A study on factors for determining terminal position of habitual jaw closures

Research Project

Project/Area Number	08457518
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	補綴理工系歯学
Research Institution	Tokyo Medical and Dental University
Principal Investigator	AI Minoru Tokyo Medical and Dental Univ., Faculty of Dentistry, Professor, 歯学部, 教授 (00013889)
Co-Investigator(Kenkyū-buntansha)	AKISHIGE Satoshi Tokyo Medical and Dental Univ., Faculty of Dentistry, Reseach Assistant, 歯学部, 助手 (30272602) BABA Kazuyoshi Tokyo Medical and Dental Univ., Faculty of Dentistry, Reseach Assistant, 歯学部, 助手 (80251536) YAMASHITA Shuichiro Tokyo Medical and Dental Univ., Faculty of Dentistry, Reseach Assistant, 歯学部, 助手 (80242212) SONEDA Kenji Tokyo Medical and Dental Univ., Faculty of Dentistry, Reseach Assistant, 歯学部, 助手 (10226714)
Project Period (FY)	1996 – 1997
Project Status	Completed (Fiscal Year 1997)
Budget Amount *help	¥6,600,000 (Direct Cost: ¥6,600,000) Fiscal Year 1997: ¥700,000 (Direct Cost: ¥700,000) Fiscal Year 1996: ¥5,900,000 (Direct Cost: ¥5,900,000)
Keywords	tooth contact / guiding cusp for retrusion / muscle activity / terminal point of habitual closure / 後方運動のガイド
Research Abstract	Reducing guiding cusps for the retrusive jaw movement sometimes leads mandible backward and makes the intercuspal position unstable. This study was performed to identify the phenomenon and to clarify its mechanism. 1. The tooth contact areas during retrusive jaw movement were investigated on 145 students, and found that the area which contacted most was the first premolar and the second molar followed. The unilateral contact accounted for more than 80%. The influence of guiding cusps for retrusive jaw movement on the terminal point of habitual closures was examined. A maxillary splint whose occlusal contacts were adjusted to natural dentition was applied to five subjects. And the distribution of terminal points of habitual closure with the splint, both with and without guiding cusps for retrusion, was observed longitudinally by using central-bearing equipment and CCD camera. The distribution of the terminal points on the horizontal plane was the same as those on the natural dentition wit … More h the cusp splint, while with the no cusp splint it displaced backward and approached the retruded jaw position after two or three days and it returned as before after removing the splint. The position of the condyle might go backward with no cusp splint. These results suggested the necessity of appropriate guiding cusp for the retrusive jaw movement. 3. The posterior displacement of the terminal points of habitual closure and the activities of masseter and temporal muscles were observed simultaneously by using the same procedures as previous investigation and EMG.Temporal muscle activities in keeping the mandible in the posterior position showed a tendency to increase in the period where the displacement of terminal points of habitual closure took place. 4. On the hypothesis that retrusive tooth contacts restricted posterior displacement of the terminal points of habitual closure, paths of habitual closure was ovserved with concerned teeth anesthetized. However a definite conclusion was not obtained yet. Less