Effects of Time-Elapsed Bleaching on the Surface and Mechanical Properties of Dentin Substrate Using Hydrogen Peroxide-Free Nanohydroxyapatite Gel.

Introduction: There is a critical need to address concerns surrounding the potential impact of bleaching gels specifically on the tooth substrate. Therefore, this laboratory investigation aimed to assess the impact of a hydrogen peroxide (HP)-free bleaching (HiSmile Methods: Sixty sound human premolar teeth were sectioned to produce dentin fragments and divided into two primary groups based on the bleaching agent used. Each group was subdivided into three subgroups (n = 10) per distinct bleaching regimens: (T Results: HP-based bleaching gel showed significant differences between measurement intervals in surface roughness, elastic modulus, and SBS parameters (P < 0.05). In contrast, HP-free bleaching gel showed insignificant differences within the group (P > 0.05). The SBS between dentin-composite was significantly affected with the use of HP-based bleaching gel, while HP-free bleaching gel showed insignificant difference between measurement intervals. The qualitative validation of the treatment's impact was further demonstrated using the scanning electron microscopy. Conclusion: The findings suggest that the bonding stability of composite restorations to dentin may be compromised after bleaching with an HP-based gel, whereas immediate bonding procedures can be safely conducted following the application of an HP-free bleaching gel.