Positional Relationship of TMJ Disk in relation to Glenoid Fossa

Objectives:The purpose of this study was to evaluate the positional relationship of the TMJ disc and condyle in relation to the glenoid fossa in patients with normal disc position, partial anterior disc displacement (ADD), ADD with reduction, and ADD without reduction using MRI. Methods: 301 TMJ MRI images of 152 patients with a past history of TMJ disorder who visited the Department of Orthodontics, Seoul National University Dental Hospital. For the condyle, a line 1 cm from the tip of the condylar head was drawn parallel to the reference line. This was traced on acetate paper, then scanned at a resolution of 300. The degree of disk displacement and reducibility were categorized into 4 groups: 1, Normal; 2, Partial anterior disk displacement (ADD); 3, Full ADD with reduction of the disc; 4, Full ADD without reduction. The association between each group and the position of the condyle and disk in relation to the glenoid fossa were evaluated. Results:In patients with ADD with reduction, the condylar head was found to be positioned posteriorly within the fossa compared to the normal group.The posterior position of the condyle returned to a more concentric position with further displacement of the disc (ADD without reduction), to resemble the normal group.There was no statistically significant difference in the vertical position of the condyle. This may be related to resorption of the articular eminence leading to vertical changes in the reference line.Conclusion:The horizontal and vertical position of the disc was found to be statistically significant for all groups. The disc moves in a downward and anterior direction with advancing disc displacement.