Color changes of dental resin composites by a salivary enzyme

The objective of this study was to evaluate the color change (DeltaE(ab) (*)) of dental resin composites immersed in a salivary enzyme of esterase (ETE, porcine liver esterase, 400 mU/ml) compared to those immersed in phosphate-buffered saline (PBS). The colors of three brands of resin composites of 13 shades were measured after polymerization and polishing with 1500-grit SiC paper and after immersion in PBS or ETE up to 9 weeks. Color was measured according to the CIELAB color scale. DeltaE(ab) (*)after immersion was calculated by the equation DeltaE(ab) (*) = [(DeltaL(*))(2) + (Deltaa(*))(2) + (Deltab(*))(2)](1/2). Surface roughness (Ra) and Vickers hardness number (VHN) were measured. DeltaE(ab) (*)values after immersion in ETE was not higher than those in PBS. Immersion in solutions more than 3 weeks resulted in perceivable color changes (DeltaE(ab) (*) > 3.3) in one material, and immersion in solutions up to 9 weeks resulted in not-perceivable color changes in the other materials. Discoloration generally increased as the immersion period increased. For one composite, the value increased abruptly in the period of 3 days to 3 weeks of immersion. The change in Ra value after immersion was varied by the composite and shade. VHN decreased significantly after immersion in ETE for nine weeks. Immersion in PBS resulted in decreased VHN in two composites.