Implants for life? A critical review of implant-supported restorations

Transcription

1 journal of dentistry 35 (2007) available at journal homepage: Review Implants for life? A critical review of implant-supported restorations David Bartlett * Floor 25, Prosthodontics, King s College London Dental Institute, Guy s Tower, London Bridge SE1 9RT, United Kingdom article info Article history: Received 4 June 2007 Received in revised form 7 June 2007 Accepted 3 July 2007 Keywords: Implants Prosthodontics Critical review Crowns Longevity abstract Aim: This review critically appraises the literature on implant-supported restorations. Method: The review was conducted in March 2007 using OVID Medline with the search terms, limited to the English Language, of implant, crown, bridge, fixed and removable partial dentures and complete dentures. From a total of 5135 papers combining implants and implant-supported restorations only 131 were found, after a thorough hand search, to be relevant to the restoration of implants. Results: The outcome of implant fixtures have consistently been shown to be successful over the long-term. However, the same focus of research into the restorations used to support implants has not. Where research is available to guide clinicians towards a particular technique the rigour of the research is limited. Conclusion: More emphasis by the research community on the outcome of restorations supported by implants is needed. # 2007 Elsevier Ltd. All rights reserved. 1. Introduction The success of implants is widely proclaimed in the literature and by dentists when discussing outcome with their patients. Patients and dentists perceptions of implants are trouble free tooth replacements but does the literature support this? Whilst implant fixtures have a good record of success and longevity, the restorations used to replace teeth can develop problems which are often overlooked and underestimated. This clinically based article reviews the literature on implantsupported restorations and appraises current techniques. It is not aimed to be a comprehensive and will briefly review and critically appraise the longevity of other fixed restorations used to replace teeth. Considering the time implants have been available as an option for tooth replacements there have been surprisingly little research on the restoration of the implant fixture. In an OVID database search conducted in March 2007 using the search phrases listed in Table 1 a total of 131 references specifically related to prosthodontic applications for implants were found. By comparison that for composites and materials testing revealed Implant fixtures Ever since Brånemark et al. proposed that implants could reliably integrate with bone both manufacturer s and dentists have attempted to push the frontiers of development. 2 5 But a closer look at Brånemark s work shows the meticulous scientific methodology which has rarely been repeated in dental clinical research. Few researchers have the patience The main findings in the manuscript were presented at the annual meeting of the British Society for Restorative Dentistry in Brighton * Tel.: address: [email protected] /$ see front matter # 2007 Elsevier Ltd. All rights reserved. doi: /j.jdent

