Effect of filler content of restorative resins on retentive strength to acid-conditioned enamel.

In this in vitro study the retentive strength of enamel, either conventionally etched with a phosphoric acid gel or conditioned with an oxalic acid containing etching agent, was investigated. Five experimental restorative resins with filler contents between 0 and 78% by weight were polymerized on the etched enamel surfaces. In spite of the pronounced micromorphological differences of the patterns generated with the two etching agents, the bond strengths mediated were very similar. Application of an intermediate low-viscous or adhesive resin had no influence on bond strength. Exponential relationships were found between the filler content of the resins on the one hand and their flexural moduli and flexural strengths on the other. Significant exponential relations were also demonstrated between filler content and bond strength to the etched enamel surface. The linear relationship between mechanical properties of the resins and their bond strengths to etched enamel indicates that debonding occurred by cohesive failure in resin.