Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 17 0 2020 11 09 3411 3411 Soodabeh Kimyai Dental and Periodontal Research Center, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran AND Department of Operative Dentistry, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran Yasaman Ghavami Lahij Department of Operative Dentistry, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran Mehdi Daneshpooy Department of Operative Dentistry, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran Elmira Jafari Navimipour Department of Operative Dentistry, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran Parnian Alizadeh Oskoee Department of Operative Dentistry, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran 2020 01 05 2020 07 04 Objectives: Considering the ever-increase use of vital bleaching procedures and an increase in the use of newly introduced resin-based materials for the restoration of teeth, this in vitro study was designed to evaluate the effect of 15% carbamide gel on the flexural strength of three resin-based restorative materials. Materials and Methods: Three different types of restorative materials, Beautifil II giomer, Cention N and Z250 micro-hybrid composite resin, were evaluated in the current study. Twenty-four bar-shaped samples were prepared from each restorative material, totaling 72 samples, and randomly assigned to two groups: with and without bleaching procedures (n=12). In the groups with a bleaching procedure, 15% carbamide peroxide gel was applied 8 hours a day for 14 days. The flexural strengths of the samples were determined. Two-way ANOVA and post hoc Tukey test were applied to compare the flexural strengths of the samples. Results: There were significant differences in the flexural strengths of the materials in terms of the exposure to the bleaching agent (P<0.05), with significantly higher flexural strength in the groups without a bleaching procedure. However, the mean flexural strengths were not significantly different in terms of the restorative material (P=0.12). Conclusion: It was concluded that 15% carbamide peroxide bleaching gel significantly decreased the flexural strengths of Beautifil II giomer, Cention N and Z250 micro-hybrid composite resin. There were no significant differences in the mean flexural strengths between the three resin-based restorative materials, irrespective of the use or no use of 15% carbamide peroxide gel. https://fid.tums.ac.ir/index.php/fid/article/view/3411 https://fid.tums.ac.ir/index.php/fid/article/download/3411/1822