Root canal preparation can be regarded as the most important phase of the endodontic treatment. Its main purposes are to clean, disinfect, and shape root canals. These objectives, however, may be difficult to be attained in curved root canals or in teeth with complex internal anatomy. Residual bacteria and debris may remain unaffected in unprepared canal walls, isthmuses, lateral canals, apical ... [Show full abstract] ramifications, dentinal tubules, and recesses from oval/flattened canals and compromise the treatment outcome. Some strategies have been devised to improve the effects of chemomechanical procedures in teeth with root curvatures and complex anatomy.