正畸牙移动过程中龈沟液白细胞介素-8的变化

细胞因子白细胞介素-8(Interleukin-8,IL-8)被认为是重要的牙槽骨吸收调节因子,为评价正畸牙移动过程中牙周组织IL-8的水平,选择17颗需远中移动的正畸尖牙,酶联免疫吸附测定法定量分析加力前与加力后1 h、24 h、7 d、14 d及30 d龈沟液中IL-8含量的变化.结果显示:牙受力后1 h、24 h及7 d IL-8含量均较受力前显著增加(p<0.05),且在24 h达到峰值(p<0.01).表明在正畸加力初期,牙周组织IL-8含量显著增加.说明牙周组织对正畸力的生物应答反应导致IL-8增加和中性粒细胞聚集,这可能是骨改建的触发因素之一.     

牙齿矫形的三维有限元模拟分析

该文利用螺旋CT和图像数字化处理技术对活体牙齿 -齿槽骨结构进行几何重建 ,并在此基础上进行了三维实体有限元建模。对齿槽骨磨损程度不同的 3种结构进行了力学研究 ,分析了多种矫正载荷与牙齿 -齿槽骨结构位移、应力之间的关系 ,认为需要的矫正载荷与齿槽骨磨损程度有关 ,且载荷形式和作用点对矫正结果影响较大。     

A new family of primitive mammal from the Mesozoic of western Liaoning, China

A fairly well-preserved specimen of a new primitive mammal, Repenomamus robustus gen. et sp. nov., has been described from the Yixian Formation (Lower Cretaceous), western Liaoning, China. This animal has several derived characteristics, such as well-developed den-tary/squamosal articulation, reduced number of tooth, differentiation of premolars and molars in postcanine teeth, presence of a dorsal process of the premaxilla that is not in contact with the nasal, closed medial wall of the orbit, and presence of fingerlike promontorium on the petrosal. It also retains some primitive reptile-like features. It is the most primitive taxon among the three mammals known from the Jehol Biota, and also represents the largest mammal of Mesozoic age over the world.     

外伤性脱位牙保留牙髓再植术的临床研究

探讨外伤性脱位牙保留牙髓再植术的临床治疗效果。对97颗不同类型的外伤性脱位牙采用保留牙髓植术．并对治疗方法和治疗效果进行综合分析。结果表明，外伤性脱位牙保留牙髓再植术后，牙髓愈合率为34．02％，正常牙周膜愈合率为55．67％，根管治疗率为62．89％，牙根吸收率为44．33％。可见外伤性脱位牙保留牙髓再植术可获得较高的牙髓愈合率，最大限度地保留活髓，牙周膜愈合率也得到提高，从而提高了患牙的长期保存率。     

推杆针轮活齿传动的扭转刚度分析

为研究推杆针轮活齿传动的扭转刚度及其影响因素,应用变形协调方法推导了推杆针轮活齿传动的啮合力及扭转刚度的计算公式.应用实例分析了推杆针轮活齿传动的啮合力变化规律及扭转刚度变化规律,讨论了推杆针轮活齿传动的结构参数对其扭转刚度的影响.实例分析表明:推杆活齿在齿顶和齿根处所受啮合力最小,在齿廓中部受啮合力最大;推杆针轮活齿传动的扭转刚度波动较很小;激波器偏心距和针齿数对扭转刚度的影响大;针齿半径和针轮半径对扭转刚度的影响较小;激波器半径对扭转刚度的影响几乎可以忽略.研究成果可为推杆针轮活齿传动的齿廓修形和参数选择提供理论依据.      

The caries resistance of human teeth is determined by the spatial arrangement of hydroxyapatite microcrystals in the enamel

Teeth from different people differ in their susceptibility to caries. The beginning and the development of tooth decay depend on the presence of bacterial plaque and on the structure of the tooth enamel. But it has not been established whether the organic or the inorganic component of the enamel (which is comprised principally of hydroxyapatite microcrystals organized in a firm matrix), is responsible for most of the resistance of teeth to caries. We report here that the electron spin resonance (ESR) lines of the (CO3)3 defect of samples of enamel prepared from caries-resistant teeth differ significantly from the corresponding spectra of the caries-sensitive samples. We have traced these differences to the hydroxyapatite microcrystalline alignment in the tooth enamel, and found that this alignment is specific to individuals and is therefore probably nutritionally or genetically determined.     

