Effect of Preheating and Precooling on the Flexural Strength and Modulus of Elasticity of Nanohybrid and Silorane-based Composite

Statement of the problem: composite resin may be used in different temperatures; it is crucial to determine the effect of temperature on mechanical properties of nanohybrid and silorane-based composite.purpose: this in vitro study compared the flexural strength and modulus of elasticity of nanohybrid and silorane-based resin composite, at 4?c, room temperature (25?c), and 45?c.materials and method: in this experimental study, 60 specimens were prepared in a metal split mold (2×2×25mm). two different resin composites, filtek z250 xt (3m/ espe) and filtek p90 (3m/espe), were evaluated. the material were inserted into split molds at room temperature, 4?c or 45?c and cured with led (1200 mw/cm2) for 20 seconds in four points (n=10). then, a three-point bending test was performed using a universal testing machine at a crosshead speed of 0.5 mm/min for measuring the flexural strength and flexural modulus of samples. the data were analyzed by the two-way anova and tukey test (p < 0.05).results: the mean highest flexural strength was observed at 45?c, showing statistically significant difference with flexural strength at 4?c (p= 0.0001) and 25?c (p= 0.003) regardless of the type of resin composite. the flexural modulus at 45?c was highest, showing the statistically significant difference with flexural modulus at 4?c (p= 0.0001) and 25?c (p= 0.002). the flexural modulus was statistically different between nanohybrid and silorane-based resin composite (p= 0.01) in 25?c and 45?c, but there were no statistically significant differences between flexural strength of filtek z250 xt and filtek p90 regardless of the temperatures (p= 0.062).conclusion: preheating the resin composite at 45?c improves flexural strength and modulus of nanohybrid and silorane-based resin composite. however, flexural strength and modulus of the tested materials were not affected by precooling. the flexural modulus of nanohybrid resin composite was significantly higher than silorane-based resin composite in 25?c and 45?c temperatures.