Heated distilled water with or without continuous ultrasonic irrigation improves final irrigation efficacy and reduces dentine erosion

Objectives: The present study evaluated the effects of using heated distilled water (HDW), with or without continuous ultrasonic irrigation (CUI), on smear layer removal and deterioration of root dentine microstructure. Materials and Methods: After chemomechanical preparation, 60 human teeth were longitudinally cleaved into two halves for smear layer quantification at the cervical-third, middle-third and apical root-third of the canal space. After reassembly, the root canals were irrigated with 17 % EDTA, followed by one of the six final irrigation protocols (n = 10) - G1: conventional irrigation (CI)+NaOCl at 25 °C; G2: NaOCl at 25 °C + CUI; G3: CI with DW at 25 °C; G4: DW at 25 °C + CUI; G5: CI + HDW at 65 °C; G6: HDW at 65 °C + CUI. Tooth-halves were processed and examined by scanning electron microscopy. The percentage of opened dentinal tubules in the irrigated areas of the canal space was expressed as a percentage of the total surface area. Dentine erosion was classified by numeric scores. Smear layer removal was analysed with ANOVA and Student-Newman-Keuls tests; dentine erosion was analysed with Cohran-Mantel-Haenstel statistic (α = 0.05). Results: The cervical-third had a higher percentage of open dentinal tubules for all groups (p < 0.05). In G2, the middle-third had a lower percentage of open tubules, which was significantly different from the other groups (p < 0.05). Groups that utilised NaOCl as the final irrigant had more extensive erosion when CUI was used. Conclusion: Heated distilled water, with or without CUI, was as efficient as 1 % NaOCl in the final cleaning of the instrumented canal space. The use of HDW produces less extensive dentine erosion. Clinical significance: Heated distilled water removes smear layers with less deleterious effects on dentine microstructure and may be considered a final irrigant after mechanical preparation and EDTA chelation.