Abstract: PURPOSE: To compare the effect of different root canal preparation methods on the incidence of interappointment emergencies (IAE) and root canal filling. METHODS: A total of 96 teeth requiring root canal therapy due to pulpitis or periapical periodontitis from August 2018 to August 2021 were selected. They were randomly divided into 2 groups: MT group was treated with Mtwo root canal preparation method modified by Mtwo machine nickel-titanium file, while synchronous group was treated with modified Mtwo preparation method and synchronous root canal length measurement. After root canal preparation, the trial point film was taken, calcium hydroxide was used to seal the root canal, and routine thermoplasticizied gutta-percha root canal filling was performed during the follow-up visit. SPSS 22.0 software package was used to analyze the incidence of IAE and filling effect after root canal therapy. RESULTS: There was no significant difference in the incidence of IAE between the two groups immediately after operation, three days and 1 week after operation(P>0.05); the incidence of IAE in synchronous group was significantly lower than that in MT group at 1 and 2 days after operation(P<0.05). The qualified rate of root canal filling in synchronous group was significantly higher than that in MT group (P<0.05). CONCLUSIONS: Synchronous method can reduce mechanical stimulation of apical area during root canal preparation, strictly control the working length of root canal and maintain apical barrier, thus reducing the incidence of IAE and effectively improving the qualification rate of root canal filling.

Key words: Machine niti system, Root canal instrumentation, Root canal length, Endodontic interappointment pain, Quality of root canal filling