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Article Type : Original Article
Article Title: Survival rates and complication types for single implants provided at the Melbourne Dental School
Running title: Implant and crowns survival and complications
Authors: Q. Guo*#, R. Lalji*#, A.V. Le*, R.B. Judge*, D. Bailey*, W. Thomson*, K. Escobar* #
Co-first Author
* Melbourne Dental School (MDS), University of Melbourne, Victoria
Contact Information for Correspondence: Associate Professor Roy Judge BDS LDS RCS MDSc PhD Associate Professor (Prosthodontics) Academic Clinical Director - Melbourne Dental Clinic (MDC) Melbourne Dental School The University of Melbourne Level 2, 723 Swanston Street Melbourne Victoria 3010 Australia This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/adj.12248 This article is protected by copyright. All rights reserved.
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Tel. +61 3 9035 8446 / Fax. +61 3 9035 9797 email: [email protected] Reprints are not available from the authors.
INTRODUCTION Advances in dentistry have allowed for the development of wider treatment philosophies for the replacement of missing teeth. In many cases where adjacent teeth are unrestored or minimally restored, dental implants have become a popular treatment option due to reported success in terms of aesthetics, function and longevity, while minimising the biological cost to adjacent teeth. 1-5
A meta-analysis of 26 studies by Jung et al3 reported a 96.8% survival rate for implants supporting single crowns (referred to herein as “single implants” or simply "implants") and a 94.5% survival rate for implant-supported single crowns (ISSCs) after 5 years. Despite the reported high survival rates, various studies have identified many complications associated with implant therapy such as surgical, mechanical, aesthetic and phonetic complications, peri-implant soft tissue related complications, peri-implant bone loss and implant loss due to peri-implantitis.3, 6, 7
To date, only a limited number of studies have been conducted to investigate implant complications within teaching settings in Australia.8 The researchers have chosen to conduct such a study at the Royal Dental Hospital of Melbourne (RDHM), the largest community dental clinic in the state of Victoria. RDHM provides a wide range of dental services, including implant therapy, to those eligible for public dental care and is run by Dental Health
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Service Victoria (DHSV). RDHM provides one of the clinical facilities for the postgraduate students of Melbourne Dental School (MDS), University of Melbourne.
The aim of this paper is to gain insight into implant care provision in a teaching environment by describing and identifying (1) the demographics of public patients receiving single tooth replacement using implants at the MDS and (2) the types and incidences of implant failure and complications within this treatment group.
The results of this study can provide important reference points for clinicians in understanding complications that may arise in implant therapy, which may in turn influence treatment patterns.
MATERIALS AND METHODS To address the study aims, a retrospective cohort study design was used to review the population of patients receiving implant treatments at the RDHM. This study was approved by the DHSV Ethics Committee (Approval No. 217).
Patients who had at least one implant placed or restored at the RDHM within the study period of 1st of January 2005 to 31st of December 2009 were included in the study. Clinicians who placed and/or restored implants included postgraduate students enrolled in the Periodontics, Oral-maxillofacial surgery, Prosthodontics and the Postgraduate Diploma in Clinical Dentistry (Implants) programs, as well as RDHM staff (specialist practitioners).
An
electronic search of the hospital database (Titanium Software®, Spark Dental Technology, Australia) using relevant treatment codes identified that 1074 implants were placed during the study period. One hundred and thirty-seven implants were excluded because patient
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records were unavailable or incomplete. The remaining 937 implants were associated with single units, single tooth cantilever units or multiple units. This paper reports on the 620 implants associated with single units only.
Defined details of the implant treatments were collected from patient records. A team of postgraduate student researchers was trained and calibrated by a senior researcher experienced in clinical data collection. A data collection template was adapted from a template created for a similar concurrent study in Victorian private dental practices.
Information was collected regarding: •
Practitioner type (specialist or postgraduate student)
•
Patient demographics (age and gender)
•
Patient co-morbidities (diabetes, osteoporosis, and smoking status)
•
Implant details (site, connection type, length and diameter)
•
Surgical procedure (one-stage or two-stage)
•
Restorations (method of retention)
•
Complications
Complications For the purposes of this study, a complication was deemed to be any event that required the clinician to revisit the case other than for ongoing maintenance. All complications recorded in patient records were transcribed verbatim onto the data collection template. Due to the large array of clinical complications, they were classified into surgical, biological and restorative complication groups before further differentiation.
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Surgical complications were defined as any implant-related complications arising at the time of implant placement. They included hard tissue complications, haemorrhage, neurosensory disturbance and infection or complications with components during implant placement.
Biological complications were defined as implant-related complications arising any time after implant placement that involve soft and hard tissues around the implant site. They included integration and bone loss issues, soft tissue complications, haemorrhage, infection, pain and/or swelling (HIPS), non-restorable implants and post-placement external trauma. HIPS were further sub-divided into post-operative HIPS (within six weeks of implant placement) and HIPS (more than six weeks after implant placement).
Restorative complications were defined as any complications related to ISSCs. These were subdivided into two groups: pre-definitive restoration complications and definitive restoration complications. Pre-definitive restorative complications were those arising prior to definitive (i.e. final) restoration, including those related to healing abutment and provisional restorations. Definitive restorative complications were those related to retention, restorative hardware components, veneering materials, occlusion and aesthetics of definitive restorations.
STATISTICAL ANALYSIS All information on the data collection sheets was entered into a Microsoft® Access (Microsoft Corporation, WA, USA) database, which was created specifically for the study. The database was imported into SPSSTM Statistical Package for the Social Sciences (Version 21, SPSS Inc., Chicago, IL, USA) for analysis. Descriptive statistics and frequencies of various characteristics were used to better understand the nature of the study sample.
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Implant survival and complication occurrences were statistically expressed in terms of cumulative incidence, event rate per 100 implant-years and estimated one- and five-year implant survival and success (complication-free) rates.
Implant survival was defined as an implant remaining in-situ at the end of the study period. Any implant that did not survive during the study period was considered a failure. Implantrelated complications were recorded as individual events and counted numerically. A surviving implant with no reported complication was considered a success.
Cumulative incidence (the proportion of the study population that encountered a failure or complication over a specified period of time) was calculated by dividing the number of implant failure or complication events, as applicable, by the total number of implants over the five-year study period. Not all single implants and ISSCs had follow-ups for the full five years, as patient recruitment occurred throughout the study period. The mean follow-up time for single implants was 2.18 years. The mean follow up time for ISSCs was 2.03 years.
The event rate was defined as the incidence of complications or failures, as applicable, over the number of implant-years observed. Implant-years for a single implant was the number of years from the date of implant placement to the earlier of (i) the date of implant failure or (ii) the end of study observation (30th March 2010). Total implant-years for all implants were calculated by adding the implant-years of all implants observed. Failure and complication event rates per 100 implant-years were calculated by dividing the number of events by the total implant-years and multiplying by 100. The confidence intervals assumed a Poisson-rate distribution.
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One- and five-year estimated success rates for single implants and ISSCs were calculated using the formula: S (T) = exp (-T*event rate), where "S" denotes survival or success, "T' is time (years), "exp" is the exponential function, "event rate" is the estimated event rate per 100 implant-years. The confidence intervals for the success rates were also constructed using the confidence limits for the event rates.
All analyses assumed that all implants were
independent.
RESULTS Clinicians Postgraduate students were responsible for 90.3% of the single implant placements and 91.4% of the ISSC restorations. Specialist practitioners were responsible for the remaining placements and restorations (Fig 1).
Patients Four hundred and six patients received implant therapy to replace 620 single missing teeth. A descriptive overview of patient profile, including concurrent medical information, is given in Table 1.
At the midpoint of the study, patient ages ranged between 17 and 82 years with a median age of 44 (Fig 2).
