Influence of dental bleaching on the microhardness and flexural strength of resin composites

Purpose. This study aimed to examine the influence of dental bleaching systems (home bleaching system and two in-office bleaching systems) on the surface microhardness, and flexural strength of the two resin composite restorative materials (Beautifil II and OliREVO). Methods. For each test, a total of 48 samples were prepared with both types of composites. The samples of each type of composite were divided at random into four groups each of six samples, control group (C) was not bleached and kept in distilled water, other three groups (G1, G2, and G3) were bleached with 10% hydrogen peroxide (HP) home beaching, 35% and 40% HP in-office bleaching systems, respectively. To measure the composite resin's microhardness, a Vickers microhardness tester was used, while a universal testing machine was used to measure its flexural strength. Results. For statistical analysis, Duncan and ANOVA tests were used. A p-value ≤0.01 indicates statistically significant results. In-office bleaching systems (35% and 40% HP) significantly reduced microhardness and flexural strength of the used resin composites. Generally, the hardness and flexural strength of Beautifil II were better than OliREVO composite. Conclusion. Regarding the physical properties of composite resins, the microhardness and flexural strength may be compromised by bleaching treatments.