Objective    To investigate the correlation of diabetes mellitus (DM) and endodontic interappointment pain (EIP) in root canal therapy (RCT).       Methods    Seventy-nine DM patients and 82 patients without DM were recruited

86 teeth required RCT in each group. DM patients were subdivided into two groups by the level of fasting plasma glucose (FPG): poorly controlled group if FPG9.0 mmol/L

and well controlled group if FPG7.8 mmol/L. The correlation of EIP incidence rate

algesic degree and algesic time after RCT was statistically analyzed.      Results    The EIP incidence rate and the incidence at given time in poorly controlled group were higher than well contolled and non-DM groups (P0.05). The algesic severity of poorly controlled group was more than well controlled and non-DM groups (P0.05). No statistic differences were between well controlled and non-DM groups (P0.05). However

in each group

the incidence rate of different algesic severity decreased with the increasing algesic severity.      Conclusion    EIP will occur in DM patients within a week after RCT. Well controlling of the blood glucose can reduce the incidence rate of EIP.