In vitro evaluation of the bleaching effect on the change of color match of omnichroma composite resin

Aim To in vitro evaluate the bleaching effect on the color match of Omnichroma composite resin restorations to the teeth color. Materials and methods Thirty freshly extracted intact human premolars were collected and mounted in acrylic resin blocks (only roots were embedded). The shade of the selected teeth was measured by (VITA Easyshade V). Class V cavities (4 mm width, 2 mm length, and 2 mm depth) were prepared 2 mm coronal to cement-enamel junction on the cervical third of the facial surface of each tooth. Specimens were randomly divided into two equal groups ( n = 15): group I: was restored with nano hybrid Tetric N- ceram while group II: was restored with Omnichroma supra-nano filled composite resin using their respective adhesives. All the specimens were thermocycled for 500 cycles from 5 to 55°C with 15 s dwell time, and 20 s transfer time. The initial data of color measurements for tooth and restoration surfaces were recorded after thermocycling using VITA Easy Shade V. Specimens were then bleached using 40% HP by White smile power whitening YF according to the manufacturer instructions and kept in artificial saliva for 1 week before color re-measuring. All data were collected, tabulated, and statistically analyzed at 95% significance level using a software statistical package for social sciences (SPSS version 26). Results Before bleaching, higher mean ΔΕ values were recorded for the teeth (3.38 and 2.74) compared to (2.24 and 1.82) of the restorations in group I (Tetric N) and group II (Omnichroma) respectively with no statistically significant difference ( P = 0.26 and 0.43) in either of the groups denoting the color match between the restorations and the teeth in both groups. After bleaching there was a highly statistically significant difference ( P = 0.039) between the mean ΔΕ values of teeth (5.56) and restorations (3.23) in group I, denoting the color mismatch. While in group II there was no significant difference ( P = 0.249) between the values of teeth (5.25) and restorations (4.49) denoting the persistence of the color match after bleaching. No significant difference was found between the ΔΕ values of teeth used in both groups neither before ( P = 0.62) nor after bleaching ( P = 0.802). While there was a significant difference between the recorded values of the restorations after bleaching ( P = 0.026) although the difference was not significant before bleaching ( P = 0.619). Bleaching significantly affected the teeth color ( P = 0.013 and 0.038), and the restoration color ( P = 0.049 and 0.012) in groups I and II, respectively. Conclusions Omnichroma class V composite restorations matched the shades of teeth before and after bleaching where it was changed to a lighter shade with the teeth enamel that was within the acceptable clinical range. The color matching of the Tetric N restorations after bleaching was lost where the teeth were lighter in a clinically detectable manner, which necessitates restoration replacement.