The retromolar canal and its variations: Classification using cone beam computed tomography

To determine the prevalence of the retromolar canal and its various patterns using cone beam computed tomography (CBCT).

CBCT images with the presence of mandibular third molars from August 2013 to May 2015 were retrospectively investigated. The presence of retromolar canal, its patterns, sides, as well as gender were evaluated by two observers. The pattern of retromolar canal was initially classified into three types: Type A, superior type; Type B, radicular-retromolar type; and Type C, dental type. During the investigation, two additional types were found and further classified: Type D, plexus type; and Type E, forward type. The distribution of retromolar canals between genders and sides was statistically analyzed with Pearson's chi-square test.

A total of 201 mandibular sites in 156 subjects (99 women, 57 men) were included. Among them, 128 sites had retromolar canals (63.68%). The presence of retromolar canal was not statistically related to gender or side. Most of the retromolar canals were the radicular-retromolar type (Type B, 38.10%), followed by the superior type (Type A, 29.93%), dental type (Type C, 19.73%), plexus type (Type D, 6.80%), and forward type (Type E, 5.44%).

There was a high frequency of retromolar canals and these could be classified into five patterns. The clinician should be aware of this anatomical structure when performing surgical procedures involving the retromolar area.