Background and aim: Fixed functional orthopedic appliances used in 6 to 9 month-long treatments to correct distoclusion keep the mandible permanently in the therapeutically-desired protruded position. The principal aim of this approach is to achieve an increase in length of the lower jaw by stimulating mandibular growth. Ideally, adaptive mechanisms in adolescents and young adults result in condylar remodeling. Alternatively, however, therapeutically-undesirable alterations in the condyle position within the articular fossa may also occur. Thus the aim of this magnetic resonance imaging (MRI) study was twofold: 1) to verify the effects that the treatment with a fixed functional orthopedic appliance used to correct distoclusion has on the topographic relationship of mandibular condyle and glenoid fossa, and 2) to analyze morphologic changes in the condyle.
Patients and methods: Treatment progress in 20 patients was monitored by MRI at four defined points in time. Visual inspection and metric analysis were performed in three planes (axial, frontal, parasagittal) shown on the MRIs. 3D-reconstruction of the condyle surfaces based on the MRI data sets at hand was done in selected cases.
Results: Upon assuming the therapeutically-desired position, the condyles were caudally and ventrally displaced from their centric position within the fossa. At the end of treatment, they had returned to their original position. When assessed laterally, statistical analysis revealed no significant differences between the joints on the right and left sides. Neither the anterior nor posterior joint space among all 40 joints exhibited significant changes in width compared to the baseline findings. Visual inspection in the axial, frontal, and sagittal planes revealed changes in the exterior form of 31 of the 40 condyles analyzed. On the whole, while morphologic changes were observed in all three planes, they were most marked in the axial plane. Metric analysis of the 2D-MRIs, on the other hand, revealed no significant changes in width, depth, or height in the plane in question. This is why we reconstructed the condyle structure three-dimensionally on a trial basis. For purposes of analysis, we super imposed the reconstructions of the condyle surfaces at the various control points on each other. By processing the data in this manner, an alternative approach for evaluating morphologic changes was created. CONCLUSIONS AND PROSPECTS: In patients treated with a rigid, fixed functional orthopedic appliance (FMA) for skeletal Class II malocclusion, both joints returned to a physiologic condyle-fossa relationship post-treatment. The improved occlusion was not achieved at the price of unphysiologic repositioning in the temporomandibular joint. Visual inspection suggested that morphologic changes in the condyle may have occurred as treatment progressed, but this was not confirmed by 2D metric analysis. However, by means of 3D-reconstruction of the condylar surfaces and their superposition, detailed visualization of adaptive mechanisms and their non-invasive evaluation in 3D may become feasible in clinical routine.