Abstract: ObjectiveTo evaluate the clinical effects of curved root canal preparation using M3-PRO.MethodsInclinical trial group, 70 curved root canals of permanent teeth were prepared using the instruments of M3-PRO (MP) and Protaper(PT) respectively(n =35).Standardized paralleling periapical radiographswere used to compare the curved root canal filling effect.The root canal preparation time,interappointment pain and instrument separation were compared. In vitro study,a total of 30 simulated root canals were divided into two groups. The pre-instrumentation and post -instrumentation images were recorded by microscope. The efficacy of the shaping ability of root preparation was analyzed.ResultsClinical trial group:The successful rate of canal filling: M3-PRO was 94.2% and the Protaper was 91.4%(P＞0.05). Thecanal preparation time: M3-PRO was （4.54±0.74）min and the Protaper was （6.68±1.10）min (P＜0.01). The rate ofinterappointment pain：M3-PRO was 5.7% and the Protaper was 8.5%(P＞0.05).No instrument separation appeared. In vitro study: The efficacy of the shaping ability of root preparation of M3-PRO was better than Protaper at 3, 4, 5,6mm away from apical.ConclusionM3-PRO can meet the clinical necessity for the curved root canals．

Key words: [Key words] curved root canals, M3-PRO, Protaper