ABSTRACT
Objective@# To compare the efficiency of four methods that remove calcium hydroxide in root canals and to guide clinical practice. @* Methods @# Sixty-five isolated mandibular single root canal premolars were collected. After crown cutting and root canal preparation, a tooth was randomly selected as the blank control group, and the remaining 64 teeth were equally divided into Groups A and B (n = 32). Group A was injected with water-soluble calcium hydroxide, and Group B was injected with oil-soluble calcium hydroxide. After 2 weeks of drug sealing, Groups A and B were randomly divided into 4 groups (n = 8), including the lateral opening syringe group, sonic vibration group, ultrasonic group, and Er: YAG laser group. Before and after calcium hydroxide removal, the samples were scanned by cone-beam CT, and the data were imported into Mimics for 3D reconstruction. The root canal was divided into the following segments: superior root segment, middle and apical, and the calcium hydroxide volume of each segment of the root canal was calculated. The volumes of calcium hydroxide before and after removal were V1 and V2, respectively, with a clearance rate = (V1-V2)/V1×100%. Three-factor ANOVA was used for statistical analysis. After Groups A and B were reconstructed, the apical region with residual calcium hydroxide was selected, and the blank control was observed by scanning electron microscopy (SEM). @*Results @# Two types of calcium hydroxide could not be completely removed by the four flushing methods. The clearance rate of water-soluble calcium hydroxide was higher than that of oil-soluble calcium hydroxide (P<0.001). Among the three segments of the root canal, the clearance rate of the apical segment was lower (P<0.05). The Er: YAG laser treatment group showed the highest removal efficiency of two kinds of calcium hydroxide, which was higher than that of the other groups, especially in apical of the root. Compared with the sonic wave washing group and the syringe washing group, the ultrasonic wave washing group exhibited significant advantages (P<0.05). The clearance rate of the sonic wave washing group was higher in the oily calcium hydroxide root middle group than in the syringe washing group (P<0.05). SEM showed that the two kinds of calcium hydroxide could not be completely removed, but the residual rate of oil-soluble calcium hydroxide was large.@*Conclusion @# Both types of calcium hydroxide could not be completely removed, and compared to water-soluble calcium hydroxide, oil-soluble calcium hydroxide was more difficult to remove. Among the four cleaning methods, Er:YAG laser swing washing showed the higher cleaning efficiency.