透明矫治器压低下前牙的生物力学分析

目的探索透明矫治器压低下前牙过程中牙齿唇舌向倾斜度的变化规律及相应的生物力学机制,获得牙齿垂直压低过程中的唇舌向控制策略。方法建立透明矫治器垂直压低下前牙的仿真模型,设计不同切牙下颌平面角度(incisor mandibular plane angle,IMPA),设置常规组、唇侧压低附件组、唇侧控根嵴组及舌侧控根嵴组,分析下前牙的位移趋势及唇舌向力矩。结果在下前牙压低中,IMPA<90°时牙冠受到舌向力矩;IMPA>90°时,牙冠受到唇向力矩。牙冠部添加唇侧控根嵴可以增加牙冠唇向转矩趋势,添加舌侧控根嵴及唇侧附件增加牙冠舌向转矩趋势。结论透明矫治器压低下前牙中会出现牙冠非设计性的唇舌向移动。牙冠唇倾时,可以设计舌侧控根嵴来避免牙冠唇向移动;牙冠舌倾时,可以设计唇侧控根嵴来避免牙冠舌向移动。

铅酸电池放电倍率对硫酸铅的性能影响

通过循环伏安和电镜扫描分析研究了铅酸电池负极放电过程中和不同放电倍率下硫酸铅的特性。高荷电态电极还原峰电位低与电极的导电性高有关,低荷电态下和高倍率放电后电极的充电接受能力高与硫酸铅周围铅离子浓度高有关。硫酸铅晶体的尺寸随放电倍率增大逐渐变小,但不呈线性关系。

不同加载频率及力值的循环张应力对大鼠颅底软骨细胞的影响

目的构建颅底软骨细胞体外培养力学模型,研究不同条件循环张应力(cyclic tensile strain, CTS)对颅底软骨细胞的影响。方法采用FX-5000T应力加载系统对体外培养的第2代大鼠颅底软骨细胞施加不同条件的循环张应力,加力大小分别为5%、10%延伸率,加力频率分别为0.3、0.5、1.0 Hz,加力时间为24 h。加力后即刻收集细胞,提取总RNA,实时荧光定量PCR检测颅底软骨细胞Ⅱ型胶原(type-Ⅱcollagen,Col-Ⅱ)和Sox9 mRNA的表达。数据采用SPSS 17.0软件包进行统计学分析。结果循环张应力大小为10%延伸率、频率为0.5 Hz或1.0 Hz时可显著促进大鼠颅底软骨细胞Col-Ⅱ及Sox9表达(P<0.05)。结论适宜条件的循环张应力可促进大鼠颅底软骨细胞基质合成。

一种环保、经济型电动自行车用电池负板合金生产工艺的研究与探讨

采用冷加工改进负板合金的生产工艺,并从降低合金铅成本,负板合金的金相、光谱数据,板栅与活性物质结合情况,电池的初期容量、低温性能、循环性能等几个方面展开研究。实验结果显示,通过改进负板合金生产工艺,电动自行车用铅酸蓄电池用铅成本大幅降低,而且电池的初期容量、低温性能、循环性能不受影响。

Effects of Mandibular Extractions with Clear Aligners:A Finite Element Analysis

This study was aimed at analysing the mechanical characteristics of different mandibular extraction modes using a clear aligner.Three experimental schemes of different extraction patterns were designed to treat mandibular crowding,including extraction of one mandibular central incisor,bilateral first premolars,and bilateral second premolars.The stress distribution during the space closing was analysed using the finite element method.When a central incisor was extracted,a significant retraction force was found in the anterior region,in line with the design expectation.The posterior teeth,which were designed to move mesially,acted as anchorage for anterior retraction,and were subjected to a mesial force.The anterior teeth were retracted when the bilateral first premolars were extracted.The lateral incisors and canines were subjected to a significant distal force and moment,while the central incisors and canines were subjected to lingual forces and moments.Additionally,the canines were subjected to a non-designated intruding force.The molars were designed to move mesially when the bilateral second premolars were extracted.All molars were subjected to a significant mesial force,while the lingual force on the front teeth was slight.The bilateral second molars were subjected to non-design mesial moment and extrusive force.The bilateral first molars were subjected to a non-designated mesial moment,and the bilateral first premolars on both sides were subjected to non-designated intrusive force and distal moment.When one incisor was extracted,attachments on the anterior teeth had a controlling effect on the tooth axis,but the anterior teeth still tended to tilt.When the bilateral first premolars were extracted,the anterior teeth showed a tendency for lingual inclination.The risk of distal inclination of the canines and lingual inclination of the central incisor increased.When the bilateral second premolars were extracted and the posterior teeth were designed to move mesially,the teeth on both sides of the extraction sites showed an obvious bowing effect.