Sodium hypochlorite solution penetration into human dentine: a histochemical evaluation

The aim of this study was 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.

Extracted maxillary central incisors were decoronated and their root canals were 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 min. A transverse section was obtained in the middle portion of the apical, middle and coronal thirds of each tooth. Under microscopic examination, irrigant penetration was evaluated by measuring the following: the bleached circumference of the root canal with respect to the stained circumference; bleached areas, mean and maximum penetration depth. For statistical analysis, Pearson's chi-squared test and one-way anova were used.

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 and 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 observed (P = 1).

No differences in penetration of irrigants with and without surfactants into dentinal tubules were observed in the middle and coronal thirds of incisor teeth.