Will unilateral temporomandibular joint anterior disc displacement in teenagers lead to asymmetry of condyle and mandible? A longitudinal study

To evaluate the change of morphological symmetry of the temporomandibular joints (TMJ) during natural course of unilateral juvenile anterior disc displacement (UJADD) by comparing the ipsilateral joint with the contralateral side; and to analyse its effect over mandibular asymmetry (MA). This study is a self-control longitudinal study. Consecutive UJADD cases with no history of TMJ infection, injuries to the jaws, or congenital, developmental and systematic disorders that may affect the craniofacial growth were collected and followed for at least 6 months. Patients' age at both first visit and revisit was recorded. Pictures of magnetic resonance imaging (MRI) were selected to measure the differences between bilateral condylar height, disc length and condyle-disc distance, and comparison of the measurements before and after follow-up were made. Meanwhile, posteroanterior cephalometric radiographs (PA) were taken and deviation of menton from facial midline was measured before and after follow-up. Severity of MA was divided into 4 stages according to menton deviation: Non-MA (<2 mm), Minor-MA (≥2 mm, <4 mm), Medium-MA (≥4 mm, <6 mm), and Major-MA (≥6 mm). The constituent ratio of MA was evaluated and correlation between TMJ morphological change and asymmetry of the mandible was analysed. Forty four patients were included, with a mean follow-up of 12.22 months. The average age was 16.31 years old (range, 10–20 years) at first visit. Significant progression of disc displacement was found: condyle-disc distance increased, disc shortened and difference between bilateral condylar heights increased. Along with this, occurrence of MA increased from 86.36% to 93.18%, and average menton deviation increased from 5.58 mm to 7.74 mm after follow-up. The correlation coefficient (CC) of increase of condylar height difference and development of MA was 0.681 (p < 0.05). Also, increase of menton deviation was significantly related to age of the patients (CC = −0.760, p < 0.05). The results show that UJADD result in asymmetric growth bilateral TMJs, especially condylar height, which was much shorter on the ipsilateral side. In the same time, MA got worse during the natural course of UJADD. It is concluded that UJADD was one of the major causative factors of MA.