evidence: ProTaper Next system maintained root canal curvature well and was safe to use either with path-finding files or alone.
intervention: group 1 with #10, #15 and #20 K-type (Dentsply Maillefer, Ballaigues, Switzerland) stainless steel manual files
comparator: group 3 with #16 ProGlider (Dentsply Maillefer) rotary instruments
outcome: performance of path-finding files