Single implants and implant-supported single crowns Six hundred and twenty single implants were placed during the study period. Of these, 188 implants were not restored during the study period, and therefore were not included in the restorative analysis because (i) the implants were restored after 2009, (ii) the patients did not
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analysis with a focus on the association between patient, surgical and restorative variables and complications would facilitate better understanding of the causes and therefore possible preventive measures.
Acknowledgements: This study was approved by the Dental Health Services Victoria Human Research Ethics Committee (Approval No. 217) and is funded by the Melbourne Dental School Research Committee.
The authors would like to thank Dr. Angelos Sourial, Dr. Peter Apostolopoulos and Dr. Vivien Yeo for assisting with data collection, Ms. Ann Thomson for carrying out data-entry and Ms. Sandy Clarke for carrying out statistical analysis. The authors have no conflicts of interest to report in connection with this study.
References 1. Chang M, Wennstrom J, Odman P, Andersson B. Implant supported single-tooth replacements compared to contralateral natural teeth - Crown and soft tissue dimensions. Clinical Oral Implants Research 1999; 10(3): 185-194. 2. Torabinejad M, Anderson P, Bader J, Brown L, Chen L, White S, et al. Outcomes of root canal treatment and restoration, implant-supported single crowns, fixed partial dentures, and extraction without replacement: a systematic review. Journal Of Prosthetic Dentistry 2007, Oct; 98(4): 285-311. 3. Jung R, Pjetursson B, Glauser R, Zembic A, Zwahlen M, Lang N. A systematic
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An 8-Year Study of Dental Implants. Implant Dentistry 2008; 17(2): 200. 30. Jemt T, Hager P. Early Complete Failures of Fixed Implant-Supported Prostheses in the Edentulous Maxilla: A 3-Year Analysis of 17 Consecutive Cluster Failure Patients. Clinical Implant Dentistry And Related Research 2006; (2): 77. 31. Zoghbi S, de Lima L, Saraiva L, Romito G. Surgical Experience Influences 2-Stage Implant Osseointegration. Journal Of Oral And Maxillofacial Surgery 2011; 69(11): 2771-2776. 32. Lambert P, Morris H, Ochi S. Relationship Between Implant Surgical Experience and Second-Stage Failures: DICRG Interim Report No. 2. Implant Dentistry 1994; 3(2): 97.
Figure legends Fig 1. Distribution of single implant placements and ISSC restorations by clinician type. Fig 2. Distribution of patients according to age group. Fig 3. Implant connection type. Fig 4. Method of ISSC retention. Fig 5. Distribution of types of surgical complications.
Table legends Table 1. Overview of patient profile Table 2: Cross-tabulation of surgical and restorative status Table 3. Implant failure rates Table 4. Types of hard tissue surgical complications Table 5. Biological complications Table 6: Restorative complications
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Table 7. Restorative complications Total events/
Event rate per 100 Cumulative
Restorative complications
total
implant years estimate incidence %
implants Pre-definitive
restorative
(CI 95%)
32/451
7.1
3.53 (2.41-4.98)
Retention
22/444
5.0
2.44 (1.53-3.70)
Screw/abutment
17/444
3.8
1.89 (1.10-3.02)
Occlusion
11/444
2.5
1.22 (0.61-2.19)
Aesthetics
8/444
1.8
0.89 (0.38-1.75)
Veneer
5/444
1.1
0.56 (0.18-1.30)
Total*
63/444
14.2
7 (5.38-8.95)
complication
* Excluding pre-definitive restorative complications.
Fig 1. Distribution of single implant placements and ISSC restorations by clinician type.
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Restorative complications As explained previously, restorative complications were divided into two groups, predefinitive and definitive, for analysis. Pre-definitive restorative complication analysis was only performed on implants that were either provisionally (seven implants) or definitively restored (444 implants) during the study period.
Thus the pre-definitive restorative
complication group comprised a total of 451 implants. Only the 444 implants that were definitively restored during the study period were included in the definitive restorative complication group.
Pre-definitive restorative complications In the 451 implants studied in this group, 32 pre-definitive restoration complications were reported in 27 implants, yielding a cumulative pre-definitive restorative complication incidence of 7.1%. Twenty three implants had one complication, three implants had two complications and one implant had three complications. Of the 32 pre-definitive restoration complications, there were 23 (71.9%) healing abutment complications, six (18.7%) procedural complications, and three (9.4%) provisional prosthesis complications.
The estimated event rate for pre-definitive restorative complications was 3.53 per 100 implant-years.
Definitive restorative complications In the 444 implants studied in this group, sixty three definitive restoration complications were reported in 59 implants, giving a cumulative definitive restorative complication incidence of 14.2%.
One restorative complication was recorded in 55 implants and two restorative
complications were recorded in four implants.
The most frequent definitive restorative
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complication was retention-related (22 events, or 34.9%), which included 16 loose crowns with no recorded cause and six events of screw access issues.
Screw loosening and abutment complications accounted for 17 cases (27.0%) of the total definitive restorative complications reported. Of these 17 complication events, there were five cross-pin screw loosening, three cross-pin screw fractures, two abutment or prosthetic screw loosening, two screw head or thread damage and five unspecified loose crowns. No abutment or prosthetic screw fracture was reported.
Other restoration complications such as occlusion and wear issues (11 events, or 17.5%), aesthetic issues (8 events, or 12. 7%), veneer chipping and fracture issues (5 events, or 7.9%) were relatively few in number. The estimated definitive restorative complication rates ranged from 0.56 (veneer complications) to 2.44 (retention complications) per 100 implant-years (Table 6).
DISCUSSION The aim of this five-year retrospective cohort study was to gain insight into dental implant care provision by MDS clinicians at the RDHM. This paper focused on the survival rates, types and occurrences of complications for single implants and ISSCs in this postgraduate teaching environment.
Of the 422 patients who received implant therapy during the study period, the vast majority were female (70.2%) and non-smokers (69.2%). A significant proportion of patients were smokers and former smokers (17.0% and 12.3%, respectively). At the midpoint of the study, the median age was 44 years, with the largest proportion of patients falling into the 41-50
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year age group (26.8%) followed by roughly similar proportions of patients in the 31-40 and 51-60 year age groups (17.3% and 16.6%, respectively). 14.7% of patients were in the 21-30 year age group compared to 11.1% in the 61-70 year age group. It is important to note that the patients included in this report were those that received single implants. If implants supporting multi-unit prostheses were included in the analysis, it is probable that a higher proportion of patients in the older age group brackets would have been observed.
This study showed a cumulative implant failure rate of 2.7% and a corresponding implant survival rate of 97.3%, yielding estimated single implant survival rates of 98.8% at 1 year and 93.9% at 5 years. This was not appreciably different from other studies conducted in a similar teaching environment.8-11 Although the single implant survival rate was high, a biological complication cumulative incidence of 17.6% and a definitive restorative complication cumulative incidence of 14.1% was found over the five-year study period.
The most frequently recorded complication at the time of surgery was hard tissue-related, occurring in 10.1% of the 622 implant surgeries. These complications included fenestrations, dehiscences, perforation of the bony plate and maxillary sinus involvement. An increased incidence of surgical complications has been found to be associated with incorrect surgical techniques22 by inexperienced surgeons.23 Since postgraduate students were responsible for 90.3% of the single implant placements in this study, the operator's level of experience may have influenced the number of surgical complications.
This study estimated that 33.2% of implants were expected to have at least one biological complication after 5 years. The most frequently observed biological complication after implant placement was soft tissue-related, with an estimated rate of 13.7% after 5 years. This
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is in keeping with Jung et al18 (9.7% after 5 years). Soft tissue complications such as periimplant mucositis, gingival overgrowth and recession, arise from the inflammatory host response to the biofilm formation at the trans-mucosal zone around implants.12 Ensuring the restoration allows for optimal oral hygiene can reduce soft tissue complications.
