RESUMEN
Bleaching teeth can lead to decreased calcium, phosphate and fluoride content of enamel which may cause decreased enamel micro-hardness. Reportedly, the topical use of fluoride can help regaining those minerals. The aim of this study was to evaluate the effect of fluoride therapy on enamel micro-hardness when used before or after bleaching. Total of 60 premolar teeth were divided into 5 groups. The occlusal surface in all teeth were flattened and covered with nail varnish. Initially, all specimens were inserted in artificial saliva for 7 days. Group 1 used as negative control. Samples in group 2 were bleached 2 times with 30 minutes interval for 5 days, using 45% carbamid peroxide. Group 3 samples were exposed to fluoride varnish for 5 minutes. Group 4 exposed to fluoride varnish for 5 minutes, bleached 2 times for 30 minutes in 5 day intervals. Group 5 samples were treated same as group 4, however, followed by fluoride varnish for 5 minutes. Micro hardness for each group measured in 3 points after cleaning the occlusal section. The LSD and ANOVA tests were used for data analysis. This study showed, reduction in enamel surface hardness can be compensated by fluoride application. Group 2 [bleached only] showed the minimum micro hardness [294.38], and group 3 [exposed to fluoride only] showed the maximum micro hardness [455.36]. Fluoride therapy can affect enamel micro-hardness before and after bleaching. The application of fluoride varnish is recommended after exposing teeth to bleaching agents