Critical Evaluation of Adhesive Test Methods Used in Dentistry

Through the years, numerous articles dealing with dental adhesives have been published in the dental literature. A critical comparison of such articles reveals large differences in measured values, differences that not only seem to be between products, but also between different research groups. Because of these differences, the objective of this paper was to critically review some fundamental aspects of adhesion, and relate those aspects to dental adhesive studies. The outcome of that review was not very encouraging, because research, particularly in fields such as mechanical engineering and physics, does not support the notion of an overall adhesive strength value as we usually define in dentistry. Instead, adhesive studies should approach the problem from a fracture mechanics point of view rather than from an overall strength point of view. This review reveals that it is time to abandon traditional strength testing and move toward an increased use of fracture toughness tests and fatigue tests. Having said that, it is also important to realize and accept that as long as we do not have strong evidences correlating clinical success with any particular adhesive test method, in vitro tests should not be used as predictors of clinical performance. Only when we have reliable correlations between in vitro test results and clinical performance such methods will have any practical meaning.