Sodium hypochlorite solution penetration into human dentine: a histochemical evaluation

Aim To evaluate ex vivo the penetration depth of sodium hypochlorite solutions, with and without surfactants, into human dentine using a histochemical stain and the bleaching ability of NaOCl. Methodology Extracted maxillary central incisors were decoronated and their root canals shaped to a size 30, .07 taper. Dentinal tubules were stained with 10% copper sulphate solution followed by a 1% rubeanic acid alcohol solution under vacuum. Specimens were irrigated with 5 mL of Niclor 5 (5.25% NaOCl solution) or 5 mL of Hypoclean (5.25% NaOCl solution + surfactants) according to the corresponding treatment group, for 2 minutes. A transverse section was obtained in the middle portion of the apical, middle and coronal third of each tooth. Under microscopic examination irrigant penetration was evaluated by measuring: the bleached circumference of the root canal with respect to the stained circumference; bleached areas, mean and maximum penetration depth. For statistical analysis, Pearson Chi-squared test and one-way ANOVA were used. Results Only 30% of dentine tubules in the apical portions were stained, therefore these were excluded from further comparisons. In the middle and coronal thirds the average bleached circumference of the root canal was 80-99% of the stained circumference, the bleached area was 73757 - 135107 μm2. The average penetration depth ranged from 39 to 62 μm and maximum penetration from 74 to 131 μm. For all reported results no differences within and between groups were found (P = 1). Conclusion No differences in penetration of irrigants with and without surfactants into dentinal tubules were found in middle and coronal third of incisor teeth.