Fracture toughness determination of composite resin and dentin/composite resin adhesive interfaces by laboratory testing and finite element models

Abstract

Objectives. The reliability and validity of the adhesive bond toughness of dentin/composite resin interfaces were studied from the standpoint of fracture mechanics. Methods. The fracture toughness ( K IC) and fracture energy ( J IC) values of two different composite resins (Brilliant Dentin and P50) were determined by using single edge notch (SEN) specimens loaded in three point bending and the results were analyzed by the t-test method ( p<0.1). The fracture loads of dentin/composite resin interface with different initial crack lengths were obtained experimentally. The adhesive fracture energy ( J adh), residual fracture energy ( J res) and effective (total) fracture energy ( J eff) for the symmetrical bimaterial (SBM) joint specimen for dentin/composite resin interfaces were calculated and the applied fracture energy ( J appl) values under the mastication force were obtained for the axisymmetric tooth models. All numerical calculations were carried out by the finite element method and software programs were prepared according to fortran 77. Results. The fracture toughness and energy values obtained experimentally for Brilliant Dentin were found to be higher than those for P50. It was seen that, calculated J values ( J adh and J res) changed with the crack length; but the effective fracture energy ( J eff) was independent of the crack length, as expected. The applied fracture energy ( J appl) and effective fracture energy ( J eff) are considerably smaller than the experimentally determined J IC values of composite resins. Significance. The bonded interface tends to produce microscopic flaws which could act as critical stress risers promoting interfacial failures. The initiation and propagation of such flaws under the mastication forces can be followed by fracture toughness ( K IC) or fracture energy ( J IC) in linear elastic fracture mechanics (LEFM).