Relationship between gonial angle and articular disk position of the temporomandibular joints: A retrospective study

Purpose: Magnetic resonance imaging (MRI) is frequently used to diagnose temporomandibular joint disease. However, very few studies have assessed the relationship between the mandibular gonial angle and temporomandibular joint (TMJ) disorders using panoramic radiography and MRI. The aim of this study was to assess the relationship between the gonial angle and articular disk position of the TMJs using panoramic radiography and MRI. Material and method: The patients underwent panoramic radiography and MRI simultaneously at a university hospital between April 2017 and March 2018. We analyzed the records of 109 patients with and without disc displacement. Among these, 88 patients had disc displacement of the TMJ, while 21 patients were normal. The variable “mean mandibular gonial angle” was evaluated as a predictor. The primary outcome was the presence or absence of disc displacement in the TMJs. The other variables included sex and age. Data were analyzed using Spearman's rank correlation coefficient, the Mann–Whitney U test, and receiver operating characteristic (ROC) curves. Statistical significance was set at P < 0.05. Results: There was no significant difference between men and women in mean gonial angle, and there was no correlation with age (P > 0.05). Moreover, the mean mandibular gonial angle in the disc displacement group was significantly higher than that in the nondisc displacement group (P < 0.01). ROC analysis revealed a cutoff mandibular gonial angle of 120.23° for predicting the development of disc displacement. Conclusions: Mandibular gonial angle is a useful parameter for predicting disc displacement of the TMJs.