2 journal of dentistry 35 (2007) Table 1 Phrases used in OVID search on 10th March 2007 Phrase Result 1 Dental implant (s) 73,213 2 Fixed partial denture, removable 18,828 partial denture, crown, bridge 3 Combine 1 and 2 5,135 4 Limit to English language 1,341 5 Result after hand search Composite (s) 16,318 7 Materials testing 22,018 8 Combine 6 and 7 3,771 and confidence to publish a new clinical technique with longevity data approaching 10 years. What was so unique about Brånemark s work was that it was a fait de complies. In 1983, Brånemark et al. tested the hypothesis did a biological seal develop around an implant and allow osseo-integration to occur? 3 The results from 3250 fixtures inserted into 400 subjects over a maximum follow-up time of 16 years showed a biological seal had indeed been formed. The impact of this research started others to investigate this concept and Zarb et al. introduced the concept of osseo-integration at the Toronto conference in the 1980s. The explosion of interest in North America as a result of this ground breaking research changed dentistry and led to further developments in implants which never quite matched the intensity of research started by Brånemark. The data from more recent longevity studies wholeheartedly support Brånemark s initial hypothesis with Karoussis et al., 6 Naert et al. 7 and Bahat 8 reporting the success of implants at around 95%. Esposito and others in a Cochrane database review concluded On a patient base there were no statistical differences for failure or bone levels between different implant systems. Therefore, on the basis of current research it is safe to say that implants fixtures have a good prognosis. But what is less understood is how the restorations supported by the fixtures perform. investigated by Pjetursson et al. 13 and although the findings compared reasonably well to more conventional fixed fixed designs they had a higher failure rate (median survival of 81.8% CI %). The evidence for the longevity of minimal preparation bridges appears to be even less with reports ranging between 5 and 7 years. 15,16 Interestingly, Pjetursson et al. also systematically reviewed the outcome of implant-supported bridges. 17,18 The reported success rates of 95% (CI %) after 5 years and 86.7% after 10 years ( %) showed success similar rates to conventional bridges. 18,1 In their paper the authors reported that the most common reason for failure of the implantsupported restoration was fracture of the abutment veneer (14%) and screw loosening or fracture (7.3%). 18 They concluded that biological and technical complications with implantsupported restorations were frequent. In a different study Becker 19 observed better outcomes in a 10 years study on 60 cantilever retained bridges supported by ITI fixtures. All 60- tooth replacements after 10 years showed no complications and the restorations remained in satisfactory function. However, this degree of success is not normally identified with most workers reporting some complications with the restorations. 20 The critical reviews by Pjetursson et al. 14,18 and Tan et al. 9 on implant, conventional and cantilever bridges reported the percentage of restorations which were problem free. At 10 years conventional bridges were reported to be the most problem free restoration (71% CI %) whilst implantsupported bridges and cantilever conventional bridges were 61.3% (CI %) and 63% (CI %), respectively. Although, systematic reviews tend to restrict the total number of publications the trend suggests that conventional bridges seem to produce less complications than implant-supported bridges which seems to correspond to clinical experience. 4. Comparison of implant-supported to conventional restorations 3. Longevity of implant-supported and other restorations The options for tooth replacement have traditionally been tooth-supported restorations. Since the introduction of implants the role of the conventional bridge has been somewhat questioned. However, recently a series of papers systematically reviewed the longevity and success of fixed fixed and simple cantilever designed conventional bridges. Tan et al. 9 reported that the median survival of conventional bridges after 10 years was 89.1% (95% confidence interval between 81% and 93.8%). The most common reason for failure was loss of retention (6.4%), material failure (3.2%), caries (2.6%) and periodontitis (0.7%). Other researchers have shown longevity of conventional bridges to vary from <15% failure at 10 years and 30% at 15 years 10 to 87% survival at 12 years in a Dutch study on 1674 bridges. 11 These and other studies suggest that the longer the bridges are in service, the more likely failure eventually occurs and the crucial time for change is around 10 years. 12,13 The success of cantilever bridges was An interesting study by Walton and MacEntee. 21 reported the outcome of a questionnaire based study which investigated the perceived barriers to implants. Surprisingly, 36% out of a sample of 101 elderly Canadians refused free implants. The most commonly quoted reason for refusal was fear of surgery. The most common reasons quoted by those choosing free implants were those concerned with poor chewing function, poor speech and dissatisfaction with their appearance. This relatively small study highlights that implants are not always the treatment of choice. Raghoebar et al. 22 in a prospective randomised controlled trial (RCT) compared the outcome of conventionally made dentures and implant-supported dentures. The outcome at 1, 5 and 10 years unsurprisingly reported that the implant supported dentures at all time periods produced fewer complaints than the conventional dentures. Bragger et al. investigated the outcome of 41 conventional three units bridges and 52 patients with 59 single tooth implants in another RCT. 23 The authors observed that the initial costs were higher for conventional bridges and although the implants needed more clinical visits the total time taken to

