Elliot Abt DDS, MSc, MS
There is evidence to suggest that implant-supported cantilever bridges are a valid treatment modality.
While implant-supported cantilever bridges may be a viable treatment, the strength of evidence reported in this review is inconclusive.
In patients requiring replacement of missing teeth, what are the survival and complication rates of implant-supported cantilever bridges?
Two investigators independently searched one database and handsearched several journals for English-language studies, up to December, 2007. 412 abstracts yielded 5 studies meeting the inclusion criteria. Included studies were limited to cohort designs examining the survival and complication rates of implant-supported cantilever bridges. Bridge survival rate was the primary outcome of the review which was reported as percent survival with 95% confidence intervals.
5 and 10-year survival rates for implant-supported cantilever bridges were 94.3% (95%CI 84.1-98%) and 88.9% (95%CI 70.8-96.1%), respectively. This is based on five included studies, encompassing 354 implants and 155 prostheses. Several estimates were also given for technical and biological complications. Confidence intervals around many estimates were quite wide, reflecting the imprecise nature of the data.
There is evidence to suggest that implant-supported cantilever bridges are an acceptable treatment based on 5 and 10-year survival rates approximating 94 and 89 percent, respectively. 5-year rates for technical and biological complications did not exceed 10%.
Source of Funding:
This systematic review was supported by the Clinical Research Foundation (CRF) for the Promotion of Oral Health, Brienz, Switzerland.
Importance and Context:
Dental implant therapy has provided patients with fixed reconstructions which, in many cases, would not have been possible with conventional fixed prostheses. Oftentimes, anatomic and/or financial constraints preclude the placement of enough implants to avoid implant-supported bridges. Thus, implant-supported bridges present an attractive alternative to multiple single-tooth implants, or implant/tooth-supported bridges. Little evidence exists on the success of implant-supported cantilevered bridges, and cantilevers of any type have often been discouraged in undergraduate dental curricula. If cantilevered implant bridges offer success rates comparable to other methods of tooth replacement, practitioners could use this evidence to facilitate clinical decision making.
Strengths and Weaknesses of the Systematic Review:
This review began with a research question examining the survival rates of implant-supported cantilever bridges. This is a broad question, which is common in traditional or narrative reviews. Systematic reviews begin with a narrow, focused question and an exhaustive search for evidence relevant to this question. A systematic review on this topic would typically have compared the survival of cantilevered implant-bridges to other methods of tooth replacement. This was done only for a secondary outcome (alveolar bone loss). The authors used only one database for searching, did not consider non-English publications, did not search for non-published literature, and experts were not contacted for studies meeting the inclusion criteria. There was no assessment of the quality of the included studies. Additionally, due to bias and confounding, a pooling of data (meta-analysis) should not be a prominent component of reviews of observational studies as they are likely to provide precise, but spurious results. 1 With many deviations from systematic review protocol, this article appeared to be more of a narrative review, at significant risk of bias.
Strengths and Weaknesses of the Evidence:
The evidence presented in this review had a number of shortcomings. Of the five included studies, only two were reported to have implant cantilever bridges as their primary focus. Additionally, these two studies had changes in alveolar bone height as their primary outcome, a surrogate outcome indirectly related to true outcomes such as prosthesis survival. All included studies were cohort designs, a type of observational study at risk of confounders, and the quality of the studies meeting the inclusion criteria was not addressed. As this review addressed a therapeutic intervention, the existence of randomized trials could have been addressed. There appeared to be significant heterogeneity among the included studies: assessing mesial and distal cantilevers, maxillary and mandibular prostheses, and different types and numbers of implants supporting the cantilevers. Providing one summary estimate for a small sample of many types of implant cantilever bridges produces a distorted picture of prosthesis survival.
Implications for Dental Practice:
This review showed evidence that implant-supported cantilever bridges are a viable treatment. It appears premature to support the appropriateness of this evidence due to the small number of included studies, at risk of bias, and with significant heterogeneity among studies. Large, high quality trials or prospective cohort studies are needed to strengthen the evidence from this review.
1. Egger, M., Davey Smith, G., and Altman, D.G. (2003) Systematic Reviews in Health Care: Meta-analysis in context. Chapter 12; BMJ Books