An invitro evaluation of the effect of 10% Carbamide Peroxide on microleakage of two types of Microfilled and Hybrid Resin composites Dr. AR. Danesh Kazemi *- Dr. AR. Davari * - Dr. S. Maleki ** *Assistant Professor of Operative Dentistry Dept., Faculty of Dentistry, Yazd University of Medical Sciences. ** Dentist. Abstract Background and Aim: Composite resin restorations are widely used in dentistry. Therefore, it is important to identify possible causes of failures in this regard. The purpose of this study was to investigate the microleakage of two microfiled and hybrid resin composites following the use of 10% carbamide peroxide. Materials and Methods: In this experimental study, Class V cavities were prepared on the buccal surfaces of 150 human anterior teeth. These teeth were randomly divided into six groups and filled with two microfilled (D-E) and hybrid resin composites (B-C). The groups B and D were kept in contact with 10% carbamide peroxide for three weeks. Likewise, groups C and E were kept in contact with the same solution for four weeks. The specimens were rinsed and sectioned after being emmersed in 0.5% buffered fushin, and the microleakage was evaluated under stereomicroscope. Kruskal-Wallis and Mann-Whitney tests as well as Hotteling trace were used to determine the significant differences between the groups. Results: In comparison with the control group, composite microleakage was observed in all groups after emerging the samples in 10% carbamide peroxide. Microleakage was lower in the three-week group, when compared with the four-week one. However, the difference was statistically significant in the microfilled group. Conclusion: The microfilled composite restorations should be changed after using carbamide peroxide. Key words: Carbamide peroxide, Microleakage, Bleaching, Micro filled, Hybrid Correspondence Author: Operative Dentistry Dept., Faculty of Dentistry, Yazd University of Medical Sciences. e.mail: adaneshkazemi@yahoo.com | 
