Comparison of an analytical expression of resin composite curing stresses with in vitro observations of marginal cracking

Abstract

PURPOSE: To observe the marginal failure at the enamel-resin composite interface upon curing, and utilize a recently developed analytical model for curing stresses to relate to the extent of interfacial failure. METHODS: Occlusal cavity preparations were restored with Heliomolar, Filtek Z100 or UltraSeal XT Plus resin composites. Teeth were restored with either bulk or incremental placement. The control group was not restored. Teeth were placed in an acrylic ring and embedded in cold mounting epoxy resin and the crown sectioned so that the tooth/restoration interface and cavosurface margin could be visualized with an optical microscope. A recently developed simplified analytical approach was utilized to evaluate the composite-enamel interface tensile stresses for these materials theoretically and thereby the fracture susceptibility of the resin-enamel interface during polymerization. RESULTS: White lines, enamel cracks and interfacial failure of the bond were evident for all three materials evaluated (P < 0.01). Gaps at the enamel-composite interface measured 1-10 microm and were more evident for Ultra Seal XT Plus and Z100 than Heliomolar. Conversely, cracking of the enamel adjacent to the interface was more evident for Heliomolar. Statistical analysis showed that enamel cracking and interfacial failure was significant for all groups (P < 0.01). An inverse relationship was noted between enamel cracking and interfacial failure (P < 0.05). The predictions for the extent of cracking from the mathematical modeling match the experimental data and prior studies.