Walton, 2000). From these reports, it appears that temporary sensory disturbances are quite common after mandibular implant placement but permanent damage is rare. 6.2.8 Implant restoration  Distribution of implant-supported restorations  A large portion of implants in this study was restored with removable overdentures (39.0%), while 29.0% of the implants were restored with splinted crowns, 15.0% with single crowns, 10.0% with fixed partial dentures and 7.0% with fixed full-arch hybrid dentures. The sample is skewed for removable denture cases because when implants were first introduced at UBC, the vast majority of acepted cases were two-implant mandibular overdentures. There was a close to 10% diference in survival rates betwen implants restored with removable prostheses (89.9% survival) and those restored with fixed prostheses (98.8%). Aykent et al. (2007) also found that implants restored with  98 removable prostheses fared worse than those with fixed restorations (90.2% vs. 95.2% over 1-12 years) (Aykent et al., 2007).   Prosthodontic complications  Over two-thirds of patients experienced at least one prosthodontic complication during the follow up time. Almost thre-quarters of the reported complications were asociated with removable prostheses. Not only were implants more likely to fail in overdenture cases, but the patients were also more likely to experience prosthodontic isues during follow up. Kaufmann et al. reported frequent technical complications with dentures, mostly related to the anchorage systems to the implants (Kaufmann et al., 2009). These complications were more frequently observed in the first year after delivery of the prosthesis (Kaufmann et al., 2009; Kiener et al., 2001). In 2002, a study by Chafe et al. followed 58 patients with implant supported removable overdentures over 36 months (Chafe et al., 2002). Of the 58 patients, 6 required no adjustments, while the remaining 52 patients required 327 return visits (194 of these were unscheduled) for prosthesis or abutment adjustments (Chafe et al., 2002). Undergraduate students have restored many of the overdenture cases at UBC, whereas the fixed implant-supported restorations were completed exclusively by prosthodontists. This may acount, in part, for the higher number of post-placement prosthodontic complications for removable dentures who were often restored by relatively inexperienced students. Also, Walton et al. (2001) described that inexperienced surgeons (much like the periodontology residents at UBC) had a greater tendency to place implants at les-than-ideal angulations (Walton et al., 2001). This study showed a  99 significantly greater number of denture repairs were required when the lingual inclination of implants was greater than or equal to 6mm (Walton et al., 2001). 6.2.9 Level of training of the clinician   Although not significant, there was a trend for implants placed by residents in their second year of training to have lower survival rates than those placed by first or third year residents, or staf members. In fact, almost half of al failed implants (46.67%) were placed by students in their second year of the program. The high implant survival rate found with those in their first year of training (94.12%) may be because these residents were likely asigned the most simple implant cases (adequate dimensions of existing bone, generous distance betwen implant position and any anatomic structures, implants placed in highly dense bone, etc.). Second year students were likely asigned more chalenging cases while they continued to develop their surgical skils, which may explain the relatively low implant survival rate (88.54%). Third year residents and staf have already undergone extensive clinical and didactic training in implant dentistry, and thus the implants they placed demonstrated relatively high survival rates (97.62% and 93.18%). Staf may have lower succes rates than the third year residents because they likely took on the most dificult cases. Some studies have found that clinician experience and/or training does impact implant survival (DeLuca et al., 2006a; Lambert et al., 1997). One study found that implants placed by inexperienced surgeons were twice as likely to fail, especialy if the case was one of their first nine cases (Lambert et al., 1997). In a recent publication by Eliason et al. (2009), 109 patients had implants placed and 13 patients had fixtures placed by inexperienced surgeons (Eliason et al., 2009). Al thre patients who  100 experienced failures were treated by the smal group of inexperienced surgeons (Eliason et al., 2009). The lack of a statisticaly significant diference betwen implants placed by students at various levels in their training in this study may be related to the close supervision of al residents by an experienced clinician, which may help to lesen the learning curve. Like this investigation, Kohavi et al. (2004) and Melo et al. (2006) also studied university training programs and found that the level of experience did not significantly efect implant survival (Kohavi et al., 2004; Melo et al., 2006). Melo et al. explained the trends in their study based on the level of complexity of the cases given the residents in that program (Melo et al., 2006). 