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Mandibular Growth and Disc displacement of TMJ

Lateral Deviated Mandible

Temporomandibular disorders with mandibular deviation and facial asymmetry in adolescence

Bite and Temporomandibular Disorder (TMD)

Condylotomy

Temporomandibular disorders with mandibular deviation and facial asymmetry in adolescence

Facial asymmetry is a common type of dentofacial deformities. The clinical signs include asymmetry between the left and the right part of the face, the mid line of the upper teeth not aligned to that of the lower ones and skewed chin. The study of Haraguchi et al. investigating 1800 patients who underwent orthodontic treatment found 1135 subjects exhibited chin deviation. The study of Ramirez-Yanez investigating panoramic dental films of a random sample of 327 children aged 8-12 years old showed that 53.52% of the subjects had moderate to severe mandibular ramus height asymmetry and 49.24% of the subjects had moderate to severe mandibular body length asymmetry.
 

Etiology Analysis of Mandibular Deviation
 

The etiology of mandibular deviation remains under debate. Possible causes include congenital disorders, abnormal growth and development, as well as acquired TMJ disorders and trauma. Internal derangement of TMJ in particular shows high correlation with mandibular hypoplasia.
 

The first study focused on the correlation between mandibular deviation and TMJ disc displacement was published in 1966. Boering reported a 13.5-year-oold female patient with right TMJ disc displacement developed mandibular deviation during the 2-year follow-up period as the left mandibular condyle grew normally but the right mandibular condyle showed premature cessation of growth and mild bone resorption. Since the 90', more attention has been paid to the correlation between mandibular deviation and TMJ disc displacement. TMJ disc displacement was considered one of the important contributing factors to mandibular growth restriction.
 

As mentioned above, TMJ disc displacement in adults may develop degenerative joint disease (DJD) leading to condylar resorption, while in adolescents may lead to not only condylar resorption but also mandibular growth restriction, retrognathia and more profound signs of shortened mandibular length.

Adolescent TMJ Disc Displacement

TMJ disc displacement affecting mandibular development and growth is rare in children but common in adolescents (prevalence about 10-80%).  

Adolescent TMJ disc dislocation may not show any clinical or warning signs. Ribeiro found that among a population of 6-25 year-old adolescents, 34% who didn't show any signs of TMD had TMJ disc dislocation, and 86% who showed signs of TMD (TMJ clicking, pain when chewing or restriction in mouth opening) had TMJ disc dislocation.
 

It has been proven that TMJ disc dislocation will affect mandibular growth but may not show signs in adolescents. Clinical practitioners should pay more attention to its appearance.

TMJ Disc Displacement and Mandibular Growth

MRI techniques have become more popular and many in-depth studies investigating the correlation between TMJ disc replacement and mandibular growth were conducted in recent years. The study of Nebbe et al. investing the MRI and X-ray images of 189 adolescent patients aged 10-17 years old (with a mean age of 12.8) found a negative correlation between the extent of disc displacement and the growth of mandibular ramus height, meaning that more severe the disc displacement, the greater the restriction of mandibular growth. 。Zhuo The study of Zhou et al. conducted in Shanghai, China investigating the growth of mandibular condyle between the affected side and the healthy side by MRI on 124 adolescent patients (with a mean age of 16) with unilateral disc displacement without reduction during an averaged 13.6-month follow-up period found the continued condylar growth in the healthy side (condylar process length=26.07-26.82mm) compared to the decrease in the affected side (condylar process length=24.22-23.81mm). This indicated that TMJ disc displacement not only inhibited the growth of mandibular condyle but also caused condylar resorption. This study also suggested that even the clinical signs (e.g. pain while chewing, restriction of mouth opening) of the patients with disc displacement without reduction relieved with time, the condylar resorption might continue leading to a higher risk of mandibular deviation.。
 

In addition, animal experiments conducted by Legrell et al. (1998) and Bryndahl et al. (2008) investing the left-right difference in mandibular growth in rabbits with unilateral JMC disc displacement induced surgically found that unilateral disc displacement resulted in asymmetrical growth of mandible, significant decrease in length or height of affected side mandible, leading to mandibular deviation.。

Treatment of TMJ Disc Displacement

Many clinical studies indicated that for adolescent patients with TMJ disk displacement, early diagnosis coupled with minimally invasive disc reposition surgery could prevent or slow down its advert effects on mandibular growth (e.g. retrognathia, mandibular deviation and malocclusion).
 

Regarding the treatment options for adolescent patients with TMJ disk displacement (in particular without reduction), if the patients exhibit obvious degenerative changes or left-right difference in mandibular growth, minimally invasive surgical approaches should be applied to replace the disc back to normal anatomical position (Wolford, 1999; 2003; 2015), so as to prevent worse dento-facial deformity.