Objectives: To determine the efficacy of a miniaturized dumbbell test procedure designed to more easily identify defect(s) in bonded dentine test specimens.
Methods: Extracted human dentine substrates were pre-conditioned with 10-3 solution for 10, 30 or 60 s prior to dentine bonding with 4-META/MMA-TBB resin. Miniaturized dumbbell-shaped test specimens were prepared from the resin bonded samples. After 24 h storage in 37 degrees C water, the specimens were tensile-loaded to failure. Fractured surfaces and cross-sections were examined and compared under scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Results: Cohesive failure within the bonding resin was observed in specimens pre-conditioned for 10 s. The tensile bond strength of these was excellent. Bond strengths of specimens that were pre-conditioned for 30 and 60 s were significantly lower, and defects in these specimens, formerly difficult or impossible to identify, were readily identified under SEM and TEM microscopy.
Conclusion: The proposed method of tensile stressing to failure and microscopically examining fractured miniaturized dumbbell-shaped test specimens is a simple and reproducible test procedure. The protocol is capable of clearly elucidating defective resin infiltration of demineralized dentine in bonded interfaces. These defects are difficult to visualize by conventional and/or ISO recommended methods.