Influence of different storage media on the microhardness of composite resins

Resumo

The longevity of composite resins is strongly influenced by the intrinsic characteristics of materials and by the environment to which they are exposed. The objective of this study was to evaluate the effect of different storage media on the microhardness of composite resins for direct restorations. The composite resins tested were: Durafill® VS – Heraeus Kulzer (microparticle), Filtek™ Z250 - 3M ESPE (microhybrid), and Filtek™ Supreme - 3M ESPE (nanoparticle). Twenty-five standard-format disc-shaped specimens were prepared for each material, and were randomly distributed into five groups (n=25). Specimens were kept in 5 different storage media (dry, 25%, 50%, and 100% alcohol solutions, and distilled water) at 37ºC for one week. Knoop microhardness measurements were made with a microdurometer (10gf / 10sec) in two time intervals: immediately after specimen preparation, and again after seven-day storage in the different media. Data were analyzed using ANOVA and the Tukey test at 5% level of significance. The wet storage media had a distinct influence on the microhardness of composite resins evaluated. The nanoparticle resin showed greater loss of microhardness when submitted to alcoholic media in comparison with micro-and microhybrid resins, which was significant only when submitted to the 100% alcoholic medium. The composite resins evaluated showed good behavior in relation to the microhardness.