effect of different bleaching procedures on hardness and surface roughness of nanohybrid composite restorations

The survival of composite restorations largely hinges on two critical factors: surface roughness and microhardness. this study aimed to evaluate the individual and combined effects of home and office bleaching methods on these parameters in nanohybrid composite restorations.materials and methods: in this in vitro experimental study, 56 disc-shaped composite specimens (6 mm diameter and 3 mm thickness) were used. following polishing, they were randomly assigned into four groups (n=14 each): (i) control (immersed in distilled water), (ii) home bleaching with 22% carbamide peroxide (cp), (iii) office bleaching with 35% hydrogen peroxide (hp), and (iv) a combination of office and home bleaching. vickers hardness testing and surface roughness measurements using a profilometer were performed. to determine the differences among the study groups, a one-way analysis of variance (anova) was employed, followed by the bonferroni test for post-hoc pairwise comparisons, and statistical significance was considered at a p-value <0.05.results: group iv exhibited a significant reduction in microhardness compared to the control group (p-value: 0.05). furthermore, the surface roughness in group iv was notably higher than both the control and group ii (p-value= 0.05).conclusion: the study concludes that while individual home or office bleaching techniques do not significantly impact the surface hardness or roughness of composite materials, their combined application results in significant reductions in microhardness and increases in surface roughness. these findings underscore the need for careful consideration of bleaching techniques in dental practice, especially for patients with composite restorations.