Effects of cyclic temperature changes on water sorption and solubility of composite restoratives

This study investigated the effects of cyclic temperature changes on the water sorption and solubility of four commercial composite resins (Silux Plus, Z100, Ariston pHc and Surefil). The methodology was based upon ISO 4049 procedures with modifications for specimen dimension and thermal-cycling. Eighteen disc specimens (10 +/- 1 mm diameter and 1 +/- 0.1 mm thick) were made for each composite and randomly divided into three groups. The specimens were stored in a desiccator maintained at 35 +/- 1 degrees C until a constant mass was achieved and treated as follows: Group 1--stored in distilled water at 356 degrees C for 178 hrs; Group 2--stored in distilled water at 35 degrees C for 173 hours and subjected to five hours of thermal-cycling with an upper temperature of 45 degrees C; and Group 3--stored in distilled water at 35 degrees C for 173 hours and subjected to five hours of thermal-cycling with an upper temperature of 60 degrees C. Mass after treatment was measured and specimens were re-conditioned to constant mass. The volume of the specimens was obtained and water sorption/solubility calculated. Data was analyzed using factorial ANOVA/Scheffe's post-hoc test at significance level 0.05. The effects of thermal-cycling on water sorption was material dependent. Thermal-cycling at an upper temperature of 60 degrees C significantly increased water sorption of Silux Plus. A significant increase in water sorption was also observed when Z100 was thermal-cycled at an upper temperature of 45 degrees C. The water sorption of Ariston pHc and Surefil was not affected by thermal-cycling. Thermal-cycling did not affect the solubility of all composites. For all treatment groups, Surefil had significantly lower water sorption than the other composites evaluated. The water sorption of Z100 and Surefil was significantly lower than Silux Plus and Ariston pHc.