J Dent Educ. 69(4): 414-418 2005
© 2005 American Dental Education Association
From the Students' Corner |
Single-Unit Implants Versus Conventional Treatments for Compromised Teeth: A Brief Review of the Evidence
Clarence S. Tang, B.A.;
Adam E. Naylor, B.S.
Mr. Tang and Mr. Naylor are both Predoctoral Students, Class of 2006, University of North Carolina School of Dentistry. Direct correspondence and requests for reprints to Mr. Clarence Tang, University of North Carolina School of Dentistry, Student Mailboxes 006-065, CB #7450, Chapel Hill, NC 27599-7450; 919-321-0239 phone; 919-966-5795 fax; tangcs{at}email.unc.edu.
Key words: dental implants, implant-supported dental prosthesis, single-tooth implants, endodontics, periodontics
Submitted for publication 12/09/04;
accepted 01/28/05
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Abstract
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The goal of preserving the natural dentition has long provided the foundation for clinical decision making in dentistry. Current trends in implant dentistry have weakened this paradigm as many practitioners have moved quickly to adopt implant dentistry as a new standard of care; however, the rapidity of this shift is a cause for concern among others. Many short-term studies have reported favorable data supporting the growth of single-unit implant dentistry, but the lack of standardized outcome evaluations and broadly conceived dimensions of performance makes it difficult to compare these reports. Thus, even with the exciting new treatment options implant dentistry offers patients and practitioners, all due consideration should first be given to treatments aimed at preserving and restoring compromised teeth before pursuing extraction and replacement. This article examines this premise from five perspectives: form, function, survival, management of complications, and quality of life.
The goal of preserving the natural dentition has long provided the foundation for clinical decision making in dentistry. To practitioners and patients alike, tooth extraction has generally been considered a treatment of last resort. Current trends in implant dentistry have weakened this paradigm as practitioners’ attention has been drawn towards providing tooth substitutes often touted as equal or even superior to the preservation of natural teeth. Many practitioners have moved quickly to adopt implant dentistry as the new standard of care, but the rapidity of this shift is a cause for concern among others.
While it is true that implant dentistry holds a great deal of promise, a cautious approach to embracing this technology is well advised, as our understanding of the long-term implications of many forms of implant treatment, including single-tooth replacements, is still in its infancy.1 Even with the exciting new treatment options implant dentistry offers patients and practitioners, all due consideration should first be given to treatments aimed at preserving and restoring compromised teeth before pursuing extraction and replacement. This article examines this premise from five perspectives: form, function, survival, management of complications, and quality of life.
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Form
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One of the appeals of implant dentistry is the promise that the esthetic form and daily function of a single-unit implant is as close an approximation to that of a natural tooth as is possible to achieve. Esthetics, in particular, is of paramount importance to many patients. Significantly, esthetic failures in implant dentistry are far more common than mechanical failures, especially in the anterior dentition.2 A failure on the part of the practitioner to recognize esthetic risk factors like high patient expectations, a high smile line, poor gingival quality, poor papillary morphology, and low bone height3 will most often lead to patient dissatisfaction with implant dentistry. Predictable results are impossible to achieve without properly managing these factors.
