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Objective To explore the effect of attachment wear on tooth movement in clear Aligner treatment, and to provide references for improving the efficiency of orthodontic treatment. Methods The tooth cone bean computed tomography (CBCT) scanning data were obtained, and the tooth model was established and assembled with the worn and complete attachment, respectively. When the appliance applied 2° distal torsion, 0.25 mm distal displacement, 0.1 mm depression displacement and 0.1 mm elongation displacement to the teeth, the changes of tooth displacement, periodontal ligament stress and root equivalent stress in the worn and complete attachment groups were compared. Results When the clear Aligner was used to apply distal torsion and elongation displacement to the teeth, the maximum tooth displacement decreased significantly, and the worn attachment caused the teeth to move obliquely when the distal translation and elongation displacement occurred. When the tooth was subjected to distal torsion, distal translation, depression and elongation, the maximum principal stress of periodontal ligament and the equivalent stress of tooth root decreased when the worn attachment caused the tooth to be subjected to distal torsion, distal translation, depression and elongation. Conclusions Attachment wear will affect the efficiency of tooth rotation and elongation.When the attachments are obviously worn, they should be replaced in time to ensure normal function of the attachments.
RESUMO
Recommending postgraduate without tests is the path to improve the quality of postgraduate and choose talents with news ideas.In order to consummate the recommendation in local key medical college,the school of postgraduate in Hebei medical university formulated the selecting quota and standard scientifically and reasonably,selected the morally and academically excellent graduates,reasonably distributed quota of recommended exam-free postgraduates,reinforced cooperation between different colleges,explored the linkage among learning,studying and producing and attempted orderform talent-training model.
RESUMO
Objective To explore the location of the centre of resistance for the maxillary complex in cleft lip and palate by the use of finite element analysis. Methods Combining spiral CT scanning technology with the three-dimensional finite element method, a three-dimensional FEM model of LeFort Ⅰ , Ⅱ , and Ⅲ complex and soft tissue in cleft lip and palate was developed for analysis. Anteriorly and inferiorly directed forces of 9.8N were applied at five different levels parallel to the functional occlusal plane and four different levels perpendicular to the functional occlusal plane, respectively.For each loading condition, horizontal and vertical displacements of different anatomic points in the complex and on the maxillary dentition were analysed. Location of the centre of resistance in different osteotomy complex were studied. Results The resistant center of the LeFort Ⅱ complex in cleft lip and palate was located on intersection between basis nasi and medium of apertura piriforms vertically,apex of the canine and posterior point of the first bicuspid horizontally. The resistant center of the LeFort Ⅲ complex in cleft lip and palate was located on intersection between anterior of the nasion and medium of apertura piriforms vertically, posterior point of the first molar and first bicuspid horizontally. Conclusion Knowledge of the resistant center of different osteotomy complex could establish a basis for biomechanical studies of craniofacial complex distraction osteogenesis in cleft lip and palate.