The evaluation of rotational movements of maxillary posterior teeth using three dimensional images in cases of extraction of maxillary first premolar / 대한치과교정학회지

Cephalometric superimposition is unable to evaluate tooth movement along the occlusal plane and the errors of photographing and superimposition of the occlusogram is also inevitable. The purpose of the present study was to evaluate the rotational movements of the maxillary posterior teeth following space closure after extraction of maxillary first premolars, using 3D dental images. In 19 adult females, analysis of rotational movements of the maxillary posterior teeth was performed between the initial and final 3D dental images superimposed on the maxillary hard palate. The results showed a diversity of rotational movements of posterior teeth. The causes of various rotational movements may be different rotation of molars in each case at the beginning of treatment, individual characters of the dental arch and tooth morphology. The results of the study indicate that accurate evaluation of rotational movements of posterior teeth following space closure after extraction of premolars using 3D dental images can be obtained through the subdivision of tooth movement during the initial aligning, space closure and finishing stages.

THE THREE DIMENSIONAL STRESS ANALYSIS ON VARIOUS DIRECTIONS OF THE MANDIBULAR CONDYLE MOVEMENT BY USING FINITE ELEMENT METHOD

The condyle head of mandible was usually influenced by the stressful forces generated from a voluntary movement of bone fragment after the sagittal ramus osteotomy which would be mainly performed for the mandibular deformity patient. In this study we measured the stress values exerted on condyle and evaluated which area of condyle had a more stress concentration while condyle head moved in X, Y and Z axis by using a 3 dimensional finite element model. The result were as follows: 1. On bodily movement, the value of maximum force was 40.98Kg/cm2 at the (-X) direction and the stress area was the center of superiposterior nonaticular area of the condyle. 2. On ratational movement, the value of maximum force was 173.1Kg/cm2 at the (+Y) direction and the stress area was the anterior area of condyle neck. 3. From the general point of view there were more stress on rotational movement than on bodily movement. 4. The stress concentration area was the condyle head on bodily movement and the condyle neck on ratational movement. 5. From the result of this study. We found out that this results were a correspondence with clinical predictions in which a condyle head got the most stress concentration only when a condyle head in the posterior rotational position during orthognathic surgery. 6. The results of this study show that we should consider not to place the condyle head in the posterior position and posterior rotational position during orthognathic surgery.