Soft tissue management is a key aspect of esthetic management in implant dentistry. The placement of a foreign body in bone has implications for marginal bone height, which in turn has a direct effect on soft tissue contours.4,5 Achieving esthetic soft tissue contours around the final restoration, therefore, begins with meticulously planning the relationship between the final restoration and surrounding bone height. This planning step must include an assessment of the mesiodistal, buccolingual, and interocclusal space available for implant, restoration, and biologic width. Additionally, the practitioner must determine if the existing bony morphology is adequate for ideal angulation and vertical depth of implant placement. If deemed inadequate, site development—including ridge augmentation, sinus lifts, orthodontic movement of adjacent teeth, and soft tissue augmentation—should be considered.6
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Function
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Functionally, a well-osseointegrated implant differs from a tooth most significantly by its lack of a periodontal ligament (PDL). Two of the resulting deficiencies are an absence of the PDL’s cushioning effect and proprioceptive ability. Although these deficiencies do not necessarily affect a patient’s overall ability to chew,7 they have important implications for implant survival. To address the loss of a natural cushion and the ability to sense overloading, most treatment protocols recommend restoring posterior single-unit implants slightly out of occlusion in order to compensate for the axial compression of the PDL in the adjacent natural teeth upon loading.8 Failure to do so may cause occlusal overload, which is generally accepted as a major cause for loss of implant osseointegration.9 Unfortunately, there are no clear solutions for controlling lateral forces, which are not only harder to identify and control, but also are more detrimental than axial forces.10
A third deficiency caused by the absence of a PDL around an implant is its lack of regenerative potential,11 which limits the ability for repair disruptions of any of osseointegration. There is evidence that it is possible to achieve steady-state alveolar bone levels around an implant;12 however, unlike the PDL, implants do not play an active role in the dynamic maintenance of that bone. Thus, incremental losses in osseointegration throughout the time an implant is in service are cumulative and irreversible. Unfortunately, peri-implant tissues are subject to mechanisms of infection similar to periodontal disease,13 and implant sites have been shown to be more difficult to keep clean and healthy than natural tooth sites.14 These findings suggest that implants are perhaps at greater risk for eventual loss than natural teeth, especially in patients already prone to periodontal disease.
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Survival
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Dental implants have by no means constituted the only significant recent advance in dentistry. In endodontics, for instance, the use of microscopes, titanium files, computerized apex locators, and ultrasonic instruments are but a few of the developments that have enabled practitioners to perform endodontic treatment with greater precision and efficiency, fewer errors, and better success rates than ever before.15 Of course, success in endodontic treatment is not solely dependent on instruments and technique. It is also affected by such factors as level of disease progression (i.e., presence of periapical pathosis), case selection, iatrogenic errors, and, most importantly, post-endodontic treatment control of coronal microleakage.16,17
The three-year success rate of endodontic treatment in resolving pulpal or periapical disease has been reported to be as high as 98 percent,18 varying significantly with the level of training the practitioner has in performing endodontic therapy (i.e., generalist vs. specialist).19 Long-term survival of these teeth is somewhat lower: one retrospective study of 1007 teeth reported a ten-year survival rate of just under 90 percent.20 Further investigations have demonstrated that prosthetic factors such as remaining tooth structure and management of occlusal forces21 are the most important contributors to the long-term survival of an endodontically treated tooth.
Unfortunately, very little long-term data exists for evaluating implant success rates.22 Nonetheless, preliminary indications seem to suggest that single-unit implant-retained restorations have the potential to enjoy long-term success comparable to those of endodontically restored teeth. Multiple studies have reported five-year implant survival rates upwards of 95 percent,23–25 and Kaplan-Meier estimates of ten-year survival approximate 90 percent.26 Risk factors such as poor patient oral hygiene, poor alveolar bone quality, and smoking have been shown to have a negative impact on implant survival rates, but the true extent of that impact has yet to be determined.27
Advances in periodontal regenerative therapy for reversing the process of supporting alveolar bone loss have also occurred in the last decade.28 However, many of these regenerative techniques are, at present, only applicable for treating limited clinical presentations (localized rather than generalized bone defects, for instance), and the predictability of these techniques seems inversely related to the severity of the disease experienced.29 Simpler, less technique-sensitive regenerative procedures need to be developed that can be more universally and predictably applied.30 Nonetheless, used in conjunction with other conventional periodontal therapies such as pocket reduction surgery,31 root resection,32 and hemisection,33 regenerative periodontal techniques offer patients greater potential for successfully maintaining compromised teeth than ever before.
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Management of Complications
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There is some suggestion that there are "a greater number of clinical complications associated with implant prostheses than any other types of prostheses," including conventional FPDs and single crowns, resin-bonded prostheses, posts and cores, and all-ceramic crowns.34 Such mechanical complications—involving failure of the prosthesis (e.g., porcelain fracture) or failure of an implant component (e.g., the abutment screw)—have been reported to occur as much as 17 percent of the time in the first five years of service.35 Replacement of the prosthesis, implant component, or implant fixture may be indicated to manage these complications, depending on what failed and what can be salvaged.
