Objective: To investigate the distribution of abnormal occlusion of permanent dentition in adolescents. Methods: 304 Junior university students aged 16- 18 years old were investigated with their occlusion casts according to the Angle classification and the relationshop of over-jet and over-bite in both anterior and posterior teeth. Asymmetrical Angle category was given to those whose bilateral classifications were different. Results: 19.73% of the subjects were found with normal occlusion. Among the abnormals 58. 05%, 8. 90%, 8. 90% and 24. 15% were found with Angle Ⅰ, Ⅱ, Ⅲ and asymmetrical Angle category respectively. Anterior edge-to-edge relationship, cross-bite, deep over bite, deep-over jet and open bite were 12.71 %, 11.02 %, 5.08%, 5.08 % and 2.12% respectively, posteriorly cross-bite, reverse crosss bite and combination of the two were 19.07%, 17.37% and 0.85 % respectively. Conclusion: The asymmetrical Angle malocclusion and abnormal over-jet and over-bite of both anterior and posterior teeth stand a large ratio in Junior university students.

砄bjectire: To investigate whether the disturbed occlusion can induce TMJ degeneration. Methods: 2 Rhesus female monkeys, 1 served as experimental animal and the other as the control, were included. Right mandibular first molar and left maxillary first molar of the experimental animal were extracted. Small strings were set at the missing space to pull the neighbor teeth inclined into the space and to occlude with opposite teeth in convex to convex relation. 8 months later condyles and discs of both animals were surgically obtained and prepared for scanning electron microscopy examination. Results: Gelatin like material was found over the condyle and disc surface of the control animal and obvious rigids were found on its articular surface. On the sagittal section of the condyle cells arranged in lines of each of the three layers of the soft tissue were observed. But on the top of the condyle surface of the experimental animal there was an area from media anterior to lateral posterior where the gelatin like material twisted or even disappeared here and there. There was an area where fibers were exposed. The soft tissue layers were thinner and the cellular layer was discontinued locally. The waves on the surface of middle and posterior part of the disc were disturbed and fossae like changes were found on the inferior surface. Conclusion: TMJ degeneration can be produced by gradually induced occlusal disturbance.

Objective:To investigate the effect of partial p osterior teeth with reverse cross-bite at one side of mandible on the chewing m ovement. Methods: 16 university students with partial posterior teeth reverse cross-bite and 12 with normal occlusion were included, 5 cycles o f gum chewing movement with left and right side separately were recorded with K6 -Ⅰmandibular kinesiograph (MKG) for the trace and velocity. Results: ①The chewing movement recorded in frontal plane was with a typical cycl e in controls while that in reverse cross-bite individuals was vertically in an d/or out type (59.38%), as well as in and out in same direction type (21.88%). ②Chewing movement in reverse cross-bite patients was in posterior direction, together with a larger angle of closing trace to horizontal plane and higher che wing terminal velocity. Conclusion: Partial posterior teeth with reverse cross-bite at one side have significant effect on both direction and v elocity of chewing movement.

OBJECTIVEThe relationship between occlusion and temporomandibular disorders (TMD) remains disputed. The related epidemiological studies have been carried out focused on the occlusal characteristics in motion, for example in protrusion, retrusion or laterally extension and on some of malocclusion features. Very few studies were carried out on the intercuspal occlusion which is the most important occlusal relationship. Angle's classification of occlusion and the relationship of over-jet and over-bite are two prominent features now generally used in clinical practice for occlusal evaluation. In present study two kinds of features of occlusion were compared among TMD patients, malocclusion patients and university student volunteers, who of the laters represented nature population.

METHODS100 continued cases visiting our TMD Clinic during the year of 2 000 with complain of TMD problem, 100 malocclusion patients in continued orthodontic department records, and 268 university student volunteers were included. All subjects were with complete dentitions, except of age-related third or second molar tooth eruption difference. Study cast were obtained for all 468 subjects involved and following characters were studied. 1. Angle's classification; 2. Over-jet and over-bite relationship. Anteriorly it included cross-bite, cusp-to cusp bite, deep over-bite (without deep over-jet), deep over-jet (with or without deep-bite), open bite, and others. Posteriorly it included cross-bite, reverse cross-bite and others. 3. Abnormal occlusal index: For the purpose of quantitatively comparing the abnormal occlusal relationship of over-bite and over-jet, the occlusal index was introduced. The anterior continued abnormal was scored as 3 while posterior continued oclcusal abnormal scored as 5. The sum of the scores in the same subject was taken as his abnormal occlusion index.

RESULTS1. Ratio of Angle's I patients in malocclusion group was significantly lower than those in TMD group and US group (P < 0.05), while the later two groups had no difference (P > 0.05). 2. The ratios of anterior cross-bite and deep over-jet were higher in malocclusion group than those in other two groups. No significant difference for the other kinds of abnormal over-jet and over-bite relationship were found among the three groups. 3. The abnormal occlusion index of malocclusion group was higher than that of US group, but not than that of TMD group which had no difference with US group either.

CONCLUSIONS1. Aesthetic related anterior abnormal occlusion such as anterior cross-bite and deep-over-jet attract more attention of popular. But they had no relationship with TMD. 2. TMD patients had not significant occlusal features on Angle's classification and over-jet and over-bite relationship compared to malocclusion and nature population subjects.

Dental Occlusion ; Humans ; Malocclusion ; epidemiology ; Students ; Temporomandibular Joint Disorders ; Universities