INTRODUCTION: Sodium hypochlorite (NaOCl) is the most commonly used root canal irrigant. The aim of this study was to evaluate the effect of concentration, time of exposure, and temperature on the penetration of NaOCl into dentinal tubules. METHODS: Thirty extracted human permanent maxillary anterior teeth with single canals were instrumented by using ProTaper rotary files. The teeth were then sectioned perpendicular to the long axis. The crowns and apical thirds of all the teeth were removed. The remaining roots were processed into 4-mm-long blocks and stained overnight in crystal violet. One hundred eight stained blocks were treated by 1%, 2%, 4%, and 6% NaOCl for 2, 5, and 20 minutes at 20 degrees C, 37 degrees C, and 45 degrees C, respectively. The depth of penetration of NaOCl was determined by bleaching of the stain and measured by light microscopy at magnifications of 20x and 40x. Statistical comparisons were made by using one-way analysis of variance, and Dunnett T3 tests were made for multiple comparisons. RESULTS: The shortest penetration (77 mum) was measured after incubation with 1% NaOCl for 2 minutes at room temperature. The highest penetration (300 mum) was obtained with 6% NaOCl for 20 minutes at 45 degrees C. After the initial penetration during the first 2 minutes, the depth of penetration doubled during the next 18 minutes of exposure. Temperature had a modest effect within each group on the depth of penetration and in most cases was not statistically significant (P > .05). Depth of penetration increased with increasing hypochlorite concentration, but the differences were small. Within each time group, depth of penetration with 1% NaOCl was about 50%-80% of the values with the 6% solution. CONCLUSIONS: Temperature, time, and concentration all contribute to the penetration of sodium hypochlorite into dentinal tubules.
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