Taking time to gather evidence

Article Outline

• Background
• Material Evaluations
• Implications
• Copyright

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Background 

Evidence-based dentistry is being widely encouraged, with whole systems developed to rate the hierarchy of evidence. One aspect that has been left out is time, which is especially important in evidentiary research dealing with dental materials and techniques. Often conclusions regarding dental materials and techniques are based on simple trends that are drawn from underpowered clinical trials, case reports, or in vitro research. However, speakers at various venues regularly present information as if it is proven doctrine. Three examples are offered to convey the importance of considering the effectiveness of materials over time.

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Material Evaluations 

Restoring endodontically treated teeth often involves the use of an endodontic dowel or post to help retain the core material on which the crown will eventually be made. Stiff metal dowels that are prefabricated or custom fabricated as a cast post and core are the traditional choice, but flexible dowels were developed that would flex along with the tooth. If fracture occurs, the mode of fracture would be less catastrophic than what occurs with stiff dowels. Flexible dowel clinical trials were first published in the late 1990s, and the failure rate after 30 months was found to be 2%, an outstanding result. However, a follow-up evaluation a mean of 6.7 years later found the failure rate was a dismal 35%.

Another study focused on the self-etching adhesive Prompt-L-Pop. Evaluating the retention of restorations in class V noncarious cervical lesions, retention was 96% after 6 months but decreased to 81% after 2 years. The high failure rate prompted the discontinuation of the study at that point. Results of a second study of the same material yielded retention rates of 76% at 6 months and 65% after 1 year.

The third example involves all-ceramic materials. It was proposed in 1998 that clinicians should have available data from independent clinical trials lasting at least 5 years before using any new all-ceramic materials. These data should document a survival rate of at least 95%. This long period is essential with all-ceramic crowns because they tend to fail through progressive defect and crack propagation and cause significant financial and emotional costs with these premature failures. None of the all-ceramic materials available has been able to completely meet these criteria for molar crowns or for 3-unit fixed partial dentures, even though they are widely touted as the best materials for dentists to use.

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Implications 

New materials are being introduced to the dental profession at a high rate, many with only in vitro testing of their physical properties and little or no predictive value relevant to long-term performance. As a result, the practicing dentistry community becomes the test ground for these materials. If too many practitioners complain, products are quietly removed from the marketplace. The marketing of many of these new materials has become highly aggressive, making dentists feel that they are being left behind if they don’t begin using the new stuff. Academicians are also placed in this predicament. It is more responsible to rely on time-proven materials and techniques, which is in line with the emphasis on evidence-based dentistry.