河南鲤科鱼类咽骨咽齿的比较研究(五)

<正> 本文记述(鱼句)亚科鱼类11属20种,鲅亚科鱼类2属2种,现将对其咽骨咽齿的比较研究结果予以报导。(鱼句)亚科Gobioninae,咽骨的长宽度常有变异。体长为骨长的12.0一27.0倍,骨长为骨宽的2.5~7.0倍。前肢略长于或等于后肢。前后角圆钝或后角不明显。咽齿1~3列,内列5齿,中列2一3齿,外列1齿,各齿光滑无锯齿。     

79颗患牙采用bFGF胶原膜盖髓的临床观察

目的:探讨79例采用碱性生长因子(bFGF)的胶原蛋白膜盖髓的临床疗效,为临床寻找更有效的盖髓材料提供参考。方法:应用含有bFGF胶原蛋白膜对36颗因龋病和43颗因牙外伤而穿髓的患牙进行盖髓,分析其术后效果,同时与应用氢氧化钙对17颗因龋病和33颗因牙外伤而穿髓的患牙进行盖髓的疗效进行对比。结果:应用含bFGF胶原蛋白膜治疗外伤穿髓的盖髓效果优于氢氧化钙(P<0.05),应用含bFGF胶原蛋白膜治疗外伤穿髓的效果优于龋病治疗意外穿髓的效果(P<0.05),但含bFGF胶原蛋白膜与氢氧化钙比较,对龋病治疗意外穿髓的盖髓效果无显著性差别(P>0.05)。结论:含碱性生长因子的生物膜可以作为盖髓材料在临床应用。     

浙江鲤科鱼类咽骨咽齿的研究I

本文根据历年来所收集的鲃亚科鱼类标本,研究其咽骨咽齿的形态,阐明其异同,可供研究鲤科鱼类分类的参考.     

牙髓治疗的后牙纵折451例分析

分析牙髓治疗的后牙发生纵折的原因,并探讨预防措施。对门诊451例牙髓治疗的后牙发生牙纵折的牙齿特点和牙折情况进行检查和分析。牙髓治疗的后牙发生纵折处,有高尖陡坡或／和牙壁薄弱的牙体特征者占80．71％之多。说明高尖陡坡、薄弱牙壁是后牙纵折的重要原因,调[牙合]和冠套修复是对牙髓治疗后牙进行保护和预防纵折的重要措施。     

牙隐裂的综合治疗及疗效观察

目的 :探讨隐裂牙的治疗方法 ,评价隐裂牙综合治疗后的临床效果。方法 :对 1993年～ 1997年治疗的 85例隐裂牙进行列表统计分析 ,观察疗效。结果 :85例隐裂牙综合治疗后 ,2年以上疗效观察 ,总的牙齿保存率为 89.4% ,隐裂牙的疗效与牙髓活力、叩诊症状、牙齿松动度对照统计分析 ,都有显著性差异。结论 :对隐裂牙及时调牙合 ,均衡全口牙合力负担 ,牙髓治疗、全冠修复是保存隐裂牙十分重要的治疗措施 ,隐裂牙早发现、早治疗可提高患牙保存率。     

High-level similarity of dentitions in carnivorans and rodents

The study of mammalian evolution depends greatly on understanding the evolution of teeth and the relationship of tooth shape to diet. Links between gross tooth shape, function and diet have been proposed since antiquity, stretching from Aristotle to Cuvier, Owen and Osborn. So far, however, the possibilities for exhaustive, quantitative comparisons between greatly different tooth shapes have been limited. Cat teeth and mouse teeth, for example, are fundamentally distinct in shape and structure as a result of independent evolutionary change over tens of millions of years. There is difficulty in establishing homology between their tooth components or in summarizing their tooth shapes, yet both carnivorans and rodents possess a comparable spectrum of dietary specializations from animals to plants. Here we introduce homology-free techniques to measure the phenotypic complexity of the three-dimensional shape of tooth crowns. In our geographic information systems (GIS) analysis of 441 teeth from 81 species of carnivorans and rodents, we show that the surface complexity of tooth crowns directly reflects the foods they consume. Moreover, the absolute values of dental complexity for individual dietary classes correspond between carnivorans and rodents, illustrating a high-level similarity between overall tooth shapes despite a lack of low-level similarity of specific tooth components. These results suggest that scale-independent forces have determined the high-level dental shape in lineages that are widely divergent in size, ecology and life history. This link between diet and phenotype will be useful for inferring the ecology of extinct species and illustrates the potential of fast-throughput, high-level analysis of the phenotype.     

离散齿谐波传动啮合力及接触应力分析

对离散齿谐波传动啮合副进行力学分析,基于变形协调方程计算作用于离散齿上的力,并根据赫兹方程求解啮合副处的接触应力.由离散齿谐波传动的周期性,通过连续取波发生器的输入角值,得到离散齿谐波传动啮合力和接触应力在刚轮齿廓、波发生器和离散齿体上的分布.对刚轮齿廓出现与未出现顶切现象,得到啮合力和接触应力在接触面上的变化趋势,以及传动中出现高啮合力和高接触应力的位置,为进一步的强度校核和结构优化设计提供依据.     

