Objective Curved canal preparation is much difficult in root canal therapy(RCT). Step back technique and rou- tine technique are still regularmethods in curved canal preparation. The purpose of this studywas to introduce a newmethod—re- verse flaring technique, and to investigate its preparation efficiency in intermediate-curvature canals.Methods 48 cases of lower first molars RCTwere collected, whichwere firsttreated because of pulpitis or apical periodontitis inWest China College of Stoma- tology, Sichuan University from Nov. 2001 to Aug. 2003, mesial canal curvature was intermediate (30°~60°), determined by Schineider method. Caseswere divided intotwo groups, in reverse flaringtechnique group, canal preparation in 27 caseswere fin- ished by reverse flaring technique, 21 cases by step back technique as control. In working length determination and fitting master cone stages, cases in two groupswhich fit full working lengthwere recorded, determined by radiogragh, and analyzed byχ2test. Results Inworking length determination stage, caseswhich fit full working length in reverse flaring technique groupwere signifi- cantly more than that of step back technique group (P