Integration and bone loss complications were almost as frequently observed as soft tissue complications, with an estimated rate of 12.1% after 5 years. Osseointegration and bone loss issues may have been influenced by local site factors such as poor bone quality and/or inadequate quantity, hard tissue-related surgical complications encountered during time of implant placement (bony dehiscences and/or fenestrations) or possible inadequate surgical technique by the inexperienced operators. Surgical experience and the effect of the learning curve has been reported to influence the osseointegration of dental implants, with a higher osseointegration rate reported in implants placed by experienced clinicians compared to inexperienced operators (94.4% vs. 84.0%).32 Lambert et al33 reported that implants placed by inexperienced operators for example students (that performed less than 50 implant procedures) were more than twice as likely to fail compared to those implants placed by experienced clinicians (that placed more than 50 implants).
This study showed a cumulative pre-definitive restorative complication incidence of 7.1%, with the most common restorative complication observed during the pre-definitive restoration phase being healing abutment loss or loosening (23 events from 451 implants).
The
cumulative definitive restorative complication incidence was 14.2%, within which screw and abutment loosening, which comprised 27.0% of all definitive restorative complications, had a cumulative incidence of 3.8%. Abutment screw loosening in ISSCs has been widely reported in clinical studies and systematic reviews.3,6,7 Jung et al reported a screw and abutment
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loosening incidence of 8.8%3 and 5.8%, respectively.18 The 3.8% screw and abutment loosening incidence rate reported in this study did not include 27 cases of crown loosening which had no cause description. It is probable that a screw, abutment or cross-pin related issue could have caused crown loosening. Restorative screws used to retain an implant crown can loosen for many reasons including (i) screw joint relaxation, (ii) inadequate passive fit, (iii) poor component fit, and (iv) excessive loading of the screw joint.17 After including the 27 cases of loose crowns into the number of abutment and screw complication events, the cumulative incidence of abutment and screw loosening was 9.9%, which is closer to the incidence rate reported by Jung et al.3 Patients who did not return for follow-ups may have influenced the low rate reported here, as many may have returned to their referring dentists for further dental care, or a change in their public health eligibility status may have resulted in their seeking private dental care.
The majority (93.5%) of the ISSCs in this cohort were screw-retained, which was consistent with the philosophy of restoration retrievability amongst prosthodontists across Australia.19 While some studies20,21 found no significant difference between cement- and screw-retained restorations with regards to implant survival or crown loss; advocates of screw retention22, 23 emphasize retrievability for ease of managing technical complications such as porcelain fracture, occlusion adjustment, contact point correction and aesthetic discrepancies.
Multiple studies3, 18, 24, 25 have identified a wide range of complications with implant therapy. Comparison of studies can be difficult as diagnostic parameters are not standardized and the definitions of success, survival and complications often vary. Statistical analysis used for complication reporting amongst researchers was also inconsistent, including the use of terms such as “annual rate”, “cumulative incidence”, “cumulative complication rate”, “estimated
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complication-free rate” and “complication rate per 100 implant-years estimate”.
In a
systematic review by Berglundh et al25, biological and technical complications were considered in only 40 to 60% and 60 to 80% of the studies, respectively. Goodacre et al7 concluded that “it was not possible to calculate an overall complications incidence for implant prostheses because there were no multiple clinical studies that evaluated all or most of the categories of complications”. Such observations suggest that the incidence of implantrelated complications may be under-estimated and should be interpreted with caution.
There are inconsistencies in the reporting of implant-related complications among researchers. Goodacre et al26 defined an implant complication as “a secondary condition that developed during or after implant surgery or prosthesis placement”. They also stated that the occurrence of a complication did not necessarily indicate that sub-standard dental care was provided nor did it necessarily mean clinical failure. Understanding that complications in implant dentistry do occur is important for both the clinician and patient, and is a key rationale for maintenance, which has been suggested to be every three or four months in the first year, then yearly afterwards.27,
28, 29
Clinicians may consider informing patients of
potential complications during the treatment planning stage to manage patient expectations and minimise patient dissatisfaction with future adverse outcomes.
Certain biases and limitations exist in this study which may have influenced the results. The mean follow-up time was short, being 2.18 years for single implants and 2.03 years for ISSCs, whereas a mean follow-up time of at least five years is common in most systematic reviews.3, 18 The number and type of complications may be under-reported due to loss of follow-up of patients who returned to their referring dentists for further care. The MDS’s teaching philosophy encourages a one-stage surgical placement of implants, no immediate
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loading of implants and screw-retained restorations for retrievability. These philosophies have predetermined data collection regarding two-stage placement of implants, immediate loading of implants and cemented ISSC designs.
All analyses assumed that implant
complications and/or failures occurred independently. Other studies30,
31
have identified
possible clustering effects (i.e. more than one implant failure per patient, not necessarily in the same area or quadrant) for implants and ISSCs.
These clustering effects were not
included in the analysis to facilitate a direct comparison of results with other studies that did not perform cluster modelling.
During data collection, treatment details were not always clearly recorded in patient records. Information such as methods of osseointegration assessment, baseline and progressive radiographic assessment, periodontal probing depths around implants at periodic review visits, restorative details (abutment types and materials), implant identification and management of complications were sometimes unclear. Incomplete or unclear records in retrospective studies may have resulted in an under-representation of complication occurrences.
Accurate and detailed records can improve quality patient care and inter-
clinician consistency in all clinical areas, and in teaching environments such as MDS where dental care is provided by multiple clinicians.
Conclusion Single tooth replacement with implant therapy within a teaching environment has high survival rates for both the implant and the single crown. However, complications do arise and this fact should be communicated clearly to the patient from the outset.
The
understanding that implant therapy is not complication-free emphasises the importance of ongoing maintenance. This paper only described the occurrences of complications; further
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analysis with a focus on the association between patient, surgical and restorative variables and complications would facilitate better understanding of the causes and therefore possible preventive measures.
Acknowledgements: This study was approved by the Dental Health Services Victoria Human Research Ethics Committee (Approval No. 217) and is funded by the Melbourne Dental School Research Committee.
The authors would like to thank Dr. Angelos Sourial, Dr. Peter Apostolopoulos and Dr. Vivien Yeo for assisting with data collection, Ms. Ann Thomson for carrying out data-entry and Ms. Sandy Clarke for carrying out statistical analysis. The authors have no conflicts of interest to report in connection with this study.
