Colour stability of visible light-curing hybrid composites.

The colour stability of six visible light-curing fine hybrid composites was evaluated after 24 and 120 hours of irradiation using a xenon lamp. Discoloration of four shades of each material (A1, A2, A3.5 and B2- Vita shade guide) was measured using a reflection spectrophotometer with the CIE-L*a*b* system. The discoloration after 24 hours of irradiation had values of between 0.7 and 3.8 DE*, and was therefore, with the exception of Z 100 (colours A1 and B2), clinically acceptable. The results showed that the differences in colour of all shades of Pekafill NF and Tetric tested were significantly less than those of the other products. All samples, with the exception of Pekafill NF (A3.5 and B2), showed increased discoloration to values of 3.7 to 7.8 DE* after 120 hours of exposure to UV light. In general, all the composites tended to become more yellow (b*), darker (L*) and slightly greener (a*).