The locking mechanism between bracket and shape memory alloy (SMA) archwire in the newly developed domestic orthodontic device is the key to controlling the precise alignment of the teeth. To meet the demand of locking force in clinical treatment, the tightening torque angle of the locking bolt and the required torque magnitude need to be precisely designed. For this purpose, a design study of the locking mechanism is carried out to analyze the correspondence between the tightening torque angle and the locking force and to determine the effective torque value, which involves complex coupling of contact, material and geometric nonlinear characteristics. Firstly, a simulation analysis based on parametric orthogonal experimental design is carried out to determine the SMA hyperelastic material parameters for the experimental data of SMA archwire with three-point bending. Secondly, a two-stage fine finite-element simulation model for bolt tightening and archwire pulling is established, and the nonlinear analysis is converged through the optimization of key contact parameters. Finally, multiple sets of calibration experiments are carried out for three tightening torsion angles. The comparison results between the design analysis and the calibration experiments show that the deviation between the design analysis and the calibration mean value of the locking force in each case is within 10%, and the design analysis method is valid and reliable. The final tightening torque angle for clinical application is determined to be 10° and the rated torque is 2.8 N?mm. The key data obtained can be used in the design of clinical protocols and subsequent mechanical optimization of novel orthodontic devices, and the research methodology can provide a valuable reference for force analysis of medical devices containing SMA materials.
In the orthodontics process, intervention and sliding of an orthodontic bracket during the orthodontic process can arise large response of the labio-cheek soft tissue. Soft tissue damage and ulcers frequently happen at the early stage of orthodontic treatment. In the field of orthodontic medicine, qualitative analysis is always carried out through statistics of clinical cases, while quantitative explanation of bio-mechanical mechanism is lacking. For this purpose, finite element analysis of a three-dimensional labio-cheek-bracket-tooth model is conducted to quantify the bracket-induced mechanical response of the labio-cheek soft tissue, which involves complex coupling of contact nonlinearity, material nonlinearity and geometric nonlinearity. Firstly, based on the biological composition characteristics of labio-cheek, a second-order Ogden model is optimally selected to describe the adipose-like material of the labio-cheek soft tissue. Secondly, according to the characteristics of oral activity, a two-stage simulation model of bracket intervention and orthogonal sliding is established, and the key contact parameters are optimally set. Finally, the two-level analysis method of overall model and submodel is used to achieve efficient solution of high-precision strains in submodels based on the displacement boundary obtained from the overall model calculation. Calculation results with four typical tooth morphologies during orthodontic treatment show that: ① the maximum strain of soft tissue is distributed along the sharp edges of the bracket, consistent with the clinically observed profile of soft tissue deformation; ② the maximum strain of soft tissue is reduced as the teeth align, consistent with the clinical manifestation of common damage and ulcers at the beginning of orthodontic treatment and reduced patient discomfort at the end of treatment. The method in this paper can provide reference for relevant quantitative analysis studies in the field of orthodontic medical treatment at home and abroad, and further benefit to the product development analysis of new orthodontic devices.
【摘要】 目的 探討在基層醫院建立腦卒中單元模式的臨床意義。 方法 將2006年1-3月和2007年同期共381例腦卒中患者分為腦卒中單元組和普通病房組。腦卒中單元組按照腦卒中單元模式進行治療，普通病房組按照傳統方法治療，分別于治療前、治療后7、15、30 d時，對比分析兩組患者神經功能缺損及療效。 結果 腦卒中單元組和普通病房組治療后，隨時間兩組的神經功能缺損評分（NIHSS）均逐漸降低，兩組在治療后15、30 d時差異有統計學意義（P=0.007），腦卒中單元組家屬滿意度明顯高于普通病房組（P=0.002）。 結論 在基層醫院腦卒中單元模式對腦卒中患者的治療效果明顯優于傳統治療。【Abstract】 Objective To investigate the clinical significance of setting up stroke unit model in basic hospital. Methods Three hundreds and eighty-one stroke patients were randomly divided into stroke unit group (n=186) and general ward group (n=189). The stroke unit group patients were treated with the stroke unit model designed by ourselves, while the control group patients were treated with traditional method, The clinical efficacy was compared before treatment, seven days, 15 days and 30 days after treatment. Results Improvement in neurological score was significantly better among patients treated in the SU than in the GW. NIHSS scores gradually reduce in the both groups after treatment, which were significantly lower than those in the control group on 15 days and 30 days after treatment(P=0.007,0.004). The satisfactory of relatives in the stroke unit group was better than that in the general ward group(P=0.002). Conclusion The efficacy of treatment with stroke unit model was better than that of treatment with traditional method in the stroke patients.