A Microshear Test to Measure the Bond Between Dental Composites and Dental Substrates.

Introduction: In order to determine the real efficacy and durability of polymeric dental adhesives, thorough clinical testing is necessary. However, in practice, long-term clinical testing is expensive and commercial adhesive materials are constantly undergoing change so that the clinical testing necessary to evaluate their long-term properties and success rates (typically four years) becomes impractical. Thus, there is the need for reliable laboratory tests to serve as screening tools to identify promising new dental adhesive systems and improvements to existing systems. Adding to the challenge is the very complex conditions that a tooth cavity presents to achieving effective adhesion of the restorative material to this heterogeneous mineralized substrate. The mineralized tissues of the tooth, enamel with its prismatic rod-like apatitic structure and dentin with its array of dentin tubules, are both anisotropic materials that present variable substrates for adhesive systems. Depending upon the orientation of the rods and tubules with respect to the adhesive interface, variations in bond strength would be expected. The polymeric adhesive restorative, a viscoelastic material, is constantly exposed to a hostile, multichallenging milieu comprising masticatory stresses, aqueous fluids that can initiate chemical attack, and cyclic exposure to heat and cold. This list of factors that can affect adhesion to tooth structure is not meant to be exhaustive but rather illustrates the complex nature of properly assessing the bond between the restorative and the mineralized tissue, and illustrates the challenge involved in designing a reliable screening test.