Dentinal tubule penetration of sodium hypochlorite and super-oxidized water using diode laser and passive ultrasonic activation: an in vitro confocal laser scanning microscopy study

BACKGROUND: Adequate irrigant penetration into dentinal tubules is essential for effective root canal disinfection, especially in anatomically complex areas of root canal system. Delivering irrigants into dentinal tubules, particularly in apical third, is frequently not possible with conventional needle irrigation. To improve irrigant penetration, irrigant activation methods such as passive ultrasonic and diode laser activation have been proposed. Super-oxidized water has shown potential as a less cytotoxic substitute irrigant for sodium hypochlorite; however, there is still little evidence on how well it penetrates dentinal tubules when used in conjunction with activation methods. This study used a diode laser and ultrasonic activation to assess and compare penetration of sodium hypochlorite and super-oxidized water into dentinal tubules. METHODS: Sixty extracted human single-rooted permanent teeth with closed apices were utilized in this in-vitro study. Based on type of irrigant (5.25% sodium hypochlorite or super-oxidized water) and activation method (conventional needle irrigation, passive ultrasonic activation or diode laser activation), specimens were randomly allocated into 6 groups. 0.1% Rhodamine-B dye was used to label irrigants. Teeth were sectioned at coronal, middle, and apical levels following standardized canal preparation and irrigation protocols. Dentinal tubule penetration was measured using confocal laser scanning microscopy. Two-way ANOVA and repeated-measures ANOVA followed by Bonferroni-adjusted post hoc analysis were used for statistical evaluation, with p < 0.05 considered statistically significant. RESULTS: Compared to conventional needle irrigation, activated irrigation resulted in significantly increased dentinal tubule penetration. Across all canal levels, diode laser activation showed the highest penetration, followed by passive ultrasonic activation. Conventional irrigation showed the lowest penetration. Penetration decreased from coronal to apical third in every group. Super-oxidized water demonstrated dentinal tubule penetration similar to sodium hypochlorite when used in conjunction with activation procedures; under activated conditions, there was no statistically significant difference between two irrigants. CONCLUSIONS: Regardless of irrigant utilized, irrigant activation is essential for enhancing dentinal tubule penetration. The most successful method was diode laser activation, which was followed by passive ultrasonic activation. Super-oxidized water showed penetration comparable to sodium hypochlorite when activated, suggesting its potential for further investigation as an alternative irrigant under activated irrigation conditions.