RESUMO
To better assess the efficacy of mechanical preparation of root canals, transparent specimens of 250 extracted maxillary canines were investigated for canal configuration, thickness and curvature of the root canal, condition of any accessory canals, and location of the apical foramen. Fewer than 40% of the specimens showed accessory canals that were mechanically impossible to clean. The majority of the lateral branches were small, greater than a #15 file, and none of the branches were larger than a #20 file. Although apical foramina located away from the apex were observed in 30% of the maxillary teeth, 96% of all apical foramina were within 0.5 mm of the apex. Data on the thickness of the root and main canal in the apical portion and curvature of the root canal suggest that, for adequate apical preparation, a #60 file must be able to reach the apical constriction.