4 Effect of thermocycling on flexural strength of universal composites

Purpose The aim of this study was to evaluate the effect of thermocycling on flexural strength (FS) and flexural modulus (E) of different universal resin composites with a simplified shade system for direct restorations. Methods 120 bar-shaped specimens with dimensions 25x2x2mm were prepared with a stainless-steel matrix using five different materials (n=20): TP - Tetric Prime (Ivoclar), GA - G-aenial A’chord (GC), NS - Neo Spectra ST HV (Dentsply), SS - SimpliShade (Kavo Kerr) and NO -New Ormocer (Voco). Half of the specimens for each material were subjected to 3,000 thermal cycles (WITH) and the rest did not receive additional treatment (WITHOUT). The specimens were tested until failure using a universal testing machine, at a speed of 1mm/min, following the ISO 4049 specifications for the three-point bending test. The values of FS (MPa) and E (GPa) for each material were obtained and analyzed by two-way ANOVA (kind of resin x thermocycling) and Tukey test. Results ANOVA showed significant differences for the kind of resin (p=0.001) and thermocycling (p=0.001) for FS and E. The results of Tukey’s test for the factor kind of resin were: FS: GA-84.56(10.24)a, TP-102,1(7.77)b, SS-110.02(12.11)b, NO-110.24(11.37)b, NS-112.91(10.37)b. E: GA-8.18(0.45)a, TP-8.72(0.30)b, NS-9.13(0.32)c, SS- 10.24(0.34)d, NO-10.44(0.57)d. The results of Tukey test for the factor thermocycling were: FS: WITHOUT-109.35(14.05)b, WITH-98.59(13.22)a. E: WITHOUT-9.21(0.9)a, WITH-9.48(1.01)b. Conclusion The thermocycling reduced the FS but increased the E. For FS composite G-aenial A’chord showed the smallest means, while the others were similar. For E, the composites SimpliShade and New Ormocer showed the higher values.