The effects of adhesive thickness on polymerization contraction stress of composite

A layer of an unfilled adhesive resin placed between the tooth and composit e restoration has been shown to absorb some of the stress generated in the composite during polymerization and to reduce interfacial leakage. The obje ctives of this study were to measure the change in polymerization contracti on stress of bonded composite as the thickness of the resin adhesive was sy stematically varied, and to correlate the effects of the adhesive thickness and reduced stress on marginal leakage in class V cavities. The maximum co ntraction force of composite (Herculite XRV) was measured in a tensilometer as the thickness of the adhesive bonding agent (Scotchbond MP) was Varied from 20 to 300 mu m. Composite was placed in Class V cavities prepared on t he labial surfaces of bovine teeth to which different thicknesses of adhesi ve had been applied by layering, and a marginal leakage test was performed by means of staining with silver nitrate. Contraction stress decreased sign ificantly as the adhesive thickness was increased. This result was supporte d by a theoretical examination of the data. In class V cavities, additional adhesive layering in the marginal area reduced the overall degree of micro leakage. The contraction stress generated during the placement of a composi te restoration contributes significantly to early marginal leakage, and thi s stress was significantly absorbed and relieved by the application of an i ncreasing thickness of low-stiffness adhesive.