Temporomandibular Joint Adaptations After Fixed Orthodontic Therapy in Cases Already Treated With Twin Block Appliance

Angle's class II division 2 malocclusion is subtype of Angle's class II malocclusion with unique facial, dental and craniofacial features which differentiate it from other malocclusions so much that it has been said to be a syndrome itself. Its frequency lies between 1.5 and 5% of all malocclusions found in a white western population. Hypertrophic masticatory muscles as documented in class II division 2 are directed in more anterior direction leading to increased magnitude of occlusal forces and hence increased TMJ loading. TMJ morphology depends, to an extent on occlusal loads acting on it, so class II division 2 malocclusion patients are expected to have specific TMJ complex morphology. Condyle position changes from anterior to posterior with age in class II division 2 cases. The use of functional orthopedic appliances to correct Class II malocclusions associated with retrognathic mandibles is indicated for the first phase of orthodontic treatment. A second phase of treatment is undertaken with fixed orthodontic appliances to obtain occlusal refinement. Although various investigations have shown the efficiency of this method of treatment, the mechanism by which the temporomandibular joint (TMJ) responds to the treatment is controversial.

Various techniques have been used to image the TMJ which include Magnetic Resonance Imaging (MRI), Cephalograms, Orthopantomograms , Tomograms , Bone scintigraphy with radiologic markers like 99mTc-MDP, Arthroscopy and Arthrography , CT scanning, Cone Beam Computed Tomography (CBCT).

Magnetic Resonance Imaging (MRI), a multiplanar imaging technique, has the advantage of giving an accurate assessment of both the bony and the soft tissues. This technique is believed to be non-invasive, radiation free and gives more superior contrast resolution than any other imaging modality. MRI is considered the imaging modality of choice for assessment of internal derangements of the temporomandibular joint. According to Akar et al "Bony structures and especially soft tissues of the TMJ can be examined by means of MRI and the relations of the tissues with each other can be evaluated." MRI studies have been done on fixed functional appliances which show significant displacement of condyle during treatment but later condyles returned to pre treatment positions at the end of fixed functional appliance treatment. Results documented in fixed functional appliance may not be same in removable appliances. Effects of removable functional appliances on the condyle-glenoid fossa (C-GF) complex have been studied with respect to the Frankel, Activator, Twin block and Bionator appliances. Franco et al found that Frankel therapy resulted in a 'more normal' articular disc morphology. Arat et al. concluded that disc positions were insignificant after 6 months of Activator therapy Chintakanon et al. concluded that Twin Block therapy had neither positive nor negative effects on disc position, and there was little evidence that the disc was recaptured. They also noted anterior positioning of the condylar head (CH) in the glenoid fossa after 6 months of Twin Block therapy. It should be noted that all of above studies are limited to the phase of removable functional appliance therapy only in Class II division 1 and no MRI study has attempted to evaluate the changes in the position of the Condyle-Glenoid Fossa (C-GF) complex treated with removable functional appliance therapy, followed by fixed orthodontic treatment in Class II division 2 malocclusion.

Aidar et al have studied changes in temporomandibular joint disc position and form following Herbst and fixed orthodontic treatment and found that at the end of the bi-phasic treatment the position and form of the initial articular discs were maintained. Kinzinger, et al. studied the effects of fixed orthodontic treatment in the case of skeletal class II on the position of the articular disc and condyle using MRI on 20 subjects and concluded that treatment did not alter the position of articular disc and even noticed an improvement in the anterior disc displacement in 8 joints out of 40. No studies have been done on bi-phasic treatment of skeletal class II, Angle's class II division 2 involving removable functional appliances in the first phase followed by fixed orthodontic treatment in second phase.

Therefore, the aim of this study is to document the changes brought about in the internal anatomic relationships of the TMJ complex , positional changes of glenoid fossa with respect to adjacent cranial structures after completion of fixed orthodontic treatment in adolescent females initially treated with removable functional appliances for skeletal class II, Angle's class II division 2 malocclusion,