Methods: 80 specimens were prepared for each brand of composite (Grandio SO/Voco-G, Amaris/Voco-A, Z350 XT/3MEspe-Z, P90/3MEspe-P) with 2 mm/thick and 2.8 mm/diameter. For each material, the specimens were divided into four groups according to the food-simulating substance used for chemical degradation (CD): artificial saliva (AS), heptane (H), citric acid 0,02M (CA), ethanol 70% (E). The specimens were kept in individual vials with 2 ml of each solution for 7 days at 37ºC. After this period, the top surface of composites were submitted to 10,950 brushing cycles in an automatic toothbrushing machine with an abrasive slurry, simulating a one year of clinical use. Surface roughness and microhardness measurements were obtained in different moments (MOM) from the specimens: at baseline (BL), after immersion for food-simulating (IM) an after TB. Data were submitted to statistical analysis with two-way repeated measures ANOVA and Tukey’s test.
Results: ANOVA showed significant differences in microhardness for COM, CD and MOM (p=0.00). The results of Tukey’s test were: COM:, A(64.47)a, P(69.03)a, Z(87.03)b, G(153.45)c. CD: H(87.61)a, E(93.35)b, C(95.75)b, AS(97.28)b; MOM: BL(93.78)a, IM(104.81)b, TB(81.90)c. ANOVA showed significant differences in roughness just for COM (p=0.03) and MOM (p=0.00). The results of Tukey’s test were: COM: P(0.15)a, G(0.19)ab, Z(0.20)ab, A(0.23)b. MOM: BL(0.24)a, IM(0.23)a, TB(0.11)b. The groups followed by the same letters did not show significant differences.
Conclusions: In relation to microhardness, the composite G has the highest mean and the heptane produced the biggest reduction. In relation to roughness, the food-simulating substances did not have a significant effect. The toothbrusing after the chemical degradation reduced the RA values.