Efeito da proporção entre BisGMA e TEGDMA nas propriedades de cimentos resinosos experimentais de dupla ativação

Abstract

A reduction on shrinkage stress of resin cements, associated to maintenance of their mechanical properties, can to favor the longevity of adhesively luted indirect restorations. It has been demonstrated that the delayed light-activation of dual-cured resin cements is able to reduce post-gel shrinkage. However, the same studies showed that the effects of this delayed light-activation on the mechanical properties are material-dependent, despite the effects of each component remains unclear. Thus, the aim of this study was to evaluate the effect of monomeric ratio on mechanical properties, viscosity, polymerization kinetics and shrinkage stress of dual-cured resin cements light-activated immediately or 05 min after its manipulation. Experimental resin cements were obtained with the monomers BisGMA and TEGDMA used in ratios of 1:1, 1:2 or 1:3 (in weight). After the viscosity measurement of each experimental material, bar-shaped specimens (25 x 2 x 2 mm) were prepared, while the light-activation of cements was performed immediately or 5 minutes after the insertion of cement into mold. Specimens were submitted to three-point bending test to measure flexural strength and elastic modulus. After the fracture, the Vicker‟s hardness of these specimens was measured. To analyze the post-gel shrinkage, the cements were placed over the biaxial strain-gauges, light-cured (immediately or after 5 minutes) and the strain was measured. Data were submitted to 2-way ANOVA (one-way for viscosity) and Tukey‟s test (α = 0.05). The ratio 1:1 resulted in a more viscous cement; and 1:3 in a more flowable. The experimental conditions did not affect the values of flexural strength. Irrespective of the light-curing moment, the cement at ratio 1:3 showed the lowest elastic modulus, while there was not difference between the other cements. Highest values of harness were found at the ratio 1:3 for the immediate light-curing and 1:2 for the delayed one. Except for ratio of 1:2, the immediate light-activation resulted in highest values of hardness. Irrespective monomeric ratio, immediate light-activation resulted in higher values of post-gel shrinkage. Considering its interaction with the light-curing moment, the monomeric ratio only affected the hardness of experimental dual-cured resin cements.