[Study of internal reaction on the maxilla by orthopedic force].

For the purpose of analyzing deformations and movements in the maxilla loaded by orthopedic force to the maxillary first molar, a three dimensional finite element model of the maxilla was constructed. For modelling of the maxilla, the right side of an adult Indian skull was used. Constructed model was composed of 1,108 solid elements and 1,195 nodes. Materials of this model was composed of compact bone, cancellous bone, teeth and sutures. Constraint condition was fixed adjacent bone side surrounded by sutures. Load was directed from upward to downward 30 degree, changing every 30 degree reference to occlusal plane. Volume of load were weighed at 1 kg for each directions. Results 1. At upward load, stress was transmitted through the lateral wall of the maxillary sinus. The posterior portion of the maxilla was displaced more upward than anterior. Each process of the maxilla and the maxillary sinus was deformed, however, there was no stress on the orbitary surface. 2. At upward 60 degree load, the maxilla was compressed simply to the direction of load. At the upward 30 degree load, it was compressed backward-downward and rotated clockwise together with bending. 3. At backward load, the maxilla was moved backward and rotated clockwise. At downward 30 degree load, the maxilla was moved backward-downward and rotated clockwise. Both loads bended anterior portion of the maxilla and compressed posterior portion. The center of rotation or bending fell on the line joining the frontal process and the zygomatic process. 4. Of all five directions, backward load showed the maximum value of displacement and upward showed the minimum. Concerning with the absolute value of principal stress, backward load showed the maximum and upward 60 degree load showed the minimum. 5. Concerning with the principal stress value of sutures, compressive stress were distributed equally at upward load. However, as the load went to downward direction, it caused stress concentration. Especially, compressive stress in the pterygopalatine suture and transverse palatine suture, extensive stress in the midpalatal suture were especially great.