References 1. Chang M, Wennstrom J, Odman P, Andersson B. Implant supported single-tooth replacements compared to contralateral natural teeth - Crown and soft tissue dimensions. Clinical Oral Implants Research 1999; 10(3): 185-194. 2. Torabinejad M, Anderson P, Bader J, Brown L, Chen L, White S, et al. Outcomes of root canal treatment and restoration, implant-supported single crowns, fixed partial dentures, and extraction without replacement: a systematic review. Journal Of Prosthetic Dentistry 2007, Oct; 98(4): 285-311. 3. Jung R, Pjetursson B, Glauser R, Zembic A, Zwahlen M, Lang N. A systematic
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review of the 5-year survival and complication rates of implant-supported single crowns. Clinical Oral Implants Research 2008; 19(2): 119-130. 4. Pjetursson B, Lang N. Prosthetic treatment planning on the basis of scientific evidence. Journal Of Oral Rehabilitation 2008; 3572-79 5. Zitzmann N, Krastl G, Hecker H, Walter C, Weiger R. Endodontics or implants? A review of decisive criteria and guidelines for single tooth restorations and full arch reconstructions. International Endodontic Journal 2009; 42(9): 757-774. 6. Pjetursson B, Brägger U, Lang N, Zwahlen M. Comparison of survival and complication rates of tooth-supported fixed dental prostheses (FDPs) and implantsupported FDPs and single crowns (SCs). Clinical Oral Implants Research 2007; 18 Suppl 397-113. 7. Goodacre C, Bernal G, Rungcharassaeng K, Kan J. Clinical Complications with Implants and Implant Prostheses. Oral Health 2003; 9438-48. 8. Smith L, Ng M, Grubor D, Chandu A. Outcomes of dental implants placed in a surgical training programme. Australian Dental Journal 2009; 54(4): 361-367. 9. Barias P, Lee D, Judy Chia-Chun Y, Sukotjo C, Campbell S, Knoernschild K. Retrospective Analysis of Dental Implants Placed and Restored by Advanced Prosthodontic Residents. Journal Of Prosthodontics 2013; 157. 10. Chung W, Rubenstein J, Phillips K, Raigrodski A. Outcomes assessment of patients treated with osseointegrated dental implants at the University of Washington Graduate Prosthodontic Program, 1988 to 2000. International Journal Of Oral & Maxillofacial Implants 2009; 24(5): 927-935. 11. Starr C, Maksoud M. Implant treatment in an urban general dentistry residency program: a 7-year retrospective study. The Journal Of Oral Implantology 2006; 32(3): 142-147.
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12. Lang N, Wilson T, Corbet E. Biological complications with dental implants: their prevention, diagnosis and treatment. Clinical Oral Implants Research 2000; 11 Suppl 1146-155. 13. Edelhoff D, Spiekermann D, Yildirim M. A review of esthetic pontic design options. Quintessence International 2002; 33(10): 736-746. 14. Wagman S. The role of coronal contour in gingival health. The Journal Of Prosthetic Dentistry 1977; 37(3): 280-287. 15.
Papaioannou W, Quirynen M, Nys M, van Steenberghe D. The effect of periodontal parameters on the subgingival microbiota around implants. Clinical Oral Implants Research 1995; 6(4): 197-204.
16. Loe H, Theilade E, Jensen S. Experimental gingivitis in man. The Journal Of Periodontology 1965; 36177-187. 17. Gervais M, Hatzipanagiotis P, Wilson P. Cross-pinning: the philosophy of retrievability applied practically to fixed, implant-supported prostheses. Australian Dental Journal 2008; 53(1): 74-82. 18. Jung R, Zembic A, Pjetursson B, Zwahlen M, Thoma D. Systematic review of the survival rate and the incidence of biological, technical, and aesthetic complications of single crowns on implants reported in longitudinal studies with a mean follow-up of 5 years. Clinical Oral Implants Research 2012; 232-21. 19. Sambrook R, Judge R, Abuzaar M. Strategies for restoration of single implants and use of cross-pin retained restorations by Australian prosthodontists. Australian Dental Journal 2012; 57(4): 409-414. 20. Sherif S, Susarla H, Kapos T, Munoz D, Chang B, Wright R. A Systematic Review of Screw- versus Cement-Retained Implant-Supported Fixed Restorations. Journal Of Prosthodontics-Implant Esthetic And Reconstructive Dentistry 2013; 23(1): 1-9.
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21. Weber H, Sukotjo C. Does the type of implant prosthesis affect outcomes in the partially edentulous patient?. International Journal Of Oral & Maxillofacial Implants 2008; 22140-170. Sailer I, Muhlemann S, Zwahlen M, Hammerle C, Schneider D. Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clinical Oral Implants Research 2012; 23163-201. 22. Weber H, Kim D, Ng M, Hwang J, Fiorellini J. Peri-implant soft-tissue health surrounding cement- and screw-retained implant restorations: a multi-center, 3-year prospective study. Clinical Oral Implants Research 2006; 17(4): 375-379. 23. Simonis P, Dufour T, Tenenbaum H. Long-term implant survival and success: a 1016-year follow-up of non-submerged dental implants. Clinical Oral Implants Research 2010; 21(7): 772-777. 24. Berglundh T, Persson L, Klinge B. A systematic review of the incidence of biological and technical complications in implant dentistry reported in prospective longitudinal studies of at least 5 years. Journal Of Clinical Periodontology 2002; 29197-212. 25. Goodacre C, Kan J, Rungcharassaeng K. Clinical complications of osseointegrated implants. The Journal Of Prosthetic Dentistry 1999; (5): 537. 26. Chen S, Darby I. Dental implants: Maintenance, care and treatment of peri-implant infection. Australian Dental Journal 2003; 48(4): 212-220. 27. Todescan S, Lavigne S, Kelekis-Cholakis A. Guidance for the Maintenance Care of Dental Implants: Clinical Review. Journal Of The Canadian Dental Association 2012; 78 28. The British Society of Prothodontics. Guidelines on standards for the treatment of patients
using
endosseous
implants.
URL:‘http://www.bsspd.org/About/BSSPD+guidelines.aspx’. Accessed June 2014 29. Schwartz-Arad D, Laviv A, Levin L. Failure Causes, Timing, and Cluster Behavior:
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An 8-Year Study of Dental Implants. Implant Dentistry 2008; 17(2): 200. 30. Jemt T, Hager P. Early Complete Failures of Fixed Implant-Supported Prostheses in the Edentulous Maxilla: A 3-Year Analysis of 17 Consecutive Cluster Failure Patients. Clinical Implant Dentistry And Related Research 2006; (2): 77. 31. Zoghbi S, de Lima L, Saraiva L, Romito G. Surgical Experience Influences 2-Stage Implant Osseointegration. Journal Of Oral And Maxillofacial Surgery 2011; 69(11): 2771-2776. 32. Lambert P, Morris H, Ochi S. Relationship Between Implant Surgical Experience and Second-Stage Failures: DICRG Interim Report No. 2. Implant Dentistry 1994; 3(2): 97.
Figure legends Fig 1. Distribution of single implant placements and ISSC restorations by clinician type. Fig 2. Distribution of patients according to age group. Fig 3. Implant connection type. Fig 4. Method of ISSC retention. Fig 5. Distribution of types of surgical complications.
