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SUMMARYThis in vitro study assessed the fracture resistance of endodontically-treated teeth undergoing combination bleaching with 38% and 9.5% hydrogen peroxide gels as in-office and at-home bleaching techniques, respectively. In addition, the effect of an antioxidizing agent, sodium ascorbate, was investigated.Methods and Materials: Sixty maxillary premolars were endodontically-treated, received a glass ionomer barrier as a mechanical seal and were embedded in acrylic resin up to the cemento-enamel junction. The specimens were divided into four groups (n=15) as follows: G I: no bleaching, access cavity restored with resin composite (negative control); G II: bleached for three weeks daily using 9.5% hydrogen peroxide for two hours and three sessions of in-office bleaching using 38% hydrogen peroxide every seven days, then restored (positive control); G III: bleached similar to G II and restored after one week; G IV: bleached similar to G II, along with the use of an antioxidizing agent for 24 hours, then restored. In each in-office and athome bleaching session, the whitening gels were applied to the buccal surface of the tooth and placed inside the pulp chamber (inside/outside bleaching technique). Finally, the specimens underwent fracture resistance testing; the data were analyzed using ANOVA and Scheffé's test (α α=0.05). M Khoroushi • A Feiz • R Khodamoradi Clinical RelevanceThe fracture resistance of endodontically-treated teeth decreases after combination bleaching. The use of sodium ascorbate as an antioxidizing agent reverses decreased fracture resistance. In addition, it decreases the treatment period and the risk of catastrophic crown fractures.

For bleaching AH26 sealer-stained teeth, carbamide peroxide gel and carbamide peroxide gel mixed with sodium perborate were equally effective and significantly better than sodium perborate mixed with water.

The aim of the study was to determine and compare the reaction of rat subcutaneous connective tissue to resin composites polymerized with different lights curing and lightening methods. In this in vivo study, 20 mature Wister Albino rats were used. The composite discs, 4 mm in diameter and 2 mm thick, were cured by QTH or LED light curing units with 4 different lightning methods (full power QTH, full power LED, pulse LED, and ramp LED). Five resin composite discs were implanted in each rat, so that 4 of 5 discs for implantation of cured composite discs differently and central one as control without implantation. After sacrificing at 7, 14, 30, and 60 days the inflammatory grade, fibrosis, and necrosis were determined. Freedman and Cochran tests were used to analyze the data using SPSS software ver. 15. The results of the study showed significant differences in inflammation grade and fibrosis among control group and 4 experimental groups at day 14 (P < 0.05). In necrosis, there was no significant difference among 4 groups in different times (P > 0.05). In conclusion, neither the type of light curing units (LED or QTH) nor the lightening methods can affect the grade of inflammatory reaction.

Objectives:Calcium hypochlorite (Ca(OCl)2) is currently used as a root canal irrigant. The aim of this study was to compare the effects of calcium hypochlorite and sodium hypochlorite (NaOCl), as root canal irrigants, on the bond strength of posts cemented with a self-adhesive resin cement.Materials and Methods:In this in-vitro study, 40 maxillary central incisors with similar root lengths were decoronated. The teeth were randomly divided into five groups based on the irrigant used: Group 1: normal saline (control), Group 2: 2.5% sodium hypochlorite, Group 3: 5.25% sodium hypochlorite, Group 4: 2.5% calcium hypochlorite, and Group 5: 5% calcium hypochlorite. Root canal treatments were performed with Gates-Glidden drills and the irrigant corresponding to each group was used upon changing the file and for irrigating the post space. Then, glass fiber posts were cemented by BisCem self-adhesive cement. After applying 1,000 thermocycles at 5–55°C, three samples of the mid-section of each root were prepared: one for scanning electron microscopy (SEM), and the rest for push-out testing. Data were analyzed with SPSS 23 software using one-way analysis of variance and post-hoc Tukey’s test.Results:The highest and lowest mean bond strengths were recorded in groups 5 and 1, respectively. There was a significant difference between the 5% calcium hypochlorite group and the other groups (P<0.001). The difference between the other groups was not significant.Conclusion:The use of 5% calcium hypochlorite with self-adhesive cements increases the push-out bond strength of fiber posts to radicular dentin.