6.2.10 Replacement implants  Should an implant fail, it is important to know if the survival of a replacement implant is comparable to the published survival rates for implants in general. Mardinger et al. (2008) studied 120 patients with implant failures who chose to have replacement implants and 74 patients with implant failures who chose not to have new implants (Mardinger et al., 2008). They found that the major factor that impacted the patient’s decision to replace the implant was the amount of bone loss at the implant site (Mardinger et al., 2008). The tendency to choose reimplantation correlated with the amount of bone loss and the need for augmentation (Mardinger et al., 2008). Reasons patients gave for avoiding reimplantation included: the additional cost (27% of patients), fear of pain (17.7%), fear of second failure (16.2%), proximity to anatomic structures (16.2%), no prosthetic needs for a new implant (12.1%) and medical status (10.8%) (Mardinger et al., 2008).  101 Currently, very few reports mention the survival rates of replacement implants (Mardinger et al., 2008). One study examined 79 replacement implants and followed them for 7 to 78 months (Machtei et al., 2008). The overal survival rate for was 83.5%, which is lower than reported by most studies for implants placed in pristine sites (Machtei et al., 2008). Grossmann and Levin (2009) also reported low survival rates for replacement implants (71% over 6 to 46 months) (Grossmann and Levin, 2007). In Alsadi’s (2006) report, 29 machined surface implants were replaced by other machined surface implants and six of these failed (79.4% survival rate) (Alsadi et al., 2006). On the other hand, when 19 failed smooth-surface implants were replaced with rough implants only one implant failed and when 10 rough implants were replaced with the same surface, none failed (Alsadi et al., 2006).  The replacement implant survival rate of 85.71% compares favorably to the above-mentioned reports. This relatively high survival rate may be asociated with the very smal sample size (n=14). There is stil a lack of substantial evidence regarding failed implant replacement. Many studies advocate meticulous removal of al granulation tisue around the implant site and the use of wider implants with improved surface texture to ensure the best long-term treatment outcome (Mardinger et al., 2008). 6.2.11 Peri-implant bone loss  Almost twice as many Branemark/Nobel BioCare implants had thread exposure over time compared to Straumann implants. Of al of the predictors in the multivariate analysis, implant model had the largest significant efect on thread exposure (β=0.22). A recent meta-analysis did find that Straumann implants had significantly les marginal bone loss than Branemark/Nobel implants; the pooled mean marginal loss was 0.48 m  102 and 0.75 m respectively, over five years (Laurel and Lundgren, 2009). It is dificult to use thread exposure as a comparison for horizontal bone loss with these two systems since the implant designs are very diferent (appendix H, fig 33). For Straumann implants, the distance from the lower edge of the smooth neck (the point at which most soft tisue level implants are submerged) to the first thread is 1.25-2.25 m. In the Branemark/Nobel system, the distance from the point of usual submersion (the edge of the smooth collar in Select implants, the top of the fixture in Groovy and Mk implants) to the first thread is betwen 0.3 and 1.5 m (depending on the design). It is important to emphasize that, due to the diference in design, more marginal bone loss has to occur around a Straumann implant to expose the first thread. Another reason this comparison may be unfair is because so few Straumann implants were placed relative to the number of Branemark/Nobel implants. Until recently, Straumann implants were placed only under the supervision of a visiting instructor, who was not generaly available for treatment planning prior to surgery. For this reason, the sample is likely skewed towards more simple cases, as residents tend to reserve the most dificult cases to be done with the instructor with whom they planned it. The level of thread exposure for Branemark/Nobel implants was high when compared to other published reports. In a 2000 investigation of 4971 implants, marginal bone loss exceding the first thre threads occurred in 1.8% of implants (mean follow up time, 5.1 years) (Snauwaert et al., 2000). In this study, 5.0% of Branemark/Nobel had four threads exposed and 2.0% had five exposed. In another publication limited to machined surface Branemark implants, only 183 out of 3,462 implants had marginal loss of >3 m from the fixture/abutment interface with most loss occurring in the first year  103 after placement (Pikner et al., 2009). It is dificult to explain why the Branemark implants were asociated with more peri-implant bone loss than what is generaly found in the literature. The lack of any standardization of radiographic measures in this study makes the value of our marginal bone loss measures questionable. If marginal bone stability is related to the preparation of the bone at the time of surgery, it is plausible that surgical factors may be implicated in this increased loss (residents likely have the flap open longer, may be more liable to overheat the bone than more experienced clinicians). 