Abstract: Objective · To evaluate the clinical application effect of two nickel-titanium engine driven systems on moderate curved root canals. Methods · Ninety mesial root canals with moderate curvature of extracted human first mandibular permanent molar were randomly divided into three groups: M3 PRO Group, MTwo group and K group. The glide path was firstly preparedusing 10/04 file in M3 PRO group and MTwo group and 10 file in K group respectively .Then the preparation of root canals up to 25 was performed according to the instruction manual in each different group using standardized technique. All data including time required in glide path preparation, shaping preparation, total root canals preparation and changes of working length in root canal were recorded and analyzed statisticallyusing Analysis of Variance (ANOVA) and LSD-t tests (PResults · Root canal glide path preparation time: MTwo group showed significantly less preparation time while M3 PRO group exhibited significantly the longest preparation time. There was significant difference between MTwo group and M3 PRO group (P0.001). Root canal shaping preparation time: M3 PRO group showed significantly less preparation time while K group exhibited significantly the longest preparation time. Both MTwo group and M3 PRO group showed significantly less preparation time than K group (P0.004, P0.001), but there was no significant difference between MTwo group and M3 PRO group (P0.573). Total root canal preparation time: MTwo group showed the shortest time while K group exhibited the longest time. There were significant differences between MTwo group, M3 PRO group and K group （P0.004, P0.033), but no significant difference between MTwo group and M3 PRO group (P0.451). Changes of root canal working length: There were significant differences among the three groups (P0.037, P0.037, P0.000). M3 PRO group showed a minimal change while K group exhibited significant changes. Conclusion · MTwo nickel-titanium engine driven system with 10/04 file preform a high efficiency in glide path preparation, whilst M3 PRO nickel-titanium engine driven system show less changes in working length. Under the circumstancesthe total time required for root canal preparation is not significant, M3 PRO nickel-titanium engine driven system is more suifor root canal preparation in moderate curved root canals.

Key words: nickel-titanium engine driven system, moderate curved root canals, permanent molar, glide path, root canal shaping ability