Influence of Thermocycling on Microhardness of Indirect Resins

Objectives: To evaluate the thermocycling effect on microhardness of laboratory composite resins. Methods: 30 disks were fabricated, 5 mm of diameter and 2mm of width, using 3 laboratory resins (n=10): Gr1- Resilab Master (Wilcos/Brasil), Gr2 - Vita VMLC (VITA Zahnfabrik/Germany) and Gr3 - Vita Zeta (VITA Zahnfabrik/Germany). Vickers microhardness of all specimens (sps) was evaluated using a microhardness tester FM-700 (Future Tech- 50 g/10s). The sps were measured before and after the thermocycling (3.000 cycles and 12.000 cycles - 5°/55°C±10). The data (Kg/mm2) were statistically analyzed using ANOVA and Tukey's test (5%). Results: The microhardness values before cycling were (mean±SD): Gr1:55.50±4.6; Gr2: 35.54±2.5; Gr3:27.97±1.6. After 3.000 thermocycles, the data obtained were: Gr1: 55.54±3.9; Gr2: 29.92±2.73; Gr3:21.01±1.4. After 12.000 cycles, the values obtained were: Gr1:54.27±3.2; Gr2: 30.91±1.6; Gr3: 23.81±0.9. Variance analysis (ANOVA) and Tukey's test revealed that Gr3 presented the lowest microhardness values compared with Gr1 and Gr2 (p<0.05), which didn't differ between them (p>0.05). Conclusions: It can be concluded that after thermocycling, the laboratory composites resins decrease their microhardness.