MRI ASSESSMENT OF THE NORMAL TEMPOROMANDIBULAR-JOINT WITH THE USE OF PROJECTIVE GEOMETRY

A new analysis, the Projective Invariant Analysis, was developed for t he evaluation of magnetic resonance images of the temporomandibular jo int. This method was used because it takes into account factors such a s linear and angular measurements that simple Euclidean geometric meth ods fail to address. Forty ''normal'' joints (20 subjects) and 65 ''ab normal'' joints were analyzed. Joints were defined as normal if they h ad a Class I skeletal pattern and a Class I occlusion. In addition, a history was obtained and a clinical examination was performed on each of these subjects to rule out any temporomandibular joint dysfunction, masticatory muscle myalgia, or cervicalgia. The images of the 40 norm al joints were compared with 65 previously taken images of 53 patients with conditions that had been diagnosed as anteriorly displaced disks with reduction. These two groups were compared with the use of the an alysis method described by Drace and Enzmann that uses angular measure ments. The groups were also analyzed with the use of a new method in w hich the structural relationships of the articular eminence, gleniod f ossa, mandibular condyle, and articular disk were related to each othe r using projective geometry. For the projective invariant analysis, a 95% confidence ellipse was constructed on the basis of the normal data . All but one of the 40 normal points fell within this ellipse, and on ly three of the 65 abnormal points were inside the ellipse. Both analy ses showed a significant difference between the normal and abnormal gr oups. However, the variance in the data was less with the new analysis than with the Drace analysis, and the new analysis was found to be mo re accurate than the Drace and Enzmann analysis. It was concluded that for a specific population of normal persons, there is a predictable r elationship that exists between the condyle, disk, and fossa. It was a lso concluded that projective geometry is more accurate than simple an gular measurements to describe the structural relationships between th e three-dimensional structures of the temporomandibular joint.