Developmental biology. Lungfish dental pattern conserved for 360 Myr

Lungfish, the closest living relatives of four-limbed animals, are unique in that adults lack marginal teeth and have to rely on palatal dental plates for crushing food. We have discovered that an identical pattern of tooth development is used to shape these plates in the hatchlings of fossil and living lungfish species that are separated by 360 million years (Myr) of evolution, even though the adults have very different dental forms; the same pattern is also evident in the transient marginal dentition, despite being functional only until the juvenile stage. This remarkable finding indicates that developmental programming for dentition in lungfish is uniform, unique and conserved for all tooth fields.     

Statistical analyses of metric data of hominoid teeth found in Yuanmou of China

Mesial-distal and buccal-lingual dimensions of 1 266 hominoid teeth found in Yuanmou of Yunnan Province during the period of 1986 and 1988 have been measured. The statistical analyses of the metric data show that the tooth sizes of Yuanmou hominoid can be divided into big and small two types, and most tooth dimensions display obvious bimodalities in both histograms and 2 dimensional plots. The coefficients of variance (CV) reveal that the CVs of Yuanmou hominoid tooth sizes are within or close to the CV ranges ofLufengpithecus and extant great apes. The comparisons of tooth sizes and their proportions indicate that Yuanmou hominoids have close affinities with Lefeng and Kaiyuan hominoids, and have obvious differences with Gorilla, Chimpanzee and Orangutan. The authors believe that the hominoid fossils found in Yuanmou in the past 10 years represent a single species with highly sexual dimorphism in morphology and this species may have a close evolutionary relationship with the hominoids found in Kaiyuan and Lufeng.     

Dyract AP复合体和流体树脂联合充填后牙窝洞的效果观察

目的：观察Dyarct AP复合体和流体树脂联合充填后牙窝洞的临床效果。方法：选择口腔门诊450个后牙验面洞、邻验面洞，连续观察5a，评价其临床效果。结果：la复查，100％~j填物临床效果优；2a复查，临床效果优者443牙，占98．44％；3a复查，临床效果优者434牙，占96．44％；5a复查，临床效果优者418牙．占92．89％。结论：Dyraet AP复合体和流体树脂联合充填后牙窝洞的临床效果满意。     

基于ANSYS的减速机齿轮有限元分析

采用有限元法研究齿轮轮齿在受到不同载荷的情况下,其齿根弯曲应力和应变的变化情况。结果表明,在静载荷的作用下,齿轮齿根处的最大弯曲应力和最大应变都在许可的范围之内;而当齿轮受到冲击,在动载荷作用下,齿根处的应力大于齿轮材料的屈服极限。结合对断齿形貌的分析,可推断出轮齿的断裂是在出现疲劳裂纹后受冲击载荷作用而产生的过载断裂。     

倾斜式双滚子包络环面蜗杆传动几何特性分析

为消除环面蜗杆传动齿侧间隙,提出倾斜式双滚子包络环面蜗杆传动,采取双排滚子错位布置,且滚子轴线与蜗轮径向倾斜一定角度. 阐述了倾斜式双滚子包络环面蜗杆传动的工作原理,依据空间齿轮啮合理论和微分几何理论,采用运动学法建立了蜗杆副的静态坐标系及活动坐标系,推导了该新型环面蜗杆齿面方程,并导出了该传动的蜗杆轴向截面齿廓方程、法向截面齿廓方程、一界函数、螺旋升角等几何特性相关的方程及计算公式,分析了滚柱半径R、滚柱偏距c₂、倾斜角γ等啮合参数对蜗杆几何特性的影响. 结果表明:该新型传动蜗杆喉部齿廓非常接近直线,蜗杆不会发生根切和齿顶变尖现象. 要使该传动保持良好的几何特性,R不宜超过12 mm,c₂在5~9 mm之间,γ在18°~25°之间.      

双圆弧齿轮齿腰应力的研究

本文用回归分析法求得了ＧＢ１２７５９—９１型双圆弧齿轮的齿腰应力的计算公式。研究表明，大螺旋角或小载荷时，齿腰应力大于齿根应力。因此，齿腰是一个薄弱环节，应受到重视。     

考虑温度效应的风电增速箱动力学特性研究

针对风电增速齿轮箱温度异常现象,基于Block闪温理论与Hertz接触理论,提出一种考虑随机风载作用下齿面接触温度的计算方法.以该方法为理论基础,根据行星轮系耦合建模理论,建立风电增速齿轮箱动力学性能计算模型.模型不仅揭示了随机风载、齿面接触温度及齿廓热变形之间相互影响的函数关系,还展现了随机风载、齿面接触温度等非线性...     

