Abstract
The strength of adhesion between tooth substance and composite resins, used as restorative material, was assessed by a push-out shear test, which simulated the force produced by mastication. A cylindrical cavity was created in each of four kinds of tooth substance. The cavity was then filled with composite resin. The test specimens prepared were then pressed to examine the adhesive strength of composite resin. The adhesive strength was highest for enamel, was lower for enamel/dentin and was lowest for dentin. The adhesive strength of enamel/dentin was much lower than that of enamel (45% lower when chemically-cured composite resin was used, and 29% lower when light-cured composite resin was used). This was probably because the adhesive area between the dentin reduced the adhesive strength. We then analyzed samples in which shear force was applied to the enamel/dentin test specimen. The apparent adhesive strength, obtained form theoretical calculation, tended to show a constant relationship to the strength actually measured. This suggests that the effective adhesive area of the dentin is smaller than area actually covered by the dentin. Furthermore, a gap, probably due to the effects of tensile stress, was observed in the adhesive interface between the composite resin and dentin. This gap seems to reduce the adhesive area, leading to a decrease in adhesive strength. Thus, the push-out shear test method appears to be useful in evaluating adhesive properties of composite resin.
