Comparative evaluation of two different concentrations of carbamide peroxide-based bleaching gel on the surface hardness of nanohybrid and bulk-fill composites: An in vitro study

ABSTRACT Context: Microhardness is a crucial factor in determining the long-term prognosis of a tooth. Composite restoration is a common dental procedure aimed at improving the aesthetics of anterior teeth. However, dental fluorosis can create challenges in shade matching, making it essential to bleach the tooth before proceeding with composite restoration. Aim: This study aims to evaluate and compare the microhardness of bulk-fill and nanohybrid composite resins after being treated with 16 and 22% carbamide peroxide gel in an in vitro setting. Materials and Methods: Sixty composite specimens were fabricated using custom-made Teflon molds. These specimens were divided into two main groups: Group A (bulk fill) and Group B (Nanohybrid), with each further subdivided into three subgroups of ten specimens. The subgroups were classified based on the concentration of carbamide peroxide used for bleaching—16%, 22%, and a control group with no bleaching. After undergoing a two-week home bleaching treatment following standard protocols, the specimens were subjected to Vickers hardness testing to measure their microhardness. Statistical analysis was conducted using descriptive statistics, one-way ANOVA, and a post hoc test. Results: The findings revealed a statistically significant reduction in microhardness for both composite types after bleaching. However, nanohybrid composites exhibited superior microhardness compared to bulk fill composites. Conclusion: Home bleaching treatments lead to a decrease in the microhardness of composite materials, with the concentration of the bleaching agent playing a significant role in the extent of this reduction.