电脑散热片换热过程数值模拟分析

研究的对象是直板式铝散热片,通过改变散热片的结构参数(齿厚、齿高、齿间距和底板厚度),以Ansys软件为载体,将所作模型图导入Ansys软件中进行模拟,得出测试点温度.基于正交试验分析,得出结果:散热片的齿厚和齿间距对其散热效果影响最大,其次是齿高,底板厚度次之;其他参数不变时,齿厚在0.5～1.5 mm内,随着齿厚的增加,散热效果增强,齿厚超过1.5 mm,散热效果则减弱;齿间距在1～1.5 mm内,随着齿间距的增加,散热效果增强,齿间距超过1.5 mm,散热效果则减弱;随着齿高的增加,散热效果呈现增强趋势;底板厚度在2～3 mm内,随着厚度的增加散热效果增强,当厚度超过3 mm时,散热效果呈下降趋势.     

荧光分析法研究偶联剂与牙体组织的联结机理

为了进一步探讨牙体组织与粘接剂的粘接机理，我们研制了具有荧光的粘接偶联剂CGE（N）－1，用固体荧光分析方法对CGE（N）－1，牙体组织，及CGE（N）－1丙酮溶液处理后的牙体组织进行了分析测试。结果表明：用偶联剂处理后的牙面其荧光光普与未处理的相比发生了明显的红移；说明偶联剂同牙体组织之间发生了化学结合，溶液中的测试结果也证明了上述结论。     

海南文昌乡村汉族成人体型特征的研究

运用Heath-Carter体型法对海南文昌乡村汉族成人407例(男性216例,女性191例)进行体型评定.结果显示:(1)海南乡村汉族的平均体型中,男性为偏内胚的中胚层体型(4.3-4.9-2.4),女性为偏中胚层的内胚层体型(5.4-4.4-2.2);(2)随年龄的增长,男性20~40岁之间,内、中因子值升高,外因子值降低.40岁以后,有内、中因子值降低和外因子值升高的趋势.女性60岁之前,内、中因子值呈上升而外因子值下降的趋势;(3)60岁之前,男、女间体型之间的差异有统计学意义,60岁以后无差异;(4)与其他乡村族群比较,海南乡村汉族男性的平均体型点与蒙古族最接近,女性与达斡尔族最为接近;(5)海南汉族的体型具有北方族群的特征.     

球面二次包络弧面蜗杆传动的理论研究

在避免蜗杆“根切”和“变尖”的条件下,减小蜗杆的喉径,提高蜗轮付的啮合效率及蜗轮轮齿强度,改善其结构的不合理性,已成为当前对“多头小速比”包络弧面蜗杆传动啮合原理研究的重要课题。本文对一种新型包络弧面蜗杆传动——“球面二次包络弧面蜗杆传动”进行了系统的理论研究,所得的结论表明,采用该传动对解决上述问题可以获得十分令人满意的结果。     

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.     

佤族成人Heath-Carter法体型研究

运用Heath-Carter人体测量方法对云南省耿马傣族佤族自治县佤族442例成年人（男为258例,女为184例）进行了体型调查．结果表明：（1）佤族成人男女的平均体型值分别为2．2-5．5-2．5和4．0-5．0-1．9,佤族成人男女体型分别属均衡的中胚层体型和偏内胚层的中胚层体型．（2）佤族男性20-、30-和40-岁组的内因子值相同,而50-岁组的内因子值下降;中因子值和外因子值在20-岁组到40-岁组变化不明显,50岁组中因子值下降,外因子值升高,女性4个年龄组中的内、中、外因子值变化不明显．（3）佤族成人男女间的体型比较有极显著性差异（P〈0．01）．（4）与国内外其他民族相比,佤族体型与广西布依族和云南克木人最为接近．     

双圆弧齿轮瞬时接触区的简化计算

利用弹性力学原理,计算了GB12759－91型双圆弧齿轮在齿面任一点受集中力时齿面各处的下陷量,再由一对轮啮合时的空间几何关系计算出变形前齿面各点沿法向的间隙量,然后按变形直辖市关系算得当一对轮齿法向靠拢时的接触边界形状和接触区的内载荷分布。     

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。     

The oldest articulated chondrichthyan from the Early Devonian period

Chondrichthyans (including living sharks, skates, rays and chimaeras) have a fossil record of scales and dermal denticles perhaps dating back to the Late Ordovician period, about 455 million years ago. Their