3 770 journal of dentistry 35 (2007) make both restorations was similar. Attard et al. 24 in another study compared the outcome of conventionally implantsupported overdentures to implant-supported prostheses in 90 patients. Over the short- and long-term the removable implant-supported overdentures were cheaper and produced fewer complications than the fixed prosthesis and consequently this group of researchers recommended overdentures as the treatment of choice for the edentulous mouth. The success of single tooth implants shows a similar success rate to that of implant-supported bridges. 25 But even if the fixtures present few complications the restorations have complications. Krennmair et al. reported that 9 (9.9%) from 93 cemented crowns loosened in a 3 years study 26 and Vermylen et al. 27 reported eight crowns (32%) needing major or minor replacement again in a 3 years study. In a study reported by Davis et al. 28 investigating the outcome and maintenance of implants-supported dentures from 37 patients over a 5 years period the authors observed that when implant-supported dentures opposed each other the acrylic needed replacing more frequently (44 times) than when they opposed teeth (twice). They concluded that maintenance of implant versus implant-supported dentures required much higher maintenance. In summary both fixed and removable prosthodontic rehabilitations have maintenance costs and are associated with failure. Problems arise in fixed restorations more frequently with being the most common veneer fracture and with acrylic dentures with tooth fracture and wear of acrylic. 5. Influence of design on outcome of restoration 5.1. Overdentures There is comparatively little published research to guide practitioners on how the design of abutments influences outcome of the restoration. In a study by Nedir et al patients were treated with 538 implants over an 8 years study. Subjects received 55 implant-supported overdentures and 265 implant-supported bridges with an overall success of 99.2% for the fixtures, however, 66% of the removable and 13% of the fixed prostheses development complications. The authors reported no differences between the outcomes for cemented versus screw-retained bridges but there were more complications with ball attachments than bar attachments for the overdentures. Godfredsen et al. 30 reported the results of an RCT comparing implant supported overdentures and the authors reported twice as many complications developed with the bar attachment than the ball and socket. To complicate matters more MacEntee et al. 31 in another RCT investigated outcome with a bar or ball attachment and reported that most complications developed in the first year with 90% of repairs occurring with the ball and socket (mean number of repairs 6.7 per person with a ball and 0.8 with a clip and bar). Other nonrct investigations comparing the bar and ball attachment have tended to suggest that the bar systems had more complications. 30,32,33 Magnets have recently received more attention following improvements in design. Davis and Packer 32 in a comparative study observed that patients in their study found magnets less comfortable and had more susceptible plaque deposits than ball or bars but overall their subjects were satisfied with all systems. Naert et al. in a 5 years prospective study also observed more plaque on overdentures retained by magnets compared to ball or bar attachments. 34 In summary and based on the findings from most studies a ball and socket system seems to produce less problems than a bar or magnets but there is no consensus Single teeth Retention of an abutment to the fixture can be screw or cement retained. Zarb and Schmitt 35 in an early study appraised the benefit of a screw retained restoration by concluding that it allowed easier retrievability and was useful in situations where inter arch space was limited but they tended to be bulkier than cement retained crowns. The authors recognised that most dentists preferred a cement-retained restoration but the choice often depended on the emergence profile of the implant and the need for augmentation. Preiskel and Tsolka 36 in a follow-up study compared 124 screw retained to 161 cement-retained restorations and observed that eight abutment screws needed tightening, one gold screw needed replacing whereas no decementation occurred. Vigolo at al. 37 reported no problems with either screw or cemented restorations in an RCT on 12 patients over a 4 years period. Weber 38 investigated 152 ITI implants over a 3 years period and observed no preference from patients for a screw or cemented restoration. In summary, it appears that cementretained restorations seem to be preferred by most dentists but patients may not necessarily notice the difference. If cement retained restoration is chosen what cement should be used? Temporary cements seem to offer dentists the possibility of retrievability but they need to be used carefully. Although temporary cements tend to be softer and less adhesive than permanent cements they can be quite retentive particularly if used for cementation of crowns where the abutments are long and parallel sided. A number of authors have recognised that resin composites, zinc phosphate and glass inonomers have enhanced retention compared to temporary cements but their use will vary between clinical situations. What patients feel about the concept of retrievability of an expensive restoration is unknown and would make an interesting study. 6. Conclusion The introduction of implants revolutionised prosthodontics. The expansion of the commercial world and the business of dentistry have to some extent drawn away from the meticulous research principles developed by Brånemark. However, whilst research continues to be proactive for fixtures the same cannot be said for their prosthodontic rehabilitation. There is comparatively little research to guide practitioners on how to restore implants. Considering the vast numbers of implant systems and variations in products within companies this may not be entirely surprising. However, in such an important area of dentistry there is a need for more research on how to guide us on the most reliable restorations.

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