Comparison of condylar position according to the amount of incisor retraction during orthodontic treatment : a cone beam computed tomography study

Abstract

Since the temporomandibular joint (TMJ) is an important anatomical structure in orthodontic field, there have been a lot of studies to investigate the relationship between temporomandibular disorder (TMD) and orthodontic treatment. However, it is difficult to identify the direct relationship between TMD and orthodontic treatment, which still remains a controversial issue. Most previous studies used TMJ tomograms that have limited accuracy because of superimposition and distortion. The development of computed tomography (CT) allows to obtain three-dimensional images of the condyle and joint spaces. The aim of this study is to evaluate changes in the condylar position during the orthodontic treatment using cone beam CT (CBCT). Sixty two patients who had visited a private clinic were divided into 3 groups (minimum, moderate, and maximum retraction groups) according to the amount of retraction of the maxillary incisor. Pre-treatment (T0) and post-treatment (T1) CBCT images were superimposed based on the anterior cranial base using OnDemand3D program. Four joint spaces (anterior, posterior, superior, and medial), condylar height, and ramus height were measured to evaluate the condyle position and compared between T0 and T1 using paired t-tests. In the minimum and moderate groups, there were no significant changes in the 4 joint spaces (P > 0.05), while in the maximum group the posterior joint space decreased by 0.2 mm during treatment (P < 0.05). However, the posterior joint space after treatment was still within a normal range. The condylar height and ramus height did not show statistically significant changes during treatment (P > 0.05). There was no significant relationship between condylar position and maxillary incisor retraction in the minimum and moderate retraction groups (P > 0.05). The orthodontic treatment does not significantly affect the condylar position. Although excessive retraction of maxillary incisors can affect the condylar position, the amount of backward movement of condyle is in a physiologic range.