Table legends Table 1. Overview of patient profile Table 2: Cross-tabulation of surgical and restorative status Table 3. Implant failure rates Table 4. Types of hard tissue surgical complications Table 5. Biological complications Table 6: Restorative complications
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Abbreviations and acronyms: DTF= Direct to fixture HIPS = haemorrhage, infection, pain and/or swelling ISSCs = Implant-supported single crowns MDS = Melbourne Dental School RDHM = Royal Dental Hospital of Melbourne SPSS = Statistical Package for the Social Sciences
Table 1. Overview of patient profile Categories
Descriptions
N (%)
Gender
Male
121 (29.8)
Female
285 (70.2)
Diabetes
Yes
24 (5.9)
Osteoporosis/Osteopenia
Yes
6 (1.5)
Tooth wear
Yes
134 (33.0)
Smoking status
Smoker
69 (17.0)
Previous Smoker
50 (12.3)
Non-smoker
281 (69.2)
Not Recorded
6 (1.5)
Table 2: Cross-tabulation of surgical and restorative status Definitive Restorative Analysis
Total
Included
Excluded
Included
432
188
620
Excluded
12
0
12
444
188
632
Surgical analysis
Total
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Table 3. Cross-tabulation of method of restoration retention, implant region and implant platform. Implant Region Implant Method of Retention Platform Anterior Posterior Direct-to-fixture (n=107) (24.1%) 50 (46.7%) 57 (53.3%) Cross-pin (n= 120) (27.0%) 50 (66.7%) 40 (33.3%) Cement (n=5) (1.1%) 5 (100%) 0 Bone Level Not Recorded (n=5) (1.8%) 5 (62.5%) 3 (37.5%) Total (n=240) (54.1%) 140 (58.3%) 100 (41.7%) Direct-to-fixture (n=155) (34.9%) Cross-pin (n=33) (7.4%) Tissue Level Cement (n=9) (2.0%) Not Recorded (n=7) (1.6%) Total (n=204) (45.9%)
Total
Direct-to-fixture (n=262) (59.0%) Cross-pin (n=153) (34.5%) Cement (n=14) (3.2%) Not Recorded (n=15) (3.4%) Total (n=444)
8 (5.2%) 7 (21.2%) 0 0 15 (7.4%)
147 (94.8%) 26 (78.8%) 9 (100%) 7 (100%) 189 (92.6%)
58 (22.1%) 87 (56.9%) 5 (35.7%) 5 (33.3%) 155 (34.9%)
204 (77.9%) 66 (43.1%) 9 (64.3%) 10 (66.7%) 289 (65.1%)
Table 4. Implant failure rate
Total failures/ Total implant surgeries
Cumulative incidence %
Rate per 100 implant years estimate (CI 95%)
17/622
2.7
1.26 (0.73 – 2.01)
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Table 5. Types of hard tissue surgical complications Hard tissue complication type
N
Primary stability not obtained
20
Fenestration/dehiscence
14
Unexpected sinus involvement
11
Insufficient bone
10
Angulation error
5
Trauma to adjacent tooth
3
Total
63
Table 6. Biological complications
Biological
Total events/
Cumulative
Event rate per 100 implant years
complication
total implants
incidence %
estimate (CI 95%)
Soft tissue
40/620
6.5
2.96 (2.11-4.03)
Integration/bone
35/620
5.6
2.59 (1.80-3.60)
HIPS
25/620
4.0
1.85 (1.20-2.73)
Post-op HIPS
8/620
1.3
0.59 (0.26-1.17)
Post-op external
1/620
0.2
0.07 (0-0.41)
109/620
17.6
8.06 (6.62-9.72)
loss
trauma Total
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Table 7. Restorative complications Total events/
Event rate per 100 Cumulative
Restorative complications
total
implant years estimate incidence %
implants Pre-definitive
restorative
(CI 95%)
32/451
7.1
3.53 (2.41-4.98)
Retention
22/444
5.0
2.44 (1.53-3.70)
Screw/abutment
17/444
3.8
1.89 (1.10-3.02)
Occlusion
11/444
2.5
1.22 (0.61-2.19)
Aesthetics
8/444
1.8
0.89 (0.38-1.75)
Veneer
5/444
1.1
0.56 (0.18-1.30)
Total*
63/444
14.2
7 (5.38-8.95)
complication
* Excluding pre-definitive restorative complications.
Fig 1. Distribution of single implant placements and ISSC restorations by clinician type.
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300
261
250
Number of implants
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Fig 2. Distribution of patients according to age group.
184
200 150
146 Tissue Level
100 50
Bone Level 15
14
0 Internal External Not Recorded Connection Connection Implant connection type
Fig 3. Implant connection type.
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Fig 4. Method of ISSC retention.
Fig 5. Distribution of types of surgical complications.
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Article Type : Original Article
Article Title: Survival rates and complication types for single implants provided at the Melbourne Dental School
Running title: Implant and crowns survival and complications
Authors: Q. Guo*#, R. Lalji*#, A.V. Le*, R.B. Judge*, D. Bailey*, W. Thomson*, K. Escobar* #
Co-first Author
* Melbourne Dental School (MDS), University of Melbourne, Victoria
Contact Information for Correspondence: Associate Professor Roy Judge BDS LDS RCS MDSc PhD Associate Professor (Prosthodontics) Academic Clinical Director - Melbourne Dental Clinic (MDC) Melbourne Dental School The University of Melbourne Level 2, 723 Swanston Street Melbourne Victoria 3010 Australia This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/adj.12248 This article is protected by copyright. All rights reserved.
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Tel. +61 3 9035 8446 / Fax. +61 3 9035 9797 email: [email protected] Reprints are not available from the authors.
INTRODUCTION Advances in dentistry have allowed for the development of wider treatment philosophies for the replacement of missing teeth. In many cases where adjacent teeth are unrestored or minimally restored, dental implants have become a popular treatment option due to reported success in terms of aesthetics, function and longevity, while minimising the biological cost to adjacent teeth. 1-5
A meta-analysis of 26 studies by Jung et al3 reported a 96.8% survival rate for implants supporting single crowns (referred to herein as “single implants” or simply "implants") and a 94.5% survival rate for implant-supported single crowns (ISSCs) after 5 years. Despite the reported high survival rates, various studies have identified many complications associated with implant therapy such as surgical, mechanical, aesthetic and phonetic complications, peri-implant soft tissue related complications, peri-implant bone loss and implant loss due to peri-implantitis.3, 6, 7
To date, only a limited number of studies have been conducted to investigate implant complications within teaching settings in Australia.8 The researchers have chosen to conduct such a study at the Royal Dental Hospital of Melbourne (RDHM), the largest community dental clinic in the state of Victoria. RDHM provides a wide range of dental services, including implant therapy, to those eligible for public dental care and is run by Dental Health
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Service Victoria (DHSV). RDHM provides one of the clinical facilities for the postgraduate students of Melbourne Dental School (MDS), University of Melbourne.
The aim of this paper is to gain insight into implant care provision in a teaching environment by describing and identifying (1) the demographics of public patients receiving single tooth replacement using implants at the MDS and (2) the types and incidences of implant failure and complications within this treatment group.
The results of this study can provide important reference points for clinicians in understanding complications that may arise in implant therapy, which may in turn influence treatment patterns.
MATERIALS AND METHODS To address the study aims, a retrospective cohort study design was used to review the population of patients receiving implant treatments at the RDHM. This study was approved by the DHSV Ethics Committee (Approval No. 217).
Patients who had at least one implant placed or restored at the RDHM within the study period of 1st of January 2005 to 31st of December 2009 were included in the study. Clinicians who placed and/or restored implants included postgraduate students enrolled in the Periodontics, Oral-maxillofacial surgery, Prosthodontics and the Postgraduate Diploma in Clinical Dentistry (Implants) programs, as well as RDHM staff (specialist practitioners).
An
electronic search of the hospital database (Titanium Software®, Spark Dental Technology, Australia) using relevant treatment codes identified that 1074 implants were placed during the study period. One hundred and thirty-seven implants were excluded because patient
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records were unavailable or incomplete. The remaining 937 implants were associated with single units, single tooth cantilever units or multiple units. This paper reports on the 620 implants associated with single units only.
Defined details of the implant treatments were collected from patient records. A team of postgraduate student researchers was trained and calibrated by a senior researcher experienced in clinical data collection. A data collection template was adapted from a template created for a similar concurrent study in Victorian private dental practices.
Information was collected regarding: •
Practitioner type (specialist or postgraduate student)
•
Patient demographics (age and gender)
•
Patient co-morbidities (diabetes, osteoporosis, and smoking status)
•
Implant details (site, connection type, length and diameter)
•
Surgical procedure (one-stage or two-stage)
•
Restorations (method of retention)
•
Complications
Complications For the purposes of this study, a complication was deemed to be any event that required the clinician to revisit the case other than for ongoing maintenance. All complications recorded in patient records were transcribed verbatim onto the data collection template. Due to the large array of clinical complications, they were classified into surgical, biological and restorative complication groups before further differentiation.
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Surgical complications were defined as any implant-related complications arising at the time of implant placement. They included hard tissue complications, haemorrhage, neurosensory disturbance and infection or complications with components during implant placement.
