Positional Changes of Mandibular Canal Before and After Decompression of Cystic Lesions in the Mandible.

PURPOSE Significant displacement of the mandibular canal (MC), which occurs frequently in extensive mandibular cystic lesion cases, may raise the risk of inferior alveolar neurovascular bundle injury in surgery. The aim of the present study was to measure the association between positional changes of MC and the direction (in the coronal plane) of bone expansion of cystic lesions in the mandible. PATIENTS AND METHODS We performed a retrospective study of patients who had undergone decompression and enucleation surgery from January 2014 to December 2018. Based on coronal planes of cone-beam computerized tomography, the centroids of the expanded mandibles were calculated and considered markers for evaluation of the directions of bone expansion. In addition, the changes in the position of the MC before decompression and enucleation were measured and compared. A Cartesian coordinate system was introduced in this study to illustrate the relationship of positional changes between the displacement of the MC and expansion of the mandible in a straightforward manner. Statistical analysis was performed using the paired t test, unpaired t test, one-way analysis of variance or linear regression as appropriate. RESULTS Thirty-six patients with an average age of 29.8 years (14 men, 22 women) who received treatment of decompression and enucleation for mandibular cystic lesions were included in this study. The MCs were displaced in the direction toward the lower edge of the mandible and opposite to the direction of mandibular expansion. In addition, the MCs were relocated close to their "original location" by 1.67 ± 1.45 mm (mean ± standard deviation) approximately 1 year after decompression, accounting for 22.66% of the total displacement. CONCLUSIONS In mandibular cystic lesion cases, the MCs tend to displace opposite to the direction of mandibular expansion and relocate less after decompression.