6.3 Regresion analyses  Regresion analysis is a technique for modeling the relationship betwen two or more variables (Miles, 2001). Stepwise linear multiple regresion analysis was completed for thread exposure, while logistic regresion analysis was completed for the dichotomous primary outcome variable – implant failure. Implant model had a statisticaly significant efect on tread exposure, in that Straumann implants were les susceptible to having threads exposed over time. As previously discussed, this maybe largely due to the diference in implant design and case selection betwen Nobel and Straumann (appendix H, fig. 33). Mandibular implants were found to have les thread exposure than maxilary implants and rough surface implants had les marginal bone loss than their smooth counterparts. These findings are consistent with the low failure rates of mandibular and rough surface implants commonly published (Del Fabbro et al., 2008b; DeLuca et al., 2006a; Grunder et al., 1999; Hinode et al., 2006; Khang and Flier, 2001; Lekholm et al., 1999; Moy et al., 2005; Romeo et al., 2002; Stach and Kohles, 2003). Significant diferences were not found when examining surface texture and jaw bone in the bivariate analyses but a clear efect on thread  104 exposure could be sen after controlling for confounding variables. When fewer predictors were considered in the regresion analysis, sinus augmentation was also asociated with increased thread exposure. In terms of implant failure, only sinus augmentation and implant width were found to have significant efects after logistic regresion analysis. The odds ratio for implant failure was 11.00 for those with sinus augmentation (16.87 if only simultaneous lifts were considered) and 0.288 for those with narower implants. This clearly indicates that sinus augmentation was the most significant predictor of implant failure in the present study. As discussed previously, this finding is likely skewed by the relatively high implant failure rate for implants placed with simultaneous osteotome lifts. This is contradictory to the high succes rates for this technique in the curent literature (Fermergard and Astrand, 2008; Ferigno et al., 2006; Pjeturson et al., 2009; Tan et al., 2008). 6.4 Study limitations  Many of the drawbacks of this type of retrospective chart review have been discussed in previous sections of this paper. A summary is presented below: a) Smal sample size b) Large number of excluded cases  c) Retrospective design   d) Important data not always available  e) Relies on acuracy of chart records  f) Unable to prove cause and efect g) Diferent types and designs of implants placed  105  h) Lack of randomization and blinding Given the high survival rates of implants (including those placed in this program), a smal sample size does not alow for trends in the data to reach statistical significance, even if a true diference exists. An analysis of the baseline characteristics of the excluded cases (age and gender) demonstrated that there were no significant diferences in these characteristics betwen the study patients and the excluded patients (p=0.152 and p=0.224). 6.5 Conclusions The following conclusions can be made in the context of this investigation: • Implants placed at the UBC graduate periodontics clinic betwen 1989 and 2006 had a survival rate of 92.3%, which compares favorably to rates reported in the literature. • 84.1% of patients treated in this clinic had no implant failures. • 13.1% of patients had one failed implant, 2.8% of patients had two failed implants, and no patients had more than two implant failures. • The survival rate for replacement implants was 85.71%. • Most variables considered risk factors did not have a statisticaly significant impact on implant survival. • In the bivariate analysis, only sinus augmentation (particularly indirect, simultaneous elevations) was significantly asociated with implant failure and guided bone regeneration was significantly asociated with implant survival.  106 • In the regresion analyses, the predictors showing the largest efect on thread exposure were: implant model, jaw (in favor of mandibular implants) and surface (in favor of rough surface implants). • The odds ratio for implant failure was 0.30 for machined surface implants and 0.29 for decreasing implant width. • The odds ratio for implant failure was 16.87 when an indirect osteotome lift was employed. Overly conservative approaches to osteotome sinus lifts should be avoided. • Lateral window sinus lifts were not asociated with any implant failures.  • Given the high survival rates of implants, a smal sample size does not alow for trends in the data to reach statistical significant, even if a true asociation exists. 6.6 Future directions In order to more eficiently expand this investigation over time, a two-page form was developed to record al of the necesary investigation for each implant case (appendix I). The first form is to be completed at the time of implant planning and placement. The second is to be completed at the time of implant restoration and after every follow up at least one year after placement. This study can then be revisited in several years with a larger sample size and longer follow up to validate if any of the observed trends are significant. Currently, the university protocol includes a radiographic follow up each year after implant restoration for five years. 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J Oral Maxilofac Surg 62:773-780.  129 APPENDICES APENDIX A: Periodontal charting    130 APENDIX B: Surgical sumary         131 APENDIX C: Implant surgical sumary          132 APENDIX D: Post-operative sumary         133 APENDIX E: Implant guarante form          134 APENDIX F: Variables included  Data collected from patient charts:  Demongraphic data: • Date of birth/age • Sex • Gender  Health status: • Coagulopathies • Hypertension • Diabetes • Osteoporosis • Arthritis • Medications • Smoking history (current, former, never) • Pack years • Year quit • Reported bruxism  Clinical information: • Date of initial exam • Reason for tooth loss • Periodontal health status • Date of tooth extraction • Implant site • Adjacent tooth probing depth • Adjacent tooth furcation involvement • Date of stage 1 surgery • Previous socket preservation (materials used, healing time) • Previous guided bone regeneration (materials used, healing time) • Previous sinus augmentation (materials used, healing time) • Simultaneous guided bone regeneration (materials used, healing time) • Simultaneous sinus augmentation (materials used, technique, healing time) • Date of stage 2 surgery  Implant variables: • Model/brand • Surface type • Taper • Width • Length • Connection    135 Surgical variables: • Torque at placement • Bone resorption at time of placement • Bone quality • Bone vascularity • Primary stability • Healing time before stage 2 or restoration • Threads exposed at time of placement • Presence of bony dehiscence at the time of placement  Post-operative variables: • Post-operative complications (bleding, infection, paresthesia) • Post-operative chemotherapy (antibiotic, analgesic, steroid, chlorhexidine)  Prosthodontic variables: • Type of temporary restoration • Type of permanent restoration • Date of permanent restoration insertion • Post-insertion complications  Follow up information: • Date of most recent follow up  • Threads exposed at most recent follow up • Peri-implantitis treatment (date, defect, materials used) • Implant failure                 136 APENDIX G: Implant dimensions   Fig 30. Wide platform Nobel BioCare implant at 16, narow platform implant at 14, regular platform implant at 13.     Fig 31. Short (8 m) Nobel BioCare implant    Fig 32. Long (13 m) Nobel BioCare Implant  137 APENDIX H: Radiographic signs of marginal bone loss around implants  Fig. 33 Diferences in implant design betwen Nobel BioCare and Strauman implants in terms of distance from the implant neck to the first thread.        No thread exposure      Exposure of two threads on the distal of the implant at 22  138     Exposure of four threads on the mesial of the implant at 35 Fig 34. Amount of marginal bone loss around implants.  139 APENDIX I. Documentation for future cases Implant Case Documentation *please complete a form for EACH implant placed  PART 1. To be completed at stage 1 surgery  Chart number: ____________  age: _______  gender: ________  Date of stage 1 surgery: _____________ Implant replacing failed implant? ( ) yes ( ) no  Systemic disease: ( ) osteoporosis ( ) diabetes ( ) other: __________________________  Smoking status: ( ) never ( ) former ( ) current pack years: ________ year quit: ______  Date of initial implant exam: ______________  Reason for tooth loss: ( ) periodontal disease ( ) other ( ) unknown  Current periodontal diagnosis: _______________________________________________  Date of tooth extraction: ___________________  Implant site: ______  Depest probing depth and/or furcation involvement adjacent to implant site: _________  Previous surgery: ( ) socket preservation ( ) guided bone regeneration ( ) sinus augmentation (specify materials and date completed): _______________________________________________________________________  Simultaneous surgery: ( ) socket preservation ( ) guided bone regeneration ( ) sinus augmentation (specify materials): _______________________________________________________________________  Implant brand/model: _____________________________________________________  Implant surface type: ( ) SLA ( ) TiUnite ( ) other: ____________________  Implant shape: ( ) straight ( ) tapered   width: _________   length: __________  Torque: __________ Primary stability: _____________  Post-operative chemotherapy (note al agents prescribed/recommended and dosage): _______________________________________________________________________  Number of threads exposed at placement (clinical and/or radiographic): _________   140 PART 2. Post-operative and follow up information  Post-operative complications: ( ) bleding ( ) paresthesia ( ) infection ( ) other: ________  Type of provisional restoration:( ) crown ( ) denture ( ) hybrid ( ) FPD ( ) splinted crowns  Date of stage 2 surgery: ______________ Date of implant restoration: _______________  Type of permanent restoration:( ) crown ( ) denture ( ) hybrid ( ) FPD ( ) splinted crowns  Post-placement soft or hard tisue augmentation (date/type/materials used): __________ _______________________________________________________________________  Post-insertion prosthodontic complications (date/type): ___________________________ ________________________________________________________________________  ( ) Peri-implantitis ; treatment (date/type): _____________________________________ _______________________________________________________________________  (1) Date of most recent follow up:_________________  Threads exposed at most recent follow up: __________________  (2) Date of most recent follow up:_________________  Threads exposed at most recent follow up: __________________  (3) Date of most recent follow up:_________________  Threads exposed at most recent follow up: __________________  (4) Date of most recent follow up:_________________  Threads exposed at most recent follow up: __________________  (5) Date of most recent follow up:_________________  Threads exposed at most recent follow up: __________________  (6) Date of most recent follow up:_________________  Threads exposed at most recent follow up: __________________  ( ) IMPLANT FAILURE Date removed: ___________________  *please use an additional form for any replacement implant  141 APENDIX J: Ethics course certificate  

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