The effects of posterior retraction on the displacement of the maxilla

Yoo, Bo Yeong; Kim, Jong Chul

Abstract

Three-dimensional finite element model was made from adult skull to find desirable direction of retraction force to treat skeletal class II malocclusion. The retraction force of 400g was applied to the first molar. The direction of the force application was 23degrees downward, parallel, 23degrees upward and 45` upward to the occlusal plane. The stress distribution and the displacement within the maxilla were analyzed by three-dimensional finite element method. The findings obtained were as follows: 1. Maxillary first molar was displaced posteriorly and inferiorly in 23degrees downward, parallel, 23degrees upward retraction but it was displaced posteriorly and superiorly in 45degrees upward retraction. 2. ANS, A point and prosthion were moved posteriorly and inferiorly and pterygornaxillary fissure was moved posteriorly and superiorly. Clockwise rotation of maxilla occurred when retraction force was applied. 3. The degree of clockwise rotation of maxilla was greatest when the force was applied 23degrees upward to the occlusal plane and was least when the force was applied 23degrees downward to the occlusal plane. 4. Large tensile stress appeared in maxillary first molar and alveolar bone and the infraorbital region of maxilla when the force was applied 23degrees downward to the occlusal plane. Tensile stress was smaller as the direction of force move upward. 5. Large compressive stress was appeared in maxillary first molar and infraorbital region in 45degrees upward case and large compressive stress occurred in the posterior part of maxilla as the retraction force was upward.