Abstract: Objective Comparison the effect of four root cancal disinfectants alleviating clinical symptoms of periapical periodontitis primary molar teeth. Methods To divide 160 primary molar tooth having apical periodontitis randomly into four groups. All the tooth opened and prepared conventionally and then ultrasonic irrigation. Antibiotic paste was given in group A, vitapex paste was given in group B,calcium hydroxide paste in group C and cotton ball of camphor phend in group D for root canal disinfection．The effects was observed ten days after medication placement．Results The cure rate of abscess after 10 days is significant difference between antibiotic paste and other three groups(P=0.005),vitapex paste and calcium hydroxide are similarity (P=0.284),but camphor phend showed poor effect (P=0.026)．Antibiotic paste is similar with camphor phend(P=0.499)in incidence of postoperation pain within 24 hours,but better than vitapex paste(P=0.014）and calcium hydroxide(P=0.045). There are no significant difference between all the groups in percussion pain(P=0.417)．Conclusion Antibiotic paste could alleviate clinical symptoms of periapical periodontitis primary molar teeth effectively.

Key words: primary molar teeth, periapical periodontitis, calcium hydroxide, antibiotic paste