As site preparation and implant placement are surgical in nature, they carry risks common to most surgical procedures, including hemorrhage, neuro-sensory disturbances, and adjacent tooth devitalization.36 Surgical complications are most appropriately referred to specialists trained in the management of such incidents.
Implant complications involving failure of osseointegration are commonly divided into two categories: early and late. Early failures—indicative of an implant that never successfully osseointegrated in the initial months after placement—have been linked to impaired healing ability of the host bone site, disruption of a weak bone-to-implant interface after abutment connection, and infection in situations with complicated surgery.37 An early implant failure must be removed and the site left to heal before considering retreatment either with another attempt at a single-unit implant or with conventional crown and bridge dentistry.
Late implant failures indicate that successful osseointegration was initially achieved, but was then progressively lost over time. Late failures are generally thought to be caused by occlusal overload and/or bacterial growth leading to peri-implantitis.38 Signs of failing implants include increasing radiographic bone loss, soft tissue pocketing, bleeding or suppuration on probing, and pain on percussion or torquing. After addressing any problems of occlusion, the management of such failing implants includes various combinations of mechanical therapy, antimicrobial therapy, antibiotic therapy, and, in the most advanced cases, resective or regenerative periodontal surgery.39 However, no controlled studies have been conducted to assess the effectiveness of these supportive measures.40
Of course, there are also risks associated with conventional treatments aimed at preserving compromised natural teeth. Regenerative periodontal therapy, for instance, presents the potential for surgical complications similar to those inherent to implant therapy. Endodontic treatment incurs mainly the risk of complications caused by iatrogenic errors such as missed canals, root perforations, instrument separation, ledging of canal walls, and inadequate root fill. Many of these complications do not necessarily lead to failure, but if so, they often can be successfully managed with either surgical or non-surgical retreatment.41 There are no specific guidelines for management of failed root canal treatments, but attempts at nonsurgical retreatment are generally preferred before moving on to more invasive surgical methods,42 partly to avoid the potential for surgical complications. Tooth survival has been shown to decline dramatically with each additional treatment performed,43 probably due to successively more tooth structure being removed at each retreatment, thereby increasing the potential for vertical root fracture44 and subsequent extraction.
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Quality of Life
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A recent market report acknowledged that "implant services involve higher fees than traditional services" and concluded that it was "important to emphasize to patients that the quality of life far outweighs the differential in fees."45 That implants provide better quality of life outcomes than conventional treatments seems to be a commonly held perception among those endorsing the rapid adoption of implant dentistry; however, there is very little supporting evidence for this statement.46 Among the few studies undertaken, implant dentistry has been more clearly shown to increase quality of life measures for patients when used as anchorage for removable prostheses47 than when used to restore a bounded edentulous space, such as a single-tooth replacement.48
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Conclusion
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Although implant-supported restorations have been effectively used for managing existing edentulous spaces, much of the evidence supporting the use of single-unit implants for replacing natural teeth is based on short-term data collected under optimal conditions that may not be replicable in most private practices. More importantly, the lack of standardized outcome evaluations makes it difficult to compare these reports.49 Furthermore, no studies have yet been designed to measure and report broadly conceived dimensions of performance such as form, function, survival, management of complications, and quality of life.
There is no doubt implant dentistry has great potential, and it is certain that the broad interest of numerous advocates will ensure the continuous advancement of ways in which implants can be used in dentistry. However, until there are sufficiently convincing data available to make truly informed choices about implant use, practitioners should be cautious of the wholesale adoption of this technology.
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Acknowledgments
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This manuscript was originally written to fulfill requirements for the UNC Predoctoral Dental Implant program directed by Matthew L. Hopfensperger, D.D.S., M.S. The authors also wish to thank Dr. Jim Bader, UNC-Chapel Hill School of Dentistry, for his insights and his assistance in reviewing drafts of this manuscript.
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Bootstrapping Student Publication in the JDE: An ADEA Council of Students Initiative
J Dent Educ.,
October 1, 2007;
71(10):
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