Effect of mechanical properties of resin composites on the efficacy of thedentin bonding system

This study determined the relationship between marginal adaptation to denti n cavity preparations, tensile bond strength of the restorations, and mecha nical properties of the composites. Contraction gaps, tensile bond strength s, flexural strengths, and Young's modulus of eight commercial resin compos ites were determined. Eight resin composites (Clearfil AP-X, Estelite, Esti o LC, Litefil II-A, Prodigy, Progress, Silux Plus, and Z100) were applied t o dentin cavities or flat dentin surfaces mediated with an experimental den tin bonding system consisting of 0.5M EDTA dentin conditioner, priming with 35% glyceryl monomethacrylate solution, and a commercial dentin bonding ag ent application (Clearfil Photo Bond). The contraction gap of the resin com posite in a cylindrical dentin cavity was prevented completely for three of the resin composites tested (Clearfil AP-X, Estelite, and Silux Plus). The measured tensile bond strength correlated significantly not only with the tensile strength(r(2) = 0.506; 0.01 < P < 0.05), but also with the flexural strength (r(2) = 0.871; P < 0.001) and Young's modulus (r(2) = 0.712; 0.00 1 < P < 0.01) of the composites, whereas the contraction gap did not correl ate significantly with the measured tensile bond strength, the tensile stre ngth, the flexural strength, or Young's modulus (P > 0.05). However, the re sults did indicate that the higher tensile bond strengths measured in the t raditional test may be related to the higher mechanical properties of the r esin composites because of the number of specimens that exhibited cohesive failure.