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This study was designed to investigate stresses in the TMJ during clenching in patients with skeletal discrepancies in the vertical direction. A three-dimensional model of the mandible including the TMJ was used for finite element analysis for the stresses. The model, referred to as a standard model, consists of 2,088 nodes and 1,105 solid elements, comprising the cortical and cancellous bones, articular disc and cartilage layer, and periodontal ligament. The standard model was modified by varying the gonial and mandibular plane angles to simulate vertical discrepancies between the maxilla and mandible observed in open and deep bites. Stresses were analyzed on the surfaces of the condyle, the glenoid fossa, and the articular disc, and the values were compared to those found with the standard model. Stresses increased substantially for the condyle, the glenoid fossa, and the articular disc with greater gonial and mandibular plane angles, and those changes were more obvious in association with the divergent mandibular plane. Thus, the nature of stress distributions in the TMJ was substantially affected by vertical discrepancies of the craniofacial skeleton. It is also suggested that these changes in stresses produce a lack of biomechanical equilibrium in the TMJ, which may have some association with temporomandibular disorders.

Cross-sectional data were obtained from 1182 Japanese high school girls of 12 and 15 years old. The data were analysed for the prevalence of specific occlusal features and the prevalence of cardinal Temporomandibular Joint Dysfunction (TMJD) symptoms in different occlusion groups. The associations between occlusal features and TMJD symptoms were analysed by the Z-analysis. The results were as follows: the prevalence of TMJD symptoms (total) was about 23% in both age groups examined. Noise had the highest prevalence of the specific TMJD symptoms in both age groups (16% and 11%). With age and for different occlusion groups, there was a significant increase in deviation on opening (P < 0.001) and a decrease in pain and noise (P < 0.05). No significant associations were found between the occurrence of TMJD symptoms (total) and occlusal features in all the examined occlusion groups. With respect to specific TMJD symptoms, however, the investigation of the different groups revealed a significant association (P < 0.05) of intra-arch occlusal (crowding) features with the occurrence of deviation on opening and with the occurrence of the combined TMJD symptoms which include deviation on opening. This indicates that crowding may be an important sign for predisposing TMJD. For the other single disorder symptoms (except pain), we did not find a significant relationship (P < 0.05) with aspects of occlusion, which may confirm a multifactorial TMJD problem wherein occlusal features can have a contribution to TMJD.

The present study was conducted to investigate stress distributions in the maxillary complex from headgear forces by means of three-dimensional finite element analysis. A posteriorly-directed force of 1.0 Kgf was applied to the maxillary first molars in the directions parallel and 30 degrees inferior to the occlusal plane. In the lower regions resisting posterior displacement of the complex, large normal and shear stresses were observed. Meanwhile, the regions resisting upward displacement experienced larger than normal stresses. A downward force produced slightly larger stresses than a parallel force and varied the nature of stresses from compressive to tensile or vice versa in the temporozygomatic suture. Thus, the stress distributions in the sutures varied according to their anatomic locations relative to force directions. The maxillary complex exhibits postero-inferior displacement with clockwise rotation from the horizontal headgear force. This becomes more prominent as the direction of force becomes more inferior.

The association between malocclusion and the prevalence of temporomandibular disorders (TMD) was studied in an orthodontic patient population before orthodontic treatment was started. A total of 305 patients, 232 with general malocclusion and 73 who also had cleft lip or palate, were given a questionnaire about the subjective symptoms of TMD. Clinical examinations for type of malocclusion and TMD signs were also conducted. No significant differences in the prevalence of TMD were observed between the sexes or between the two patient groups. Temporomandibular joint sounds and difficulty of jaw movement were the most common of the TMD signs and symptoms. Open bite, posterior crossbite, and deep bite were the most prevalent types of malocclusion in both groups. Thus, some specific types of malocclusion were significantly associated with the occurrence of TMD.

Prevalences of malocclusions and dental caries in molars were investigated on a database of high school students collected between 1977 and 1986. A total of 6,665 schoolgirls were evaluated. The proportions of 54.1% in the seventh grade and 56.6% in the tenth grade students were judged as having malocclusions. The prevalences of dental caries for the lower first and the second molars were significantly higher (p less than 0.001) than those for the upper opponents during the observation period. The prevalence of dental caries increased linearly for all kinds of molars in accordance with age, but they were lower than those reported by the Ministry of Health and Welfare in Japan determined for the entire nation. The percent of dental caries for the second molars revealed abrupt increases from 10% at the seventh grade to 50% at the 12th grade. These changes were particularly noticeable between the eighth and the tenth grades. These results suggest the significance of oral health care education during the adolescent period based on a long-term cooperation made by dentists, school nurses, teachers through the participation of students into the oral health care programme.

Prevalences of malocclusions were investigated in a sample of 3,520 girls recorded between 1984 and 1986 at a private high school. Also, proportions of students who had received and were under treatment were surveyed for 3,501 students in 1989. In addition, ratios of a number of those who were judged to reveal maxillary protrusion with respect to that of the whole sample examined were evaluated as a function of overjet. The results of the surveys are as follows. SURVEY I) A total prevalence of malocclusion was 57.9% in the Grade 7 (G7) and 56.4% in the Grade 10 (G10). Among malocclusions surveyed, maxillary protrusion was found in 8.1% of the G7 and in 7.8% of the G10. Deep overbite was determined in 7.9% of the G7 and in 7.6% of the G10, mandibular protrusion was found in 2.4% of the G7 and in 2.7% of the G10. Edge-to-edge incisor relationships were determined in 6.4% of the G7 and in 7.6% of the G10. Anterior open bite was found in 2.4% of the G7 and in 2.9% of the G10. Crowding was found in 37.3% of the G7 and in 33.9% of the G10. SURVEY II) Prevalence of students who had orthodontic treatment at the time of survey, was 6.4% in the G7, 7.0% in the G8, 6.0% in the G9, 6.0% in the G10, 5.4% in the G11, and 3.6% in the G12. Those who had had orthodontic treatment revealed proportions of 8.1% in the G7, 8.0% in the G8, 7.7% in the G9, 11.3% in the G10, 12.2% in the G11, and 13.7% in the G12 students. SURVEY III) A proportion of 73.5% of those who had overjets more than 6 mm were judged to have maxillary protrusion.

The relationship between dentoskeletal and tongue soft-tissue variables has been quantified in a sample of 60 adult females with normal and anterior open-bite malocclusions. Three lateral rest-position head films were obtained for each subject. A principal component analysis reduced the data base and six significant canonical correlations were identified. The first canonical correlation (r1 = 0.962) represented a size-related correlation factor between the two groups of variables. Subjects with characteristics of a short face syndrome and some evidence of overbite had tongue tips positioned below the lower occlusal plane (r2 = 0.929). In contrast, skeletal open-bite subjects (r4 = 0.759) revealed tongue tips ahead of and above the lower incisor teeth with the mandible in the rest position. Undererupted mandibular teeth (r5 = 0.666) were associated with a reduced tongue height and an inferior epiglottis; short tongue length (r6 = 0.563) correlated with a linear combination of upright central incisors, a small overjet, a low ANB angle, unerupted maxillary and mandibular teeth, and a steep occlusal plane. The multivariate statistical analysis extracted clinically significant associations between tongue soft-tissue and dentoskeletal variables. Tongue posture at rest in skeletal open-bite subjects appeared to be related to incisor position.

Malfunction and abnormal posture of the tongue has been thought to be one of etiological factors for skeletal open-bite at length. In this study, an adult female patient with anterior open-bite is reported, who has been treated by means of posterior maxillary osteotomy and has obtained a good occlusion and profile, which is stable throughout the retention period. Electromyography was obtained from the tongue muscles by surface electrodes and the tongue muscle activity during deglutition was measured before and after surgery. The tongue posture was also analyzed on the basis of the roentgen cephalogram with the mandible at the rest position. Larger tongue muscle activities during swallowing was revealed compared to the control subjects. In addition, anteriorly and superiorly positioned tongue was seen in the initial stage. The amplitudes of the tongue muscle had decreased and tongue posture had shifted posteriorly and inferiorly following surgery, which approximated to the those observed in the control subjects. These improvements of the abnormal activity and posture of the tongue and the stability of occlusion after surgery confirmed that posterior maxillary osteotomy is an effective surgical operation for the anterior open-bite patients in terms of prognosis.

Methods for measuring tongue volume and the capacity of the oral cavity proper were devised. Analysis of the data on 25 females with normal occlusion revealed that the tongue volume significantly correlated with the capacity of the oral cavity proper and the depth of the floor of the mouth. [ABSTRACT FROM AUTHOR]