Histochemical evaluation of activated sodium hypochlorite into human dentin

Aim: The aim of this study was to evaluate ex vivo the penetration depth of sodium hypochlorite in human dentin, with manual and ultrasonic activation, using a histochemical staining technique under vacuum and the bleaching ability of NaOCl. Methods: The root canals of 36 extracted single canal teeth were shaped to a size 30. .07 taper. Dentinal tubules were stained with 8% copper sulphate solution and 5% ammonium hydroxide followed by a 1% rubeanic acid alcohol solution under vacuum. The samples were irrigated for 1 min with 5mL of 5.25% sodium hypochlorite solution, then the irrigant was activated for 1 minute by Manual Dynamic Agitation (MAD) with K-file (Kerr, Italy) or Passive Ultrasonic Activation (PUI) with Irrisafe insert (Satelec Acteon group, Merignac, France), according to the corresponding treatment group. A cross-section was obtained in the central portion of each root third. Under microscopic examination, sodium hypochlorite penetration into dentin was evaluated by measuring the following parameters: 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. Results: Only 58% of the apical sections showed stained dentinal tubules; therefore, these were excluded from further comparisons. The percentage of copper sulphate-stained circumference of the root canals increased from the middle to coronal level in both groups, with a statistically significant difference (P<0.001). In the middle and coronal third, the average root canal bleached circumference was 98-100% of the stained circumference, with no difference within and between groups, and the bleached area was 125490-298290 μm², respectively. The bleached circumference values (also those related to root canal) and bleaching areas of the coronal third were significantly higher than those recorded in the middle third in each group, while no differences between groups at the same level were observed. The mean penetration depth ranged from 63 to 69 μm and the maximum was from 96 to 106 μm, without inter- and intra-group differences (P = 1). Conclusion: No differences in dentinal tubules penetration of 5.25% sodium hypochlorite solution were observed with manual and ultrasonic activation in the middle and coronal root thirds of single canal teeth.