An in vitro study on the efficacy of removing calcium hydroxide from curved root canal systems in root canal therapy

To compare the efficacy of various irrigants(citric acid, ethylenediaminetetraacetic acid（EDTA） and Na OCl) and techniques in removing Ca（OH）2 in two types of curved root canal systems, simulated root canals with specific curvatures were used to investigate the effects of different irrigants and instruments on Ca（OH）2 removal. The optimal methods were verified on extracted human teeth. Simulated root canals were assigned to one of two groups based on the irrigation solution: 10% citric acid or2.5% Na OCl. Each group was divided into four subgroups according to the technique used to remove Ca（OH）2 . The percentage of Ca（OH）2 removal in different sections of root canals was calculated. On the basis of the results obtained for the simulated canals, 10% citric acid and 17% EDTA were applied to remove Ca（OH）2 from the extracted human teeth with curved root canal systems. The teeth were scanned by micro computed tomography to calculate the percentage of Ca（OH）2 removal in the canals.In simulated root canals, we found that 10% citric acid removed more Ca（OH）2 than 2.5% NaOCl in the 0–1 mm group from the apex level（Po0.05）. Ultrasonic and Endo Activator activation significantly removed more Ca（OH）2 than a size 30 K file in the apical third（Po0.05）. However, there were no significant differences in any sections of the canals for 10% citric acid or 17%EDTA in removing Ca（OH）2 in extracted human teeth. We concluded that it was effective to remove residual Ca（OH）2 using the decalcifying solution with Endo Activator or Passive Ultrasonic Irrigation in a curved root canal system. A protocol for Ca（OH）2 removal was provided based on the conclusions of this study and the methods recommended in previous studies.