2009; Vol. 6, No. 2 78 Original Article Effect of Two Forms of Sodium Ascorbate on Microleakage of Composite Restorations Immediately after Bleaching S. Kimyai 1 ~ , S. Rahimi 2 , M. Lotfi 2 , H. Valizadeh 3 , N. Mohammadi 4 , E. Jafari Zareh 5 1 Associate Professor, Department of Operative Dentistry, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran 2 Associate Professor, Department of Endodontics, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran 3 Associate Professor, Department of Pharmaceutics, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran 4 Assistant Professor, Department of Operative Dentistry, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran 5 Dentist, Private Practice ~ Corresponding author: S. Kimyai, Department of Opera- tive Dentistry, Faculty of Den- tistry, Tabriz University of Medical Sciences, Tabriz, Iran. kimyais@tbzmed.ac.ir Received: 7 May 2008 Accepted: 22 October 2008 Abstract: Objective: The present in vitro study was undertaken to compare the effects of hydrogel and solution forms of sodium ascorbate on microleakage of composite restorations subse- quent to a non-vital bleaching procedure with 10% carbamide peroxide. Materials and Methods: Forty-eight sound extracted human maxillary incisors were ob- tained. Following root canal therapy, the teeth were randomly divided into an unbleached control group (group 1) and three experimental groups in which bleaching was performed (12 teeth in each group). Non-vital bleaching with 10% carbamide peroxide was carried out for periods of 8 hours a day for one week. In group 2, the specimens were restored immediately after bleaching. Group 3 specimens were treated with sodium ascorbate solu- tion, whereas in group 4 specimens, sodium ascorbate hydrogel was used before place- ment of composite restorations. Following thermocycling, the specimens were subjected to dye leakage (methylene blue) test. Statistical analysis was carried out using Kruskal- Wallis and Dunn multiple comparison tests at a significance level of P<0.05. Results: Significant differences existed in microleakage scores among the four groups (P<0.0005). Pairwise comparison of groups with Dunn test revealed that higher micro- leakage scores in group 2 compared to each of the other three groups was statistically sig- nificant (P<0.001) while the differences between other groups were not statistically sig- nificant (P>0.05). Conclusion: Ten percent carbamide peroxide significantly increases microleakage of composite restorations when bonding is performed immediately following non-vital bleaching. Compromised sealing ability of composite restorations is reversed with applica- tion of both forms (hydrogel and solution) of sodium ascorbate, as an anti-oxidant. Key Words: Tooth Bleaching; Composite Resins; Dental Leakage; Hydrogel; Ascorbic Acid; Marginal Adaptation (Dentistry) Journal of Dentistry, Tehran University of Medical Sciences, Tehran, Iran (2009; Vol. 6, No.2) INTRODUCTION Ten percent of teeth undergoing root canal therapy show tooth discoloration, which re- sults in aesthetic problems [1]. Non-vital bleaching is used successfully for whitening of root-filled teeth [2]. One of the non-vital bleaching methods is walking technique using 10% carbamide peroxide [3]. However, previ- ous studies have shown that bleaching agents adversely affect the bond strength and sealing ability of composite restorations when bonding procedure is performed immediately after