On the difficulty of increasing dental complexity

One of the fascinating aspects of the history of life is the apparent increase in morphological complexity through time, a well known example being mammalian cheek tooth evolution. In contrast, experimental studies of development more readily show a decrease in complexity, again well exemplified by mammalian teeth, in which tooth crown features called cusps are frequently lost in mutant and transgenic mice. Here we report that mouse tooth complexity can be increased substantially by adjusting multiple signalling pathways simultaneously. We cultured teeth in vitro and adjusted ectodysplasin (EDA), activin A and sonic hedgehog (SHH) pathways, all of which are individually required for normal tooth development. We quantified tooth complexity using the number of cusps and a topographic measure of surface complexity. The results show that whereas activation of EDA and activin A signalling, and inhibition of SHH signalling, individually cause subtle to moderate increases in complexity, cusp number is doubled when all three pathways are adjusted in unison. Furthermore, the increase in cusp number does not result from an increase in tooth size, but from an altered primary patterning phase of development. The combination of a lack of complex mutants, the paucity of natural variants with complex phenotypes, and our results of greatly increased dental complexity using multiple pathways, suggests that an increase may be inherently different from a decrease in phenotypic complexity.     

非标准复合齿轮插齿刀设计方法

研究加工不等齿厚的非标准参数渐开线齿形,与非渐开线齿形复合的锁闭齿轮插齿刀刀齿的排列、刀具齿数的选择以及刀具设计的基本方法,介绍用限制区域选择插齿刀变位系数的新方法,并给出刀具齿顶后角与侧螺旋角的关系曲线,为插齿刀参数的选择提供依据,结果表明,采用上述方法设计非标准复合齿轮插齿刀,可简化计算和提高设计效率。     

渐开线齿轮UG参数化设计的几个关键问题

建立渐开线、齿根过渡曲线对称方程,精确计算方程参变量取值及不同建模形式的分界齿数,提供锥齿轮背锥基准平面与基准坐标系建立方法,参数化关键问题的解决保证了齿轮齿廓曲线的真实性,避免了齿廓不对称和参数丢失问题,真正实现了齿轮建模的参数化设计.     

基于计算机视觉的齿轮齿数、公法线长度变动检测

在基于计算机视觉的齿轮检测中，首次运用极坐标变换算法对预处理后的齿廓采样数据进行变换，将圆周上的齿廓曲线变换到水平方向，并将得到的齿廓看作正弦曲线，再采用Matlab工具箱中傅里叶变换函数得到正弦曲线的拟合表达式，对齿廓采样数据的总数（即列数）与拟合函数的周期比值取整，得到所检测齿轮的齿数。在检测公法线长度变动时，首先求得齿顶圆半径、模数，从而得到基圆半径，可求得基圆与齿廓交点的中点与斜率，利用点斜式方程求得与基圆相切的切线方程，该切线与跨过k个齿的齿廓相交的长度即为公法线长度，根据其最大值与最小值之差得到公法线长度变动。文中提出的基于计算机视觉系统的检测齿轮的齿数以及公法线长度的检测方法，实现了齿轮精度非接触式检测，且其检测精度能够满足工程实践的需求。     

齿间滑动摩擦对机床增速齿轮传动中大齿轮齿根弯曲疲劳强度的影响

本文作者在对机床增速齿轮传动中大齿轮受力状况作全面分析及研究基础上推导出一组公式,利用该组公式可计算机机床增速齿轮传动中大齿轮在包括齿间滑动摩擦在内的实际载荷作用下的齿根弯曲疵劳应力。     

活齿传动齿形综合的第Ⅱ类反解问题及相似变换法

本文研究活齿传动齿形综合的第Ⅱ类反解问题。综合方法采用以主从动轮理论廓线间的基本关系式为基础的相似变换法。从有利于工业化生产方面考虑,有选择地推导了渐开线等几种齿形的理论廓线及实际廓线。简略分析了几种齿形在活齿传动技术中的运用前景。     

齿轮轮齿的体应力楔弹分析法

齿轮轮齿模化楔形体在楔顶受载的弹性力学分析法,能使轮齿的体应力分析,比悬臂板、复变函数等分析法简单明瞭,比悬臂梁分析法精确全面。其分析表明轮齿体应力中的剪应力不容忽视,复合应力比悬臂梁法分析的齿体同一部位的应力要大得多,楔顶角与齿顶压力角对其应力都有一定的影响,楔顶角愈小,齿的压缩侧与拉伸侧的应力差就越小。