Influence of specimen designs on microtensile bond strength to dentine

Objectives: This study examined the influence of three specimen designs on the Microtensile Bond Strength (µTBS) of a self-etching dentine bonding agent (DBA) utilizing Finite Element Analysis (FEA). Methods: Fifty freshly extracted bovine central incisors were divided into three groups. Occlusal enamel was removed and the exposed dentine surface polished with # 600-grit SiC papers. Adper Prompt L-Pop (3M ESPE) was bonded to the dentine surface according to the manufacturer's instructions. A 6 mm thick layer of resin composite (Filtek Supreme 3M ESPE) was built up incrementally. After 24 hours water storage at 37˚ C, the teeth were sectioned vertically into 30 stick shaped specimens (1.2x 0.9 mm X-section, 12-13 mm Long). In the second and the third groups the teeth were sectioned and then trimmed into dumbbell and hourglass shapes of approximately 1 mm2 X-sectional area at the bonded interface (n=30). The specimens were subjected to µTBS testing at a cross-head speed of 0.5 mm/min. The fracture surfaces were examined using optical microscopy and SEM to determine the modes of failure. FEA models of the three designs were developed using MSC-MARC programme. A nominal load of 100 N was applied and the resultant stresses as the bonded interfaces were examined. Results: One-way ANOVA and Tukey's test revealed no significant differences in the µTBS for the Stick, Dumbbell and Hourglass specimens, which were 26.2 MPa ±9.3, 27.2 MPa ±6.8 and 25.6 MPa ±7.8 respectively (P>0.05). FEA results confirm experimental findings as no major differences in stress distributions at the adhesive interfaces were apparent for the three designs. The modes of failure were consistent with the expectations from the FEA analyses. Conclusion: The three different specimen designs had no influence on the µTBS of a self-etching primer to bovine dentine.