Magnetic resonance imaging assessment of positional relationship between the disk and condyle in asymptomatic young adult mandibular prognathism.

The aim of this study was to clarify disk position relative to the condyle and condylar position relative to the glenoid fossa in clinically asymptomatic and orthodontically untreated young adult Class III patients by magnetic resonance imaging (MRI). In addition, the relationship between skeletal Class III morphology and positional changes of the temporomandibular joint (TMJ) components were investigated. The material consisted of 34 bilateral sagittal oblique TMJ MR images (MRIs) and lateral cephalometric radiographs taken in a closed mouth position. The mean age of the patients was 20.71 +/- 0.82 years (range 16-29 years). Only clinically symptom-free subjects were included in this study. Measurements made on the MRIs and lateral cephalographs were used to calculate means and minimum and maximum values. The right and left TMJ variables were compared with the Student's t-test. Correlation coefficients between bilateral TMJ variables and skeletal variables were calculated. In the right TMJ, the disk was positioned anteriorly and the condyle was positioned posteriorly, whereas the left TMJ was normal. A negative correlation existed between the vertical skeletal morphology and the anterior joint space of the TMJ. A positive correlation was found between the left disk position and the vertical skeletal morphology because of the differentiation of the condylar head angle in each side. As a result, clinically asymptomatic Class III patients may be candidates for TMJ derangements. For this reason, clinical and visual examinations should be performed simultaneously to eliminate diagnostic errors before orthognathic treatment.