Microshear Fatigue Testing of Tooth/Adhesive Interfaces

Purpose: The objective of the present study was to determine the fatigue resistance of several contemporary dentin adhesives as well as a resin-modified glass-ionomer cement. Materials and Methods: Cyclic loading of the adhesive interface was achieved by a microshear fatigue setup following a staircase approach, where the stress level at which 50% of the specimens fail after 104 cycles was calculated as the median microshear fatigue resistance (µSFR). Results: For all products tested, the µSFR was lower than the microshear strength. A wide spread in µSFR was observed, ranging from 24% to 76% of the quasi-static microshear strength, irrespective of the type of adhesive used. Conclusion: The results of this study show that the microshear test setup is a discriminative and reproducible way of testing tooth/adhesive interfaces, even at relatively low stresses. The results clearly indicate that such interfaces are vulnerable to progressive damage by cyclic loads. Further, at present there is not one bonding approach, whether "total etch" or "self-etching", that consistently yields higher fatigue resistance: the product factor seems to be of primary importance. Keywords: fatigue, dental adhesive, dynamic testing