In adults, paranasal sinus agenesis is an uncommon anomaly that appears mainly in the frontal sinus. The aim of this study was to investigate the prevalence of agenesis of the frontal sinus using computed tomography in a population of Iranian individuals. Computed tomographic scans in the axial and coronal planes of the frontal sinus of 565 patients were examined for evidence of the absence of the frontal sinus. A bilateral agenesis of the frontal sinus was seen in 8.32% of cases, and unilateral absence of the frontal sinus was observed in 5.66%. The information provided in the current study is useful for some craniofacial surgeries and improves the anthropometric knowledge of humanity. There are limited studies on agenesis of the frontal sinus in the literature, but comparing our findings with the available data, there were differences regarding the incidence of this condition. This may be related to geographic and racial features. More studies on other population are required.

Objective:The aim of this study was to comparatively investigate the neutralizing effect of antioxidant treatment and delayed bonding after bleaching with hydrogen peroxide on the shear bond strength of a composite resin (CR) and resin-modified glass ionomer (RmGI) to enamel.Materials and Methods:Ninety-six freshly extracted human 3rd molars with flat enamel surfaces were divided into six experimental groups (n=12/group) and two control groups (n=12/group). After initial preparation, specimens in Groups 1 and 5 (control groups) were not bleached and the buccal enamel surface of specimens were bonded immediately with CR and RmGI. The samples of the remaining groups were all bleached six hours a day for seven days consecutively. Immediately after bleaching, groups two and six specimens were bonded with CR and RmGI. Groups 3 and 7 specimens were immersed in distilled water at 37°C for 7 days and the specimens in Groups 4 and 8 were treated with 10% sodium ascorbate as an antioxidant agent after bleaching. Specimens in Groups 3 and 4 were bonded with CR and Groups 7 and 8 specimens were bonded with RmGI immediately. After specimens were bonded, the shear bond strength (SBS) was measured. The SBS data analyses were subjected to one-way analysis of variance (ANOVA) followed by Tukey test for comparison of specific mean values.Results:The mean SBS value in Group 2 (immediately bonded with CR after bleaching) was significantly lower than other CR groups (P=0.045). RmGI did not bond to buccal enamel surface of specimens in group 6. There was no significant difference between other groups bonded with RmGI (P>0.05).Conclusions:Applying 10% sodium ascorbate hydrogel and one week delay before bonding resulted in reversal of reduced bond strength of CR and RmGI to bleached enamel.

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