Avaliação dos parâmetros críticos do ensaio de microtração: análise laboratorial e por Elementos Finitos

Abstract

Objectives: Innumerous modifications have been made in the microtensile methodology since its introduction. The aim of this study was to evaluate the effect of critical parameters such as specimen geometry, microtensile device, fixation mode and bonding interface contamination on bond strength, failure mode, and stress distribution of an adhesive system to human dentin. Materials and Methods: Twenty-one extracted human third molars were ground to expose occlusal dentin, and after surface treatment with a total-etch 2-step adhesive system (Adper Single Bond II), composite resin restorations were constructed over the dentin. Dumbbell and stick-shaped specimens were fabricated from same teeth and divided into three microtensile gripping devices: Di- dumbbell-specimens placed onto Dircks device; GeS- stick-specimens gripped onto a Geraldeli s device with SuperGlue; GeZ- stick-specimens gripped onto a Geraldeli s device with Zapit. Specimens were tested and microtensile bond strengths were determined (MPa). The failure mode was examined under stereomicroscopy and fracture initiation sites were verified by scanning electron microscopy and energy dispersive spectroscopy. Three-dimensional models of each device and specimen were created and finite element simulations were performed. Results: The effect of the gripping devices on the bond strength was not significantly, but the failure mode was directly influenced by the type of device. Dircks device is less critical to human error than Geraldeli s device. The bonding interface contamination and regluing process increased the bond strength. Dircks device produced a more uniform stress distribution at the dumbbell specimen adhesive layer than did the Geraldeli s device at the stick specimen layer. Conclusions: The type of device and specimen geometry did not influence the bond strength values; however, the failure mode and the stress distribution of the specimens were affected by these parameters.