Comparison of TMJ Disc-condyle-fossa Relationship, After Fixed Orthodontic Treatment of Adolescent Males With Skeletal Class II, Angle's Class II Division 2 Malocclusion Treated Initially With Removable Functional Appliance: an MRI Study.

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.. 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. 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.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.

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.