OBJECTIVETo analyze the effects on the morphology of temporomandibular joint (TMJ) of the adult with the low angle Class II malocclusions before and after orthodontic treatment comparatively. To provide the references for the orthodontic treatment of the adults.

METHODS19 adult patients with low angle Class II malocclusions were chosen and treated with Damon self-ligating braces. The examinations of 16-slice spiral CT were taken before and after the orthodontic treatment. The parameters of skeletal morphology of TMJ were measured in the multiplanar reconstruction (MPR) images. The results were analysed statistically.

RESULTSThe rate of condyles in a center position in the glenoid fossa after the treatment was 52.6%(20/38), and the rate of retrodisplacement was 31.6% (12/38). The position of the condyles before and after the orthodontic treatment had significant differences (P<0.05, chi2=4.41, chi2=5.32). The mean value of the anterior oblique angle of condyle decreased by 2.32 degrees +/- 1.78 degrees after treatment, meanwhile the average height of the condylar head increased by (1.07 +/- 0.29) mm. There were significant differences in both results before and after treatment (P<0.05).

CONCLUSIONThe orthodontic treatment can make the TMJ structures stable and beneficial to relieve the symptoms by moving the condyle forward, increasing the height and reconstructing the anterior oblique angle of condyle on adult patients with low angle Class II malocclusions.