Abstract: Objective: To compare the efficacy of five techniques on removal of calcium hydroxide in curved canals. Methods: Fifty simulated resin canals with 45°curvature were prepared and randomly divided into 5 groups (n=10). Calcium hydroxide was injected into the root canals, and then the samples were scanned by cone beam CT to evaluate the volume of calcium hydroxide. Five techniques including needle irrigation, PIPS laser-activated irrigation, ultrasonic irrigation, sonic irrigation, and XP-endo finisher file were used to remove the calcium hydroxide. After cone beam CT scanning, the volume of the residual calcium hydroxide and the reduction rate of calcium hydroxide were calculated. The data were analyzed using Kruskal-Wallis H test at the significance level of P＜0.05. Results: The residual calcium hydroxide volume was 0mm3 (0mm³, 0.08mm³) in the PIPS laser-activated irrigation group, which was lower than those of other groups (P＜0.05). The reduction rate of calcium hydroxide was 100.00% (98.89%, 100.00%) in the PIPS laser-activated irrigation group, which was higher than those of other groups (P＜0.05). Reduction rate in the ultrasonic irrigation group and XP-endo finisher group were higher than that of sonic irrigation group (P＜0.05). Conclusions: None of five techniques could completely remove the calcium hydroxide from the curved root canals. Compared with other four techniques, PIPS laser-activated irrigation was significantly more effective in the removal of calcium hydroxide in the curved canals.

Key words: Calcium hydroxide, Laser-activated irrigation, Cone beam-CT, Root canal irrigation, Curved canals