Effect of preheating on the physicochemical properties and bond strength of composite resins utilized as dental cements: An in vitro study.

STATEMENT OF PROBLEM: Little is known regarding the use of preheated composite resins to bond indirect restorations and its impact on mechanical properties when compared with resin cements. PURPOSE: The purpose of this in vitro study was to compare the chemical and physical properties and bond strength to enamel and ceramics of preheated composite resins and resin cements. MATERIAL AND METHODS: Two composite resins, the microhybrid Filtek Z250XT and the nanoparticulate Z350XT were tested, and 2 commercially available resin cements, the dual-polymerized Rely-X ARC and the light-polymerized Rely-X Veneer were used as controls. A device (HotSet) was used to preheat the composite resins to 69 °C before light-polymerization. The following properties were tested: flexural strength, modulus of elasticity, fracture toughness, microshear bond strength to enamel and ceramics, degree of conversion, flow, sorption and solubility, and color stability. Statistical analysis was done with ANOVA and Holm-Sidak for multiple comparisons (α=.05). RESULTS: Preheating had no significant effect on the degree of conversion, flexural strength, fracture toughness, solubility, or microshear bond strength to the enamel of the tested composite resins (P>.05). However, preheating increased the sorption and reduced the microshear bond strength to the ceramic (P<.05). The flowability of the composite resins increased with heating but showed lower values when compared with both resin cements (P<.05). Color stability was more affected in the preheated composite resins than in the resin cements. CONCLUSIONS: The preheating process resulted in little to no benefit in the evaluated properties for the composite resins. Resin cements appear to be the best option for cementing indirect restorations.