A Cone-beam Computed Tomographic Study of Apical Surgery-related Morphological Characteristics of the Distolingual Root in 3-rooted Mandibular First Molars in a Chinese Population

A new classification was proposed for DL roots in 3-rooted mandibular first molars based on the root canal curvature. Type I is unsuitable for apical surgery. Access to the type II DL root apex should be through the DB root apex, whereas access to the type III DL root apex through the MB root apex is more feasible. Apical surgery on types II and III DL roots may be accomplished when the depth of the root-end preparation is reasonably reduced, and fine and personalized angulated ultrasonic retro tips are used.