Biological complications were defined as implant-related complications arising any time after implant placement that involve soft and hard tissues around the implant site. They included integration and bone loss issues, soft tissue complications, haemorrhage, infection, pain and/or swelling (HIPS), non-restorable implants and post-placement external trauma. HIPS were further sub-divided into post-operative HIPS (within six weeks of implant placement) and HIPS (more than six weeks after implant placement).
Restorative complications were defined as any complications related to ISSCs. These were subdivided into two groups: pre-definitive restoration complications and definitive restoration complications. Pre-definitive restorative complications were those arising prior to definitive (i.e. final) restoration, including those related to healing abutment and provisional restorations. Definitive restorative complications were those related to retention, restorative hardware components, veneering materials, occlusion and aesthetics of definitive restorations.
STATISTICAL ANALYSIS All information on the data collection sheets was entered into a Microsoft® Access (Microsoft Corporation, WA, USA) database, which was created specifically for the study. The database was imported into SPSSTM Statistical Package for the Social Sciences (Version 21, SPSS Inc., Chicago, IL, USA) for analysis. Descriptive statistics and frequencies of various characteristics were used to better understand the nature of the study sample.
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Implant survival and complication occurrences were statistically expressed in terms of cumulative incidence, event rate per 100 implant-years and estimated one- and five-year implant survival and success (complication-free) rates.
Implant survival was defined as an implant remaining in-situ at the end of the study period. Any implant that did not survive during the study period was considered a failure. Implantrelated complications were recorded as individual events and counted numerically. A surviving implant with no reported complication was considered a success.
Cumulative incidence (the proportion of the study population that encountered a failure or complication over a specified period of time) was calculated by dividing the number of implant failure or complication events, as applicable, by the total number of implants over the five-year study period. Not all single implants and ISSCs had follow-ups for the full five years, as patient recruitment occurred throughout the study period. The mean follow-up time for single implants was 2.18 years. The mean follow up time for ISSCs was 2.03 years.
The event rate was defined as the incidence of complications or failures, as applicable, over the number of implant-years observed. Implant-years for a single implant was the number of years from the date of implant placement to the earlier of (i) the date of implant failure or (ii) the end of study observation (30th March 2010). Total implant-years for all implants were calculated by adding the implant-years of all implants observed. Failure and complication event rates per 100 implant-years were calculated by dividing the number of events by the total implant-years and multiplying by 100. The confidence intervals assumed a Poisson-rate distribution.
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One- and five-year estimated success rates for single implants and ISSCs were calculated using the formula: S (T) = exp (-T*event rate), where "S" denotes survival or success, "T' is time (years), "exp" is the exponential function, "event rate" is the estimated event rate per 100 implant-years. The confidence intervals for the success rates were also constructed using the confidence limits for the event rates.
All analyses assumed that all implants were
independent.
RESULTS Clinicians Postgraduate students were responsible for 90.3% of the single implant placements and 91.4% of the ISSC restorations. Specialist practitioners were responsible for the remaining placements and restorations (Fig 1).
Patients Four hundred and six patients received implant therapy to replace 620 single missing teeth. A descriptive overview of patient profile, including concurrent medical information, is given in Table 1.
At the midpoint of the study, patient ages ranged between 17 and 82 years with a median age of 44 (Fig 2).
Single implants and implant-supported single crowns Six hundred and twenty single implants were placed during the study period. Of these, 188 implants were not restored during the study period, and therefore were not included in the restorative analysis because (i) the implants were restored after 2009, (ii) the patients did not
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analysis with a focus on the association between patient, surgical and restorative variables and complications would facilitate better understanding of the causes and therefore possible preventive measures.
Acknowledgements: This study was approved by the Dental Health Services Victoria Human Research Ethics Committee (Approval No. 217) and is funded by the Melbourne Dental School Research Committee.
The authors would like to thank Dr. Angelos Sourial, Dr. Peter Apostolopoulos and Dr. Vivien Yeo for assisting with data collection, Ms. Ann Thomson for carrying out data-entry and Ms. Sandy Clarke for carrying out statistical analysis. The authors have no conflicts of interest to report in connection with this study.
References 1. Chang M, Wennstrom J, Odman P, Andersson B. Implant supported single-tooth replacements compared to contralateral natural teeth - Crown and soft tissue dimensions. Clinical Oral Implants Research 1999; 10(3): 185-194. 2. Torabinejad M, Anderson P, Bader J, Brown L, Chen L, White S, et al. Outcomes of root canal treatment and restoration, implant-supported single crowns, fixed partial dentures, and extraction without replacement: a systematic review. Journal Of Prosthetic Dentistry 2007, Oct; 98(4): 285-311. 3. Jung R, Pjetursson B, Glauser R, Zembic A, Zwahlen M, Lang N. A systematic
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An 8-Year Study of Dental Implants. Implant Dentistry 2008; 17(2): 200. 30. Jemt T, Hager P. Early Complete Failures of Fixed Implant-Supported Prostheses in the Edentulous Maxilla: A 3-Year Analysis of 17 Consecutive Cluster Failure Patients. Clinical Implant Dentistry And Related Research 2006; (2): 77. 31. Zoghbi S, de Lima L, Saraiva L, Romito G. Surgical Experience Influences 2-Stage Implant Osseointegration. Journal Of Oral And Maxillofacial Surgery 2011; 69(11): 2771-2776. 32. Lambert P, Morris H, Ochi S. Relationship Between Implant Surgical Experience and Second-Stage Failures: DICRG Interim Report No. 2. Implant Dentistry 1994; 3(2): 97.
Figure legends Fig 1. Distribution of single implant placements and ISSC restorations by clinician type. Fig 2. Distribution of patients according to age group. Fig 3. Implant connection type. Fig 4. Method of ISSC retention. Fig 5. Distribution of types of surgical complications.
Table legends Table 1. Overview of patient profile Table 2: Cross-tabulation of surgical and restorative status Table 3. Implant failure rates Table 4. Types of hard tissue surgical complications Table 5. Biological complications Table 6: Restorative complications
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Table 7. Restorative complications Total events/
Event rate per 100 Cumulative
Restorative complications
total
implant years estimate incidence %
implants Pre-definitive
restorative
(CI 95%)
32/451
7.1
3.53 (2.41-4.98)
Retention
22/444
5.0
2.44 (1.53-3.70)
Screw/abutment
17/444
3.8
1.89 (1.10-3.02)
Occlusion
11/444
2.5
1.22 (0.61-2.19)
Aesthetics
8/444
1.8
0.89 (0.38-1.75)
Veneer
5/444
1.1
0.56 (0.18-1.30)
Total*
63/444
14.2
7 (5.38-8.95)
complication
* Excluding pre-definitive restorative complications.
Fig 1. Distribution of single implant placements and ISSC restorations by clinician type.
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Restorative complications As explained previously, restorative complications were divided into two groups, predefinitive and definitive, for analysis. Pre-definitive restorative complication analysis was only performed on implants that were either provisionally (seven implants) or definitively restored (444 implants) during the study period.
Thus the pre-definitive restorative
complication group comprised a total of 451 implants. Only the 444 implants that were definitively restored during the study period were included in the definitive restorative complication group.
Pre-definitive restorative complications In the 451 implants studied in this group, 32 pre-definitive restoration complications were reported in 27 implants, yielding a cumulative pre-definitive restorative complication incidence of 7.1%. Twenty three implants had one complication, three implants had two complications and one implant had three complications. Of the 32 pre-definitive restoration complications, there were 23 (71.9%) healing abutment complications, six (18.7%) procedural complications, and three (9.4%) provisional prosthesis complications.
The estimated event rate for pre-definitive restorative complications was 3.53 per 100 implant-years.
