Composite resin color change after vital tooth bleaching.

Color change of composite resin was determined with the Minolta Chroma meter (CR-100) after four sessions of vital bleaching. Specimens of selected composite resin materials were subjected to vital bleaching (37% H3PO4/1 minute, then 30% H2O2/infrared light/30 minutes.) Specimens were stored in water between bleaching. Control specimens were used to determine the effects of water storage alone. Initial L*a*b* color readings were made on 24-hour hydrated specimens. Final L*a*b* readings were made on 24-hour hydrated specimens. Calculations were made for the delta E values for each specimen. Mean delta E values and standard deviations were obtained for each material. Two-way ANOVA and Newman-Keuls analyses showed significant (alpha = 0.05) color change for most bleached materials. Additionally, some materials had delta E values greater than 3. These were visibly lighter compared to their controls. Vital bleaching produced color change in most composites as measured with the Chroma meter. This technique may be used to lighten dark-colored or stained composite resin restorations.