[Evaluation of the critical surface tension (gc) of composite resins]

The purpose of this study was to assess the surface free energy of a series of composite resin restorative materials, utilizing the concept of critical surface tension (yc). Cylindrical samples of 20 mm diameter and 2 mm in thickness were prepared from 4 microfilled, 3 hybrid and 6 small particle composite resins. The critical surface tension was determined by contact angle measurements on 1000 grit ground surfaces. A Zisman series of homologous liquids was used (Water, Glycerol, Formamide, Thiodiglycol, Dilodormethane, I-Bromonapthalane). The recorded yc means were 30.000-42.600 dyn/cm for microfilled, 42.47-44.68 dyn/cm for hybrid and 42.19-49.20 dyn/cm for small particle composites. In all the cases the work of wetting was primary attributed to non polar and dispersion forces. The type and the concentration of the reinforcing fillers is the major factor influencing yc, especially in the presence of hydrophylic particles like Ba. Microfilled materials showed decreased wetting efficiency. Hydrophobic monomers do not provide any significant advantage on the wettability of polished composite surfaces.