RESUMO
Objective To investigate the influences of loading time and loading angle on the stress, displacement of human periodontal ligament in dynamic jaw. Methods The three-dimensional assembly model of the mandible front teeth, periodontal ligament and alveolar bone was reconstructed by using the reverse engineering technology. The thickness of periodontal membranes was 0.2 mm. The stress, displacement at different positions of the periodontal ligaments during different jaw cycles were analyzed under dynamic load in the direction from bucca to tongue side with 0°, 15°, 30°, 45°, 60°, 75°, 90° angle to the long axis of the tooth. Results During one jaw cycle, the ratio of the maximum to minimum value of the maximum residual stress due to different loading angles was 5.5, and the ratio of the maximum to minimum value of the maximum displacement was 8.1. The ratio of the maximum to minimum value of the maximum displacement which was caused by five jaw cycles was increased in the range from 1.02 to 1.35 with the increase of loading angles. The ratio of the maximum to minimum value of the maximum residual stress which was caused by different loading angles was increased in the range from 1.86 to 3.00 with the increase of jaw cycles. The location of the maximum stress was at the tongue side of the cervical margin at different loading angles, and the location of the maximum residual stress was distributed at different positions of the cervical margin. Most stress was accumulated at the root of the periodontal ligament under the 0° dynamic load. Conclusions The situation of the accumulated residual stresses and the uncertainties in the distribution of the maximum residual stresses should be observed in the clinical choice of mandible incisors fixed by bridge abutments; large angle force applied to the tooth was harmful to the periodontal ligament and rapid succession of chewing hard food should be avoided as much as possible during the clinical treatment.
RESUMO
<p><b>OBJECTIVE</b>The aim of this study is to investigate the changes of hard tissue profile in anterior-posterior and vertical direction in bimaxillary protrusion patients after orthodontic treatment.</p><p><b>METHODS</b>A total of 24 bimaxillary protrusion patients (male 8, female 16), aged from 11.2 to 29.0 (average 16.9 years old), were selected to be treated with standard edgewise technique consisted of 4 first premolars extraction. Cephalometrics were taken before and after treatment. The changes of hard tissue profile were studied using the computer-aid X-ray cephalometric analysis.</p><p><b>RESULTS</b>1. The length of the maxillary and the mandible increased significantly, but the anterior-posterior relationship of the maxillary and the mandible did not change significantly. 2. The anterior and posterior facial height increased significantly, but the ratio of anterior and posterior facial height and the angle of MP-FH which reflected the inclination of the mandible plane did not change significantly. 3. The height of the upper and lower first molar increased significantly along with the increase of the anterior and posterior facial height. 4. The height of the upper incisors increased significantly, but the height of the lower incisors decreased significantly.</p><p><b>CONCLUSION</b>The anchorage in anterior-posterior and vertical direction were controlled preferably, the patients did not manifest disadvantageous vertical growth trend.</p>