Objective: Teeth bleaching causes an immediate decrease in resin composite bonding ability. This study aimed to investigate the influence of various antioxidants on resin composite bond strength to bleached enamel. Materials and methods: One hundred and ten human maxillary incisors were used. A negative control (group A) (n = 10) was assigned (no bleaching-no antioxidant). The remaining teeth were divided into two groups (n = 50) according to the bleaching agent used: group B (40% hydrogen peroxide) and group C (35% carbamide peroxide). Both groups were subdivided into five subgroups (n = 10). A positive control subgroup (no antioxidant) and other four subgroups according to the antioxidant solution used (10% sodium ascorbate, 10% grape seed extract, 10% green tea extract, and 5% alpha-lipoic acid). After resin composite building, the micro-shear bond strength test was performed. Fracture analysis was examined using a stereomicroscope. Statistical analysis was performed using a two-way analysis of variance and Tukey's HSD post hoc test. Results: Bond strength significantly decreased after bleaching and there was no significant difference between bleaching agents (P < .0848). Except for alpha-lipoic acid subgroups, the other antioxidants subgroups revealed significantly higher bond strengths than bleached control subgroups (P < .0001). Conclusion: All antioxidants used except alpha-lipoic acid were effective in the reversal of compromised bonding after bleaching. Clinical significance: Immediate bonding procedures after bleaching are requisite when bleaching fails to treat teeth discoloration and the direct composite veneer is considered, also when shades of old composite restorations become mismatched after bleaching and should be replaced. Immediate reestablishment of resin bond strengths after bleaching can be achieved by using several antioxidants without the need for delay.

Objective: To evaluate fluoride release and uptake behaviors of the new bioactive resin modified glass ionomer cement (RMGIC) (activa bioactive glass ionomer) compared to conventional glass ionomer cement(CGIC) (Fuji IX GP).Material and Methods: Forty specimens were prepared (10 mm x 2 mm) from Fuji IX GP glass ionomer and Activa Bioactive RMGI according to manufacturer's instructions. The specimens stored in deionized water and fluoride release were assessed daily in the first week then weekly till the third week using ion chromatography. The specimens of each material were divided into two equal subgroups according to the recharging agents used ; either0.05% mouth wash (226 ppm sodium fluoride, G.U.M, Sunstar, Germany, GmbH) or 5% sodium fluoride varnish (22.600ppm fluoride, enamel pro varnish Premier Dental, Plymouth Meeting, PA,19462,USA). Fluoride release after recharge was measured and recorded daily for a total of 5 days. Data were analyzed by Two way ANOVA and Duncans test (α = 0.05) using the SPSS software program.Results: CGIC release higher amount of fluoride than RMGIC. Professionally applied fluoride varnish showed better recharging ability than home care fluoride mouth wash and CGIC had greater recharge ability than new RMGIC.

Objective: To evaluate the influence of fluoride varnish and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on bleached enamel microhardness. Materials and Methods: Thirty human permanent incisors were selected to preparer thirty enamel specimens. All specimens were bleached using 40% hydrogen peroxide bleaching agent (power whiting YF). The bleached enamel samples were divided into three equal groups (n = 10) according to the used remineralizing agent. Group A was treated by CPP-ACP past (GC Tooth mousse), group B was treated by Fl varnish (Biflourid 10) and group C was stored in artificial saliva. The microhardness was assessed using Vicker test (before bleaching, after bleaching and after application of different remineralizing agents). The data was collected and statistically analyze using two-way ANOVA and post hock LSD test at (P< 0.05). Results: Enamel microhardness has diminished significantly in all groups after bleaching. After application of remineralizing agents, there was a significant increase in microhardness. There was no significant difference between groups A and B, while there was significant difference between these groups and group C. Conclusions: Using fluoride, CPP-ACP or artificial saliva improves bleached enamel microhardness.

Objective: To examine the influence of different universal adhesives on fracture resistance of endodontically restored teeth.Materials and Methods: Fifty sound maxillary premolars were collected. MOD cavity and root canal treatment were performed in 40 teeth only. The width of the cavity was one-third of the inter-cuspal distance at the occlusal portion and one-third of the bucco-lingual width of proximal boxes. The floor of the cavity was coronally prepared by 1 mm to the CEJ. The cavo-surface margins were prepared at a butt joint. All samples were assorted into five equal groups (N=10): group I: intact teeth (+ve control), group II: prepared unrestored (-ve control), groups III, IV, and V: these groups had root canal treatment and standardized MOD cavities then restored with final resin composite restorations (Filtek Z350 XT) by using three types of adhesive systems; Single Bond Universal, All-Bond Universal and Tetric N-Bond Universal, respectively. The teeth were mounted to universal testing machine and subjected to compressive load at crosshead speed 0.5 mm/min. Fracture modes were evaluated under a stereomicroscope at magnification of 12X. Statistical analysis was performed using SPSS, version 20.0.Results: There was significant improvement in fracture resistance in restored teeth (group III, IV and V) than unrestored teeth (group II), but didn't reach the fracture resistance of sound teeth (group I). There was no significant difference between restored groups. Conclusions:According to the limitations of this study, resin composite restoration of endodontically treated teeth using different universal adhesives improve fracture resistance of these teeth.

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