Objectives: Considering the increasing use of vital bleaching procedures and the increased application of newly introduced resin-based materials for tooth restoration, this study was designed to evaluate the effect of 15% carbamide peroxide gel on the flexural strength of three resin-based restorative materials. Materials and Methods: Three different types of restorative materials namely Beautifil II giomer, Cention N, and Z250 micro-hybrid composite resin were evaluated in this in vitro, experimental study. Twenty-four bar-shaped specimens were prepared from each restorative material, totaling 72 specimens, and were randomly assigned to two subgroups with and without bleaching procedure (n=12). In the bleaching subgroups, 15% carbamide peroxide gel was applied on the specimen surface 8 h a day for 14 days. The flexural strength of the specimens was then measured. Two-way ANOVA was used to compare the flexural strength of the specimens. Results: There was a significant reduction in the flexural strength of materials following exposure to the bleaching agent (P<0.05). The flexural strength was significantly higher in the groups that did not undergo bleaching. However, the mean flexural strength of the restorative materials was not significantly different (P=0.12). Conclusion: The flexural strength of Beautifil II giomer, Cention N, and Z250 micro-hybrid composite resin could be compromised subsequent to bleaching with 15% carbamide peroxide gel. The three resin-based restorative materials exhibited similar flexural strength values irrespective of the use or no use of 15% carbamide peroxide gel.

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Background. The use of bleaching agents might result in microstructural changes in tooth structure andin restorative materials. This study compared the effects of bleaching with %15 carbamide peroxide and%35 hydrogen peroxide on the flexural strength of Cention N restorative material using the self-curedand dual-cured polymerization modes. Methods. Sixty bar-shaped samples of Cention N restorative material were included in this in vitrostudy and assigned to three groups (n=20) randomly: control, bleaching with %15 carbamide peroxideand bleaching with %35 hydrogen peroxide. Each group was divided into two subgroups: samplespolymerized in the self-cured mode and samples polymerized in the dual-cured mode. Then the flexuralstrengths of the samples were determined. Two-way ANOVA was used to compare flexural strengthsbetween the three groups in two polymerization modes, followed by post hoc Tukey test. Statisticalsignificance was defined at P<0.05. Results. The difference in the mean flexural strength was significant in terms of the bleaching regimen(P<0.001), with significantly lower flexural strength in the two bleaching groups compared to thecontrol group. However, the mean flexural strengths were not significantly different in terms of thepolymerization mode applied (P=0.14). Conclusion. The application of %15 carbamide peroxide and %35 hydrogen peroxide bleaching agentsdecreased the flexural strength of Cention N restorative material. Irrespective of the bleaching regimen,there was no significant difference in the flexural strength of Cention N between the self-curing anddual-curing polymerization modes.

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