Temporomandibular joint adaptations following two-phase therapy: an MRI study

To document the alterations within the condyle-glenoid fossa (C-GF) complex and the positional changes of the glenoid fossa in the cranium after removable functional appliance therapy and after the completion of fixed appliance therapy.

The Department of Orthodontics, Centre for Dental Education and Research, All India Institute of Medical Sciences, New Delhi, India. The study sample consisted of 12 growing children (eight girls and four boys) between 10 and 14 years of age with skeletal Class II division 1 malocclusion selected on well defined criteria.

All patients were treated with either the Twin Block or the Bionator appliance followed by fixed appliances. Mean total treatment duration was 28 months. The changes in and around the C-GF complex were evaluated using MRI at pre-treatment stage, after functional appliance therapy and at the completion of fixed mechanotherapy.

Forward condylar position within the glenoid fossa and articular disc retrusion with respect to the condylar head were statistically significant after functional appliance therapy. However, the condyles had a relatively concentric position within the glenoid fossa, while the articular disc resumed its pre-treatment position at the end of the treatment. Linear measurements from the centre of the external auditory meatus to the post-glenoid spine revealed a 1.3-mm forward relocation of the post-glenoid spine along the Frankfurt Horizontal plane.

Forward relocation of the C-GF complex seems to be one of the mechanisms of action of functional appliances, while the internal anatomic arrangement within the temporomandibular joint (TMJ) complex normalizes to its pre-treatment position.