Efeito do envelhecimento em ácido cítrico na microdureza e resistência à flexão de resinas compostas

Objectives: To evaluate the influence of citric acid aging on the microhardness and flexural strength of three composites resins. Materials and methods: 15 specimens of each microhybrid composite resin (1- Suprafil-R&S, 2- Proclinic-PM, 3- Tetric-EvoCeram) were prepared. After light curing specimens were randomly assigned to 3 protocols of aging (A- bi-distilled H₂O pH = 6.6, immersion for 10 days; B- immersion for the first 24h in bi-distilled H₂O pH = 6.6, followed by 9 cycles of 6h in citric acid pH = 2.5 interchanging with 18h of bi-distilled H₂O pH = 6.6; C- immersion for 6h in citric acid pH = 2.5 interchanging with 18h of bi-distilled H₂O pH = 6.6, followed by 24h immersion in bi-distilled H₂O pH = 6.6). Therefore all the 9 experimental groups (n=5) were submitted to an ageing period of 10 days. The specimens were then submitted to Vickers microhardness test and flexural test. Data were analysed with ANOVA and Student-Newman-Keuls post-hoc test. Results: The scheme of aging C and the Proclinic-PM composite recorded statistically lower microhardness values (p<0,05) than the other. Flexural strength values were not influenced (p=0,42) by the scheme of aging, however Suprafil-R&S composite yielded statistically higher flexural strength values than the other composites (p<0,05). Conclusions: Exposure to citric acid immediately after light curing negatively influences the composite microhardness, but did not affect the flexural strength.