An evaluation of canal morphology at different levels of root resection in mandibular incisors.

One hundred randomly selected mandibular incisors were examined to assess the prevalence and location of two canals and to describe the canal anatomy that may be encountered during apical surgery. Sections of the root were cut at 1, 2, and 3 mm from the apex, simulating a 20-degree beveled surgical resection. The sections were digitally imaged at x 50 magnification, and canal dimensions were measured using imaging software. The prevalence of two canals was 2% at 1 mm, 0% at 2 mm, and 1% at 3 mm. At these levels in the roots, the canal was rarely divided by hard tooth structure. An isthmus of tissue was present 20% of the time at 1 mm, 30% at 2 mm, and 55% at 3 mm. Four distinct canal types were noted: (i) round, (ii) oval, (iii) long oval, and (iv) ribbon. In 75% of the teeth, the canal shapes varied from one level to the next. The more coronally the root-end resection was made, the more elongated the canal tended to become.