Abstract: Objective To evaluate the postoperative pain and the longterm clinical effect in treating the chronic apical periodontitis of the maxilla or the mandibule with the rotary NiTi instruments and the ultrasonic root canal irrigation which were applied jointly，independently or neither. Methods A total of 280 subjects with chronic apical periodontitis of maxilla and mandibule were selected and categorized into 4 groups randomly. The control group(n=69) was prepared by kfile and irrigated by injector. The NiTi group(n=70) was prepared by NiTi instruments and irrigated by injector. The ultrasonic irrigation group(n=70) was prepared by kfile and irrigated by ultraphonic. The union group(n=71) was prepared by NiTi instruments and irrigated by ultraphonic. All the groups were filled at once, and the postoperative pain reaction was evaluated after a week; after 2 years, the longterm clinical efficacy was assessed. Results After a week, the postoperative pain reaction of the control group was the most serious, whose incidence rate was 50.7%. The NiTi group and the ultrasonic irrigation group were slightly better, whose incidence rates were respectively 28.6% and 27.1%. The union group had the best result, the incidence rate of which was only 9.86%. After 2 years, there was no significant difference in the longterm clinical efficacy between any two groups（P>0.05）,besides the statistically significant difference between the control group and the union group（P<0.02）. Conclusion The treatment of the chronic apical periodontitis of the maxilla or the mandibule with the rotary NiTi instruments and the ultrasonic root canal irrigation jointly can reduce the incidence rate of the postoperative pain reaction, and can improve the longterm clinical efficacy, so it is wroth being promoted.

Key words: chronic apical periodontitis, clinical research, singlevisit root canal therapy, rotary nickeltitanium instruments, ultrasonic root canal irrigation