Impacts of Contracted Endodontic Cavities on Primary Root Canal Curvature Parameters in Mandibular Molars.

•This study determined the effect of access design on canal curvature configuration.•A decreased angle of curvature occurred at each instrumentation stage for both accesses.•An increased radius of curvature was detected at each instrumentation stage for both accesses.•Instrumentation time was longer for CECs than TECs.•CECs in mandibular molars enabled instrumentation of curved type IV mesial canals.•CEC results for canal curvature configuration were comparable with TEC.