Comparison of color changes and stability and surface topography of dental composites using four different bleaching methods

Abstract

the aim of bleaching is improving the esthetic appearance of discolored teeth however bleaching agents in contact with tooth- colored restorations cause changes in mechanical properties and color of the composite resin restorations that needs precise evaluation. The purpose of this study was to compare the color changes and stability and surface topography of dental composites using four different bleaching methods. Materials and methods: 72 discs 10mm in width and 1mm in height were prepared from composite resin with completely smooth surface. Specimens were kept in tea solution for three hours period for forty days. Then spectrophotometer was used to measure a, b and l indices of all the discs. Specimens were divided into four experimental groups (n=18 of each) and bleached as follows: G1: bleaching with %35 HP bleaching gel G2: bleaching with %35 HP bleaching gel and LED G3: bleaching with %35 HP bleaching gel and Nd:YAG laser G4: : bleaching with %35 HP bleaching gel mixed with graphite particles and Nd:YAG laser . After measuring the color indices once again color changes(E) were calculated by the CIELAB system. Specimens were kept in distilled water and room temperature for a month then color indices were measured again and E calculated to evaluate the color stability of specimens. Specimens were assessed by atomic force microscope (AFM) for surface texture evaluation. Data was analyzed with SPSS 18. Results: all groups after bleaching showed higher E value than control group(G1) .Nd:YAG +graphite showed highest color change. mean color changes (E) one month after bleaching in HP group was statistically significant in comparison with Nd.YAG and Nd:YAG +graphite groups (p<0.001).There were no statistically significant differences among other groups Surface roughness of all groups increased after bleaching but degree varied according to bleaching method. LED and Nd:YAG +graphite groups affected the most and Nd:YAG group the least as follows HP group. Conclusion: Based on the result of the present study it was concluded that light activation of the bleaching gel provided more intense bleaching than use of the bleaching gel without light activation. Addition of the coloring agent to bleaching gel improved the photothermal activation of bleaching gel which could then produce greater bleaching efficiency.Surface roughness of composite increased after bleaching.