Definitive restorative complications In the 444 implants studied in this group, sixty three definitive restoration complications were reported in 59 implants, giving a cumulative definitive restorative complication incidence of 14.2%.
One restorative complication was recorded in 55 implants and two restorative
complications were recorded in four implants.
The most frequent definitive restorative
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complication was retention-related (22 events, or 34.9%), which included 16 loose crowns with no recorded cause and six events of screw access issues.
Screw loosening and abutment complications accounted for 17 cases (27.0%) of the total definitive restorative complications reported. Of these 17 complication events, there were five cross-pin screw loosening, three cross-pin screw fractures, two abutment or prosthetic screw loosening, two screw head or thread damage and five unspecified loose crowns. No abutment or prosthetic screw fracture was reported.
Other restoration complications such as occlusion and wear issues (11 events, or 17.5%), aesthetic issues (8 events, or 12. 7%), veneer chipping and fracture issues (5 events, or 7.9%) were relatively few in number. The estimated definitive restorative complication rates ranged from 0.56 (veneer complications) to 2.44 (retention complications) per 100 implant-years (Table 6).
DISCUSSION The aim of this five-year retrospective cohort study was to gain insight into dental implant care provision by MDS clinicians at the RDHM. This paper focused on the survival rates, types and occurrences of complications for single implants and ISSCs in this postgraduate teaching environment.
Of the 422 patients who received implant therapy during the study period, the vast majority were female (70.2%) and non-smokers (69.2%). A significant proportion of patients were smokers and former smokers (17.0% and 12.3%, respectively). At the midpoint of the study, the median age was 44 years, with the largest proportion of patients falling into the 41-50
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year age group (26.8%) followed by roughly similar proportions of patients in the 31-40 and 51-60 year age groups (17.3% and 16.6%, respectively). 14.7% of patients were in the 21-30 year age group compared to 11.1% in the 61-70 year age group. It is important to note that the patients included in this report were those that received single implants. If implants supporting multi-unit prostheses were included in the analysis, it is probable that a higher proportion of patients in the older age group brackets would have been observed.
This study showed a cumulative implant failure rate of 2.7% and a corresponding implant survival rate of 97.3%, yielding estimated single implant survival rates of 98.8% at 1 year and 93.9% at 5 years. This was not appreciably different from other studies conducted in a similar teaching environment.8-11 Although the single implant survival rate was high, a biological complication cumulative incidence of 17.6% and a definitive restorative complication cumulative incidence of 14.1% was found over the five-year study period.
The most frequently recorded complication at the time of surgery was hard tissue-related, occurring in 10.1% of the 622 implant surgeries. These complications included fenestrations, dehiscences, perforation of the bony plate and maxillary sinus involvement. An increased incidence of surgical complications has been found to be associated with incorrect surgical techniques22 by inexperienced surgeons.23 Since postgraduate students were responsible for 90.3% of the single implant placements in this study, the operator's level of experience may have influenced the number of surgical complications.
This study estimated that 33.2% of implants were expected to have at least one biological complication after 5 years. The most frequently observed biological complication after implant placement was soft tissue-related, with an estimated rate of 13.7% after 5 years. This
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is in keeping with Jung et al18 (9.7% after 5 years). Soft tissue complications such as periimplant mucositis, gingival overgrowth and recession, arise from the inflammatory host response to the biofilm formation at the trans-mucosal zone around implants.12 Ensuring the restoration allows for optimal oral hygiene can reduce soft tissue complications.
Integration and bone loss complications were almost as frequently observed as soft tissue complications, with an estimated rate of 12.1% after 5 years. Osseointegration and bone loss issues may have been influenced by local site factors such as poor bone quality and/or inadequate quantity, hard tissue-related surgical complications encountered during time of implant placement (bony dehiscences and/or fenestrations) or possible inadequate surgical technique by the inexperienced operators. Surgical experience and the effect of the learning curve has been reported to influence the osseointegration of dental implants, with a higher osseointegration rate reported in implants placed by experienced clinicians compared to inexperienced operators (94.4% vs. 84.0%).32 Lambert et al33 reported that implants placed by inexperienced operators for example students (that performed less than 50 implant procedures) were more than twice as likely to fail compared to those implants placed by experienced clinicians (that placed more than 50 implants).
This study showed a cumulative pre-definitive restorative complication incidence of 7.1%, with the most common restorative complication observed during the pre-definitive restoration phase being healing abutment loss or loosening (23 events from 451 implants).
The
cumulative definitive restorative complication incidence was 14.2%, within which screw and abutment loosening, which comprised 27.0% of all definitive restorative complications, had a cumulative incidence of 3.8%. Abutment screw loosening in ISSCs has been widely reported in clinical studies and systematic reviews.3,6,7 Jung et al reported a screw and abutment
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loosening incidence of 8.8%3 and 5.8%, respectively.18 The 3.8% screw and abutment loosening incidence rate reported in this study did not include 27 cases of crown loosening which had no cause description. It is probable that a screw, abutment or cross-pin related issue could have caused crown loosening. Restorative screws used to retain an implant crown can loosen for many reasons including (i) screw joint relaxation, (ii) inadequate passive fit, (iii) poor component fit, and (iv) excessive loading of the screw joint.17 After including the 27 cases of loose crowns into the number of abutment and screw complication events, the cumulative incidence of abutment and screw loosening was 9.9%, which is closer to the incidence rate reported by Jung et al.3 Patients who did not return for follow-ups may have influenced the low rate reported here, as many may have returned to their referring dentists for further dental care, or a change in their public health eligibility status may have resulted in their seeking private dental care.
The majority (93.5%) of the ISSCs in this cohort were screw-retained, which was consistent with the philosophy of restoration retrievability amongst prosthodontists across Australia.19 While some studies20,21 found no significant difference between cement- and screw-retained restorations with regards to implant survival or crown loss; advocates of screw retention22, 23 emphasize retrievability for ease of managing technical complications such as porcelain fracture, occlusion adjustment, contact point correction and aesthetic discrepancies.
Multiple studies3, 18, 24, 25 have identified a wide range of complications with implant therapy. Comparison of studies can be difficult as diagnostic parameters are not standardized and the definitions of success, survival and complications often vary. Statistical analysis used for complication reporting amongst researchers was also inconsistent, including the use of terms such as “annual rate”, “cumulative incidence”, “cumulative complication rate”, “estimated
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complication-free rate” and “complication rate per 100 implant-years estimate”.
In a
systematic review by Berglundh et al25, biological and technical complications were considered in only 40 to 60% and 60 to 80% of the studies, respectively. Goodacre et al7 concluded that “it was not possible to calculate an overall complications incidence for implant prostheses because there were no multiple clinical studies that evaluated all or most of the categories of complications”. Such observations suggest that the incidence of implantrelated complications may be under-estimated and should be interpreted with caution.
There are inconsistencies in the reporting of implant-related complications among researchers. Goodacre et al26 defined an implant complication as “a secondary condition that developed during or after implant surgery or prosthesis placement”. They also stated that the occurrence of a complication did not necessarily indicate that sub-standard dental care was provided nor did it necessarily mean clinical failure. Understanding that complications in implant dentistry do occur is important for both the clinician and patient, and is a key rationale for maintenance, which has been suggested to be every three or four months in the first year, then yearly afterwards.27,
28, 29
Clinicians may consider informing patients of
potential complications during the treatment planning stage to manage patient expectations and minimise patient dissatisfaction with future adverse outcomes.
Certain biases and limitations exist in this study which may have influenced the results. The mean follow-up time was short, being 2.18 years for single implants and 2.03 years for ISSCs, whereas a mean follow-up time of at least five years is common in most systematic reviews.3, 18 The number and type of complications may be under-reported due to loss of follow-up of patients who returned to their referring dentists for further care. The MDS’s teaching philosophy encourages a one-stage surgical placement of implants, no immediate
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loading of implants and screw-retained restorations for retrievability. These philosophies have predetermined data collection regarding two-stage placement of implants, immediate loading of implants and cemented ISSC designs.
All analyses assumed that implant
complications and/or failures occurred independently. Other studies30,
31
have identified
possible clustering effects (i.e. more than one implant failure per patient, not necessarily in the same area or quadrant) for implants and ISSCs.
These clustering effects were not
included in the analysis to facilitate a direct comparison of results with other studies that did not perform cluster modelling.
During data collection, treatment details were not always clearly recorded in patient records. Information such as methods of osseointegration assessment, baseline and progressive radiographic assessment, periodontal probing depths around implants at periodic review visits, restorative details (abutment types and materials), implant identification and management of complications were sometimes unclear. Incomplete or unclear records in retrospective studies may have resulted in an under-representation of complication occurrences.
Accurate and detailed records can improve quality patient care and inter-
clinician consistency in all clinical areas, and in teaching environments such as MDS where dental care is provided by multiple clinicians.
Conclusion Single tooth replacement with implant therapy within a teaching environment has high survival rates for both the implant and the single crown. However, complications do arise and this fact should be communicated clearly to the patient from the outset.
The
understanding that implant therapy is not complication-free emphasises the importance of ongoing maintenance. This paper only described the occurrences of complications; further
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analysis with a focus on the association between patient, surgical and restorative variables and complications would facilitate better understanding of the causes and therefore possible preventive measures.
Acknowledgements: This study was approved by the Dental Health Services Victoria Human Research Ethics Committee (Approval No. 217) and is funded by the Melbourne Dental School Research Committee.
The authors would like to thank Dr. Angelos Sourial, Dr. Peter Apostolopoulos and Dr. Vivien Yeo for assisting with data collection, Ms. Ann Thomson for carrying out data-entry and Ms. Sandy Clarke for carrying out statistical analysis. The authors have no conflicts of interest to report in connection with this study.
References 1. Chang M, Wennstrom J, Odman P, Andersson B. Implant supported single-tooth replacements compared to contralateral natural teeth - Crown and soft tissue dimensions. Clinical Oral Implants Research 1999; 10(3): 185-194. 2. Torabinejad M, Anderson P, Bader J, Brown L, Chen L, White S, et al. Outcomes of root canal treatment and restoration, implant-supported single crowns, fixed partial dentures, and extraction without replacement: a systematic review. Journal Of Prosthetic Dentistry 2007, Oct; 98(4): 285-311. 3. Jung R, Pjetursson B, Glauser R, Zembic A, Zwahlen M, Lang N. A systematic
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Figure legends Fig 1. Distribution of single implant placements and ISSC restorations by clinician type. Fig 2. Distribution of patients according to age group. Fig 3. Implant connection type. Fig 4. Method of ISSC retention. Fig 5. Distribution of types of surgical complications.
Table legends Table 1. Overview of patient profile Table 2: Cross-tabulation of surgical and restorative status Table 3. Implant failure rates Table 4. Types of hard tissue surgical complications Table 5. Biological complications Table 6: Restorative complications
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Abbreviations and acronyms: DTF= Direct to fixture HIPS = haemorrhage, infection, pain and/or swelling ISSCs = Implant-supported single crowns MDS = Melbourne Dental School RDHM = Royal Dental Hospital of Melbourne SPSS = Statistical Package for the Social Sciences
Table 1. Overview of patient profile Categories
Descriptions
N (%)
Gender
Male
121 (29.8)
Female
285 (70.2)
Diabetes
Yes
24 (5.9)
Osteoporosis/Osteopenia
Yes
6 (1.5)
Tooth wear
Yes
134 (33.0)
Smoking status
Smoker
69 (17.0)
Previous Smoker
50 (12.3)
Non-smoker
281 (69.2)
Not Recorded
6 (1.5)
Table 2: Cross-tabulation of surgical and restorative status Definitive Restorative Analysis
Total
Included
Excluded
Included
432
188
620
Excluded
12
0
12
444
188
632
Surgical analysis
Total
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Table 3. Cross-tabulation of method of restoration retention, implant region and implant platform. Implant Region Implant Method of Retention Platform Anterior Posterior Direct-to-fixture (n=107) (24.1%) 50 (46.7%) 57 (53.3%) Cross-pin (n= 120) (27.0%) 50 (66.7%) 40 (33.3%) Cement (n=5) (1.1%) 5 (100%) 0 Bone Level Not Recorded (n=5) (1.8%) 5 (62.5%) 3 (37.5%) Total (n=240) (54.1%) 140 (58.3%) 100 (41.7%) Direct-to-fixture (n=155) (34.9%) Cross-pin (n=33) (7.4%) Tissue Level Cement (n=9) (2.0%) Not Recorded (n=7) (1.6%) Total (n=204) (45.9%)
Total
Direct-to-fixture (n=262) (59.0%) Cross-pin (n=153) (34.5%) Cement (n=14) (3.2%) Not Recorded (n=15) (3.4%) Total (n=444)
8 (5.2%) 7 (21.2%) 0 0 15 (7.4%)
147 (94.8%) 26 (78.8%) 9 (100%) 7 (100%) 189 (92.6%)
58 (22.1%) 87 (56.9%) 5 (35.7%) 5 (33.3%) 155 (34.9%)
204 (77.9%) 66 (43.1%) 9 (64.3%) 10 (66.7%) 289 (65.1%)
Table 4. Implant failure rate
Total failures/ Total implant surgeries
Cumulative incidence %
Rate per 100 implant years estimate (CI 95%)
17/622
2.7
1.26 (0.73 – 2.01)
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Table 5. Types of hard tissue surgical complications Hard tissue complication type
N
Primary stability not obtained
20
Fenestration/dehiscence
14
Unexpected sinus involvement
11
Insufficient bone
10
Angulation error
5
Trauma to adjacent tooth
3
Total
63
Table 6. Biological complications
Biological
Total events/
Cumulative
Event rate per 100 implant years
complication
total implants
incidence %
estimate (CI 95%)
Soft tissue
40/620
6.5
2.96 (2.11-4.03)
Integration/bone
35/620
5.6
2.59 (1.80-3.60)
HIPS
25/620
4.0
1.85 (1.20-2.73)
Post-op HIPS
8/620
1.3
0.59 (0.26-1.17)
Post-op external
1/620
0.2
0.07 (0-0.41)
109/620
17.6
8.06 (6.62-9.72)
loss
trauma Total
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Table 7. Restorative complications Total events/
Event rate per 100 Cumulative
Restorative complications
total
implant years estimate incidence %
implants Pre-definitive
restorative
(CI 95%)
32/451
7.1
3.53 (2.41-4.98)
Retention
22/444
5.0
2.44 (1.53-3.70)
Screw/abutment
17/444
3.8
1.89 (1.10-3.02)
Occlusion
11/444
2.5
1.22 (0.61-2.19)
Aesthetics
8/444
1.8
0.89 (0.38-1.75)
Veneer
5/444
1.1
0.56 (0.18-1.30)
Total*
63/444
14.2
7 (5.38-8.95)
complication
* Excluding pre-definitive restorative complications.
Fig 1. Distribution of single implant placements and ISSC restorations by clinician type.
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300
261
250
Number of implants
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Fig 2. Distribution of patients according to age group.
184
200 150
146 Tissue Level
100 50
Bone Level 15
14
0 Internal External Not Recorded Connection Connection Implant connection type
Fig 3. Implant connection type.
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Fig 4. Method of ISSC retention.
Fig 5. Distribution of types of surgical complications.
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