| ObjectiveProtraction headgear was used to treat skeletal Class III malocclusion during the growth period. Its effect has been proved in clinical and animal experiments. But there are different views on suitable age to begin treatment and the affluence of different genders and ages. This research evaluated the changes treated by protraction headgear and the differences between genders and dentitions and the relationships of growth patterns and treating effects.Material and Methods36 patient treated by protraction headgear was chosen include 15 males and 21 females, they were further divided into two groups: mixed dentition (14) and early permanent dentition (22). The force applied was 400 g per side and the patients were asked to wear the appliance at least 14 hours everyday. Lateral cephalo graphs were taken before treatment and after the achieving of good over-bite and overjet.Lateral cephalometric graphs were scanned , landmarks were determined and indexes were measured by computer cephalometric measuring software, the data were analyzed by SPSS10. 0 statistic software, the hard tissue indexes pre -post treatment were analyzed with paired t test, the pre - post treatment position changes of cranial,facial skeletal and teeth were evaluated; Each index change was grouped by gender and age to detect the difference; the skeletal patterns effect on the treating effects were valued by correlation analysis between the changes of each indexes and the indexes reflecting skeletal saggital and vertical relationships.Results1 ,paired t test showed that there were no changes in the base cranial structure, both maxilla and mandible showed significant growth, the maxilla moved forward and the mandible rotated backward and downward, the saggital relation improved; The indexes reflect vertical relationships were all increased, the upper incisors were labial inclined and the lower incisors were lingual inclined.2,t test on changes of every indexes between mixed and permanent dentitions showed that early permanent dentition had more increase in the post facial height, while there were no significant differences between those of other indexes.3,t test on changes of every indexes between different gender showed that the forward movement and improvement of saggital relationship of male was larger than those of female, female had more lower incisors lingual inclination.correlation analysis showed that NSAr had negative correlations with the change of ANB, ANB had negative correlations with the increase of mandible , the improvement of saggital relationship , the lingual inclination of lower incisors and the change of upper lip position; among the indexes that reflect the vertical relationship, most of them had negative correlations with the change of PM - A, SNGoGn correlated with PM - Ad and Ul - SNd; ODI had negative correlation with the forward movement of maxilla,the lingual inclination of lower incisors and the improvement of saggital relationship as well as positive correlation with labial inclination of upper incisors.DiscussionsAnimal experiments and clinical researches have proved that protraction headgear can affect the craniofacial structure by moving the retrusive maxilla forward to improve the skeletal relationships and facial profile. It was shown in our study that, with protraction headgear, both jaws'length increased and skeletal saggital relationship improved significantly, the forward movement and length in-crease of maxilla and the downward and backward-rotation of mandible could account for those change; in the respect of teeth, the lingual inclination of lower incisors and labial inclination of upper incisors were the compensation for the former malocclusion, from which we could conclude that the therapy effect was the results of change in bones as well as teeth, that was coincide with the former studies. The increase of vertical indexes showed we should be caution when treating high angle patients with the tendency of openbite.Many studies had different views on the...
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