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Objective To study the friction between brackets and archwires and the influential factors. Methods To test the friction of six combinations of canine bracket and stainless steel archwire, and to calculate the critical contact angles for each combination. Results The friction maintains stability with slight changes when the contact angle is smaller than the critical contact angle. The friction increases linearly when the contact angle is larger than the critical contact angle. The friction of different combinations of bracket-archwire are different and the critical contact angles are also different. Conclusion The critical contact angle influences the friction between bracket and archwire significantly. The critical contact angle is relevant to both the structure of the bracket and the size of the archwire.
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Objective To explore the feasibility and evaluate the teaching effect of case-based multidisciplinary team teaching mode in clinical practice teaching of gynecology.Method According to different grade,120 students were divided into experimental group and control group (60 students per group).The teaching content contained three malignant tumor cases,which were cervical cancer,endometrial cancer and ovarian cancer.The course needed 12 periods totally.The experimental group received multidisciplinary team (MDT) teaching mode,and the control group received traditional lecture-based learning teaching mode (LBL).Teaching effect evaluation and test scores would be analyzed at the end of teaching.SPSS19.0 was used for t test and chi-square test.Results Our results showed that the theory test scores,practical skills test scores,the paperwork scores and the total scores of the students in MDT group were significantly higher than those in the traditional group (P＜0.05).At the same time,the students' self-evaluation scores in the ability of information retrieval,acquisition,understanding,comprehensive and the ability of self-learning,learning interest,enthusiasm and teamwork were significantly higher than the traditional group (P＜0.05).Conclusion MDT teaching mode is feasible,which can improve teaching effect and students' quality,and is worthy of advocating and popularization.
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Objective:This study was based on digital orthodontic diagnosis work flow for indirect bonding transfer tray model design and three-dimensional (3D) printing, and the aim of this paper was to inspect the dimensional accuracyof 3D printed brackets, which is the foundation of the follow up work and hoped that will illuminate the clinical application of the digital orthodontics work flow.Methods: The samples which consisted of 14 cases of patients with malocclusion from Department of Orthodontics Peking University were selected, including 8 cases with tooth extraction and 6 cases without tooth extraction.All the 14 patients were taken intra-oral scan (Trios 3Shape,Denmark)and cone-beam computed tomography (CBCT, NewTom 3G volumetric scanner, Aperio Service,Italy)shooting after periodontal treatment.STL data and DICOM data were obtained from intraoral scans and CBCT images.Data segmentation, registration, fusion, automatic tooth arrangement, virtual positioning of orthodontic appliance and conversion the coordinates of malocclusion model were all done with self-programming software.The data of 3D printing model with brackets on it were output finally and printed out with EDEN260V (Objet Geometries, Israel) to make indirect bonding transfer tray.Digital vernier caliper was used to measure the length and width of upper and lower left brackets and buccal tubes on those 3D models after removal of surrounding supporting material by ultrasonic vibration and water-spray.Intra-examiner reliability was assessed by using intra-class correlation coefficients (ICC), and one-sample T test was used to compare the measurements with the standard dimensional data of the brackets.Results: There were significant differences which range in 0.04-0.17 mm between the 13 items out of the 19 measurement items.Except for the length of the lower left premolars''brackets, mean values of the other items were greater than the test value.Conclusion: Although the measurement results in the width of brackets and the width and length of the buccal tubes obtained experimentally were slightly larger than the test value,this may not reduce the accuracy of indirect bonding procedure in clinic necessarily.Whether the differences which range in 0.04-0.17 mm would actually affect the retention and positioning of brackets needs to be confirmed by further studies.