Root canal system of the mandibular incisor.

To better assess the efficiency of the mechanical preparation of root canals, 1085 transparent specimens of extracted mandibular incisors were examined for canal configuration, thickness and curvature of the root canals, condition of any accessory canals, and location of the apical foramen. Greater than 85% of the root canals possessed a single canal (Type I). Of specimens in which furcation was observed, only 3% possessed two separate canals (Type III and IV). Fewer than 30% of the specimens showed accessory canals that were mechanically impossible to clean. The majority of the lateral branches were small, greater than 80% of the specimens were smaller than a #15 reamer, and none of the branches were larger than a #30 reamer. Although apical foramina located distal to the apex were observed in about 50% of the specimens, 83.6% of all apical foramina were within 0.5 mm of the apex, and 99.5% were within 1.0 mm. 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 #40 reamer must be able to reach the apical constriction.