The purpose of this study was to investigate the mechanical behavior of the human mandible in mastication for basic knowledge in order to understand the interrelationship between malocclusion and bone deformation.
For reproduction of accurate mechanical conditions, mechanical mastication robotics with viscous-elastic actuator controlled by a 32-bit computer system was used. Dry skulls were placed on this robotics, and muscle loading direction, forces and attachment area were determined from the information of Computed Tomographic data of living subjects. The mechanical strain generated on the surface of mandibular bone during mastication was measured by three axial electric strain gages.
The results were as follows:
1) On the application of light loading forces (Totalamount of 24N), the mandibular bone was bent from the anterior to the posterior part in the gonial region. Only two-dimensional distribution of strain around the loading area was demonstrated.
2) As for heavy force (Total 96N), a large amount of tension was generated from the anterior to the posterior part, the alveolar bone was inclined towards the lingual side, and inferior region of the rami was bent to the outside.
From the results, three-dimensional changes of strain and dynamics during mastication were demonstrated. These findings suggested that various biomechanical situations occurred in the mandible during mastication, and skeletal growth and/or bone formation might be affected by the mechanical behavior of muscle loading.
Therefore, the clinical diagnosis of dentomaxillofacial deformities should include careful consideration of the muscular performance and mechanical conditions.

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Five-year follow-up after mandibular distraction lengthening was performed on three cases with hemifacial microsomia (two unilateral and one bilateral). The patients were in the growth stage and orthodontic treatment using functional appliances with or without multi-bracket appliances were carried out in this period. The examinations focused on the changes of facial appearance and occlusion, and on development of teeth in the distracted areas. The findings were as follows:
1. In unilateral patients, facial asymmetry was improved immediately after distraction, while the occlusion became worse presenting lateral crossbites and open bites. After five-year follow-up, the occlusions were stable though they showed crowding. However facial asymmetry significantly recurred in one patient.
2. In the bilateral case, the effect of mandibular distraction was prominent. The facial profile and occlusion were improved markedly. Nevertheless, the subsequent orthodontic treatment with multi-bracket appliances, and mandibular osteotomies after the completion of facial growth were required to establish the final occlusion and to gain a good profile.
3. The development of teeth in the distracted areas showed various results, i. e., normal development, malpositioning and disturbance of root formation.
These findings suggested that although mandibular distraction was useful for the treatment of small mandibles, further refinement of this technique is required considering occlusal changes, recurrence of facial asymmetry and development of teeth.

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An occlusal reconstruction case with mandibular prognathism and loss of multiple teeth in presented.
The patient was a 30-year 3-month-old male whose chief complaints were esthetic dissatisfaction and speech disorder.
Sagittal splitting ramus osteotomy was used as the orthogathic surgery. The preoperative orthodontic treatment time was 11 months, and the postoperative 9 months.
This clinical report describes the orthodontic treatment of a patient with unstable occlusion due to mandibular prognathism and periodontal disease with loss of multiple teeth (754 457, 67).
The following special considerations were given to the treatment.
1) The patient had periodontal disease and was treated orthodontically after periodontal therapy.
2) During the entire treatment period, Plaque control was conducted thoroughly.
3) Postoperatively, a temporary denture was applied.
After orthogathic surgery, the patient's periodontal tissue condition was improved. It was suggested that orthodontic treatment can improve the periodontal tissue condition of a patient with periodontal disease and malocclusion.

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