Effect of Preheating on The Flexural Strength of Composite Resins

Objectives: At room temperature composite resins are viscous and this condition may effect the ability of the materials to flow and adapt to preparation walls. The purpose of this study was to compare the flexural strengths of two commercial resins, at room temperature and preheated prior to light polymerization with standard and step-cure protocols. Methods: One nanohybrid (Grandio, VOCO, Cuxhaven, Germany), and microhybrid composite resin (Filtek Z250, 3M ESPE, St. Paul, MN, USA) were used. The materials were inserted into rectangular bar shaped moulds at room temperature or preheated to a temperature of either 40, 45 or 50 °C and cured with standard or step-cure protocols with high intensity halogen (Elipar Highlight, 3M-ESPE, St. Paul, MN, USA). Ten specimens were prepared for each preheating and light curing protocol. A three-point bending test according to ISO 4049 was performed using an Universal testing machine at a crosshead speed of 1 mm/min. The data were analyzed by one way analysis of variance and Tukey post hoc tests (p < 0.05) to examine the effect of curing protocol and preheating. Pearson's correlation test was used to determine the correlation between flexural strength and preheating. Results: ANOVA revealed no statistically significant difference (p>0.05) between flexural strengths of the materials, curing protocols and temperature of the materials. No significant correlation was found between preheating and flexural strength. Conclusion: The results of this study showed that neither preheating nor curing protocols did not changed the flexural strength of the materials tested. So it could be concluded that the materials could be preheated to adapt more to the cavity walls.