Usually, teeth with single roots present single canals as in mandibular and maxillary anterior teeth. However, particular tooth types, such as mandibular premolars and incisors, are recognized as exhibiting a distinct range of variations in the morphology of their root canal system. In mandibular incisors, often a dentinal bridge is present in the pulp chamber dividing the root into two canals. The two canals usually join and exit through a single apical foramen, but they may persist as two separate canals. On occasion one canal branches into two canals, which subsequently rejoin into a single canal before reaching the apex. The incidence of two canals in mandibular incisors has been reported to be as low as 0.3% and as high as 45.3%. The wide range of variation reported in the literature regarding the prevalence of a second canal in mandibular incisors has been mostly related to methodological and racial differences.
(Very soon on the Journal of Endodontics)