A TENSILE TEST TO FACILITATE IDENTIFICATION OF DEFECTS IN DENTIN BONDED SPECIMENS

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-c onditioned with 10-3 solution for 10, 30 or 60 s prior to dentine bond ing with 4-META/MMA-TBB resin. Miniaturized dumbbell-shaped test speci mens were prepared from the resin bonded samples. After 24 h storage i n 37 degrees C water, the specimens were tensile-loaded to failure. Fr actured surfaces and cross-sections were examined and compared under s canning electron microscopy (SEM) and transmission electron microscopy (TEM). Results: Cohesive failure within the bonding resin was observe d in specimens pre-conditioned for 10 s. The tensile bond strength of these was excellent. Bond strengths of specimens that were pre-conditi oned for 30 and 60 s were significantly lower, and defects in these sp ecimens, formerly difficult or impossible to identify, were readily id entified under SEM and TEM microscopy. Conclusion: The proposed method of tensile stressing to failure and microscopically examining fractur ed miniaturized dumbbell-shaped test specimens is a simple and reprodu cible test procedure. The protocol is capable of clearly elucidating d efective resin infiltration of demineralized dentine in bonded interfa ces. These defects are difficult to visualize by conventional and/or I SO recommended methods. (C) 1998 Elsevier Science Ltd. All rights rese rved.