The effect of an in-office bleaching agent with two different concentrations of titanium dioxide nanoparticles on the biaxial flexural strength, surface microhardness, and roughness of direct and indirect restorative composites

This study evaluated the impact of in-office bleaching treatments incorporating titanium dioxide nanoparticles (TiO₂NPs) on the mechanical properties of three universal nanohybrid composite materials: Grandio Direct, Grandio Indirect, and Admira Fusion. The investigation focused on flexural strength, surface roughness, and microhardness after bleaching with Opalescence Boost (40% hydrogen peroxide) alone and in combination with 5% or 10% TiO₂NPs. A total 360 discs, 120 composite discs for each carried on test, (n=10 per group) were prepared and subjected to four bleaching protocols: no treatment (control), Opalescence Boost only, and Opalescence Boost combined with either 5% or 10% TiO₂NPs. After treatment, samples were stored in artificial saliva before testing.
Statistical analysis using two-way ANOVA revealed significant interactions between composite type and bleaching treatment for biaxial flexural strength and surface roughness (p<0.001). For microhardness, only main effects were significant. Grandio composites (direct and indirect) exhibited significantly higher hardness than Admira Fusion. The addition of 5% TiO₂NPs (Group 1) preserved surface roughness and maintained a bleaching effect comparable to the bleaching agent alone (Group 2), whereas 10% TiO₂NPs (Group 3) offered no additional benefit.
In conclusion, incorporating 5 wt% TiO₂NPs into an in-office bleaching agent provided a comparable whitening result to conventional bleaching without adversely affecting surface texture or mechanical properties. However, increasing the TiO₂NP concentration to 10 wt% did not further enhance outcomes and may not be clinically beneficial. These findings suggest that lower concentrations of TiO₂NPs can improve the safety profile of bleaching treatments on dental composites.