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Values for eleven orthodontological parameters were obtained in 42 cases of TMJ arthrosis in girls (T group; averageage: 15 years 11 months) who sought examination at the Department of Oral Surgery at the Attached Hospital of the Nagoya University School of Medicine, the Department of Oral Surgery at the Fujita-Gakuen Health University Hospital and at the Lion Foundation for Dental Health. The values were also obtained in 49 control females (N group; average age: 18 years 2 months). The parameters studied were: 1. Angle's classification, 2.Σ 5-5 (mesio-distal crown diameter)(A), 3.Σ 3-3 (mesio-distal crown diameter)(B), 4. Basal arch length, 5. Basal arch width, 6. Coronal arch length, 7. Coronal arch width, 8. Inter canine length, 9. Inter canine width, 10. B. A. L./A, B. A. W./A, C. A. L./A, C. A. W./A, I. C. L./A, I. C. W./A. 11. I. C. L./B, I. C. W./B etc. The values obtained were subjected to stochastic analysis (t-test) and the following results were obtained: 1. With respect to Angle's classification in the T group, 9.5% were found to have normal occlusion and 45.2% were found to be Angle II cases. In the N group, 30.6% had normal occlusion and 14.3% were Angle II cases. 2. Maxillary basal arch length in the T group was 19.826±2.9081mm, while mandibular basal arch length was 18.3667±4. 7735mm. In the N group, maxillary basal arch length was 23.2775±2.6377 mm, while mandibular basal arch length was 20.2877±4.1162 mm. Therefore smaller values were obtained in the T group. 3. With respect to occlusion status, abnormalities in the dental arch analysis were found to be frequent among normal occlusion, Angle I and Angle III cases in the T group. 4. Abnormalities in the dental arch analysis were not found in Angle II cases.

54 cases were diagnosed as temporomandibular joint arthrosis in young people at Nagoya University (Dent-Oral Surgery, School of Medicine), Fujita-Gakuen Health University (Dent-Oral Surgery, School of Medicine) and Lion Foundation for Dental Health between April 1983 and September 1985 (2.5-year period). They were studied in terms of clinical statistics, yielding the following results.1. The percentage of subjects at Hellman's occlusal developmental stage IV A was 87.0 %in patient group and 80.0% in normal group. The mean age was 15.8 years old in patient group, 17 years old in normal group.2. Angle's classification II and III were seen in 42.6% and 29.6% of patient group, 15.0% and 3.3% of normal group.3. The percentage of subjects with malocclusion was 90.7% in patient group, which was greater than that of normal group (60.0%). The most malocclusions in patient group were upper protrusion (29.6%) and crowding (53.6%). In normal group, 20% had upper protrusion and 33.4% had crowding.4. Of the subjects in patient group, 25.9% had 31 dentes, which was greater than the 11.7% having 31 dentes in normal group.5. In patient group, 22.2% had 3 third molars and 7.4% had 1, which exceeded normal group, in which 11.7% had 3 and 6.7% had 1. In 42.6% of patient group the dentes were asymmetric and in 31.5% of those cases the asymmetry was both vertical and horizontal.In normal group, the corresponding percentages were 26.7% and 16.7% respectively.

The subjects were 29 patients under 20 years old (6 males and 23 females: T-group) of TMJ arthrosis who visited the Department of Oral Surgery at Nagoya University Hospital, the Department of Dent-Oral Surgery at Nagoya University Branch Hospital and the Lion Foundation for Dental Health.They were classified on the relation of the first molars occlusion with their plaster models of dentition. And so, on their cephalograms, 16 angular, 11 linear measurements and 6 ratio of two lines were analized and compared with those of 117 females under 20 years who did not have TMJ arthrosis (N-group).The following results were obtained:1. The result of classification of their occulusion showed no existence of normal occulusion and Angle class I: 7 (male O, female 7·T-I), calss II: 15 (m. 4, f. 11: T-II), class III: 7 (m. 2, f. 5: T-III)2. On T-I group, frontal growth of the maxilla and the ramus height of the mandible were apparently inferior to those of N group, the mandibular plane angle was larger, and the mandible showed clockwise rotation.3. On T-II group, low frontal growth of the maxilla, more uprighting of the upper central incisor, and low growth of the ramus height and the mandibular body length, and clockwise rotation and retrusion of the mandible were observed.4. On T-III group low frontal growth of the maxilla was observed.From the results, it was guessed that TMJ arthrosis in young people of these patterns of the growth of maxilla and mandible were closely related to discordance with Mm.masticatorii or the lack of resting occulusion.