Computed tomographic analysis of the position of the mandibular canal in unilateral temporomandibular joint ankylosis patients

The aim of this study was to investigate the position of the mandibular canal through the region of the mandibular angle and body using computed tomographic (CT) imaging, and to relate the findings to those in the molar region on the ankylosed temporomandibular joint (TMJ) and the normal side. The mandibles of 25 patients with unilateral ankylosis of the TMJ (14 women and 11 men) were recorded on coronal CT slices 2 mm thick. All patients included in the study had had ankylosis diagnosed before they were 16 years old. The position of the mandibular canal was studied from the region of the third molar to that of the first molar on ankylosed and normal mandibles. The following variables were measured: the distance between the external surface of the buccal cortical plate and the outer surface of the mandibular canal (B); the distance between the external surface of the lingual cortical plate and the outer surface of the mandibular canal (L), and the distance between the external surface of the inferior border of the mandible and the outer surface of the mandibular canal (I). Our results suggest that changes are more pronounced in the regions of the second and third molars. The mandibular canal is closest to the inferior border of the mandible in the region of the second molar and farthest in that of the third molar. The greatest distance between the outer surface of the mandibular canal to the external surface of the buccal cortex on the ankylosed and normal sides was found in the first and second molars, and it was greater on the normal side. To minimise the risk of injury to the inferior alveolar nerve, the measurements of B, L, and I should be considered separately on the ankylosed and normal sides when planning mandibular osteotomies for distraction osteogenesis and orthognathic surgery, and when using monocortical screws.