Objective To investigate the influence of preoperative orthodontic treatment on the position and morphology of the articular disc and condyle in patients with class Ⅲ malocclusion.

Methods Forty patients with skeletal class Ⅲ malocclusion were selected as the study subjects.On the MRI of temporomandibular joint, superior joint space, anterior joint space and posterior joint space were detected to determine the position of condyle; condylar length, condylar width and condylar height were measured to determine the shape of condyle; the position and shape of the articular disc were determined through direct observation.The changes in the position and morphology of the articular disc and condyle before and after orthodontic treatment in patients with skeletal class Ⅲ malocclusion were compared.

Results In patients with skeletal class Ⅲ malocclusion, the superior joint space in the left and right sides before orthodontic treatment was smaller than that after orthodontic treatment; the anterior joint space, posterior joint space and medial joint space in the left and right sides before orthodontic treatment were bigger than those after orthodontic treatment, but the differences of which were not statistically significant (P>0.05).After orthodontic treatment, the joint space index in the left and right sides increased compared with before orthodontic treatment, which tended to the anterior position, and still in the central range, but the difference of which was not statistically significant (P>0.05).After orthodontic treatment, the condylar width, condylar height and condylar length in the left and right sides decreased compared with before orthodontic treatment, but the difference of which was not statistically significant (P>0.05).The number of patients with posterior temporomandibular joint disc position was the highest, the number of cases of this type decreased after orthodontic treatment, and there was no statistically significant difference in the proportion of patients with four different joint disc positions before and after orthodontic treatment (P>0.05).Before orthodontic treatment, patients with a double concave joint disc shape were the most common, followed by a double planar joint disc shape, and there was no statistically significant difference in the proportion of patients with two different joint disc shapes before and after orthodontic treatment (P>0.05).

Conclusions The current preoperative orthodontic plan has little effect on the position and morphology of the articular disc and condyle in patients with class Ⅲ malocclusion.