Four hundred and eight patients with arthrosis of the TM J, who visited our clinic from January, 1987 to December, 1989 were classified into 5 types based on a newclassification proposal advocated by the Japanese Society of Temporomandibular Joint in 1986.
The patients consisted of 93 males and 315 females in the ratio of 1: 3. 4. Fifty-eight cases (14.2%) were classified into type I, 21 (5.1%) in type II, 263 (64.5%) in type III. 53 (13.0%) in type IV, 5 (1.2%) in others type and 8 (2.0%) were unclassified. In type III, 136 (33.4%) cases had an anterior disc displacement with reduction 103 (25.2%) had an anterior disc displacement without reduction, and 24 (5.9%) had an intermittent closed lock.
The sex ratio by type was 1: 3.5 in type I, 4.3: 1 in type II, 1: 4.0 in type III, and 1: 6.6 in type IV
The average age was 38.1 years old in type I, 41.7 in type II, 32.0 in type 11, and 54.6 in type IV. The average age was the lowest in patients with intermittent closed lock and the highest in type IV.
Even the cases of types II, III, IV frequently accompanied a pain at the masticatory muscies. The patients diagnosed as type II showed male predominance and a relatively acute course in their histories. According to arthrographic examinations performed on patients who complained of painful masticatory muscles alone and whose maximal interincisal distance was more than 40mm, it was revealed that these patients belonged to anterior disc displacement without reduction. The differentiation from type I was sometimes difficult only by clinical findings in such cases. The cases of which bone changes of the TMJ are not so rcmarkable and the discs are displaced, could not be clearly determined as either type III or type IV. The judgment of type II was most difficult because of its pain characters being the sole determinant.
The 4 cases classified into others type showed morphologic changes in the disc, such as perforation or adhesion, although disc displacement was not identified.
Although it is not easy to classify all of the cases only by their clinical symptoms, it is thought that the new classification proposal fundamentally has an advantage of simplifying the complicated etiology of arthrosis of the TMJ.
