Comparative evaluation of the effect of bleaching agent on color change of single-shade vs. bulk-fill composite resin: an in vitro study

Introduction
Aesthetic success in restorative dentistry relies heavily on achieving color harmony between restorations and natural teeth. Single-shade composites utilizing smart chromatic technology and the chameleon effect, offer simplified shade matching compared with multi-shade systems. This study evaluated the color stability and adaptability of single-shade composite post-bleaching and compared them with a bulk-fill composite.

Material and methods
Thirty composite discs were fabricated and divided into two groups: Group 1 (Vittra APS Unique single-shade composite) and group 2 (Tetric N-Ceram Bulk-Fill composite), with 15 samples in each group. All specimens underwent thermocycling to simulate oral conditions, and were then bleached using 40% hydrogen peroxide (Opalescence Boost) in three 15-minute sessions. Color measurements were recorded before and after bleaching using CIELAB color system via a spectrophotometer. Data were analyzed with Wilcoxon signed-rank and Mann-Whitney U tests for non-parametric distribution.

Results
Both groups showed a decrease in mean color values and became lighter after bleaching. The changes in color parameters within each group were not statistically significant. The difference in ΔE values between the two groups was significant (p = 0.002), with the single-shade composite exhibiting a greater overall change.

Conclusions
Single-shade composite resin demonstrated superior adaptability to post-bleaching shade changes compared with the bulk-fill composite. This suggests its potential for improved aesthetic outcomes in restorative procedures following tooth whitening, possibly reducing the need for restoration replacement.