Abstract: Objective The aim of this study was to evaluate the incidence of pain after pulp canal therapy of pulp necrosis teeth using calcium hydroxide as an intracanal dressing. Methods Ninety single- root necrotic premolars of 90 patients participated in this study. These teeth were randomly divided into three groups of 30 teeth. The teeth in group A were treated in a single- visit approach, the teeth in group B with a two- visit approach without any intracanal dressing and the teeth in group C with a two- visit approach using calcium hydroxide as an
intracanal dressing. All of the patients were followed for 72 hours after treatment. The data were analyzed by chisquare test. Results There were significant difference between group A and group B, group B and group C（P<
0.05）. There was no significant difference between group A and group C（P>0.05）. Conclusion Calcium hydroxide can decrease painful responses to endodontic treatments