Critical Analysis of the Influence of Different Parameters on the Microtensile Bond Strength of Adhesives to Dentin

Purpose: To evaluate how six different test parameters (TP) of the microtensile bond strength (µTBS) methodology influence the test outcome. Materials and Methods: The microtensile bond strength of adhesives bonded to dentin was measured, and the resultant failure patterns and stress-time graphs were analyzed, varying the µTBS specimen-fixation mode (TP1), the microspecimen geometry (TP2), the microspecimen bond surface area (TP3), the remaining dentin thickness of the microspecimens (TP4), the procedure employed to glue the microspecimen to the µTBS jig (TP5), and the µTBS crosshead speed (TP6). Results: The orientation of the microspecimens to the actual interface primarily influenced the resultant µTBS value and the eventual failure pattern. A notched jig consistently yielded significantly higher µTBS values than samples fixed onto a flat jig or following a "top-bottom" design (TP1). A higher bond strength, a lower standard deviation/coefficient of variation, a failure closer to the interface, and a more representative number of specimens per tooth were obtained for nontrimmed, square microspecimens (TP2). The most reproducible results were obtained using square specimens of 1 mm2 (TP3), which could also be most easily prepared. The remaining dentin thickness (TP4) was an influential factor as well, whereas the microspecimen gluing protocol (TP5) and the crosshead speed (TP6) appeared less influential. Conclusion: As several test parameters significantly influenced the µTBS outcome, sufficient attention should be paid to these methodology variables with regard to the µTBS-test reliability and reproducibility. Parole chiave: microtensile bond strength, test methodology, test parameters, bonding, dentin