[The relationship between the movement of molars and the transmitted mechanism of orthodontic forces in extraoral anchorage (2)].

Abstract

The relationship between the movement of molars and the transmission of orthodontic forces were especially studied about the upward pull of the outer bow in extraoral anchorage. Molar movements were theoretically analyzed from horizontal pull to upward angle of 40 degree. The transmission mechanism of the orthodontic force was studied from horizontal pull to 40 degree upward angle on each 5 degree with the holography experiment on a human dry skull. 1. Horizontal pull of the outer bow resulted in distal movement of the molar. The long axis of the molar was tipped distally. The dentofacial cranium transformed to the lower and backward direction. 2. When the outer bow was inclined at an upward angle of about 18 degree, the molar moved bodily to the distal and superior direction. But the dentofacial cranium transformed a little to the lower and backward direction. 3. When the outer bow was inclined from 25 to 30 degree upward angle, the molar rotated to the clockwise direction, and the dentofacial cranium rotated to the counter clockwise. The bending deformation was not observed on the dentofacial cranium. 4. The dentofacial cranium was compressed in the pull direction from 25 to 30 degree upward angle. These directions were clinically interpreted as inhibition of the downward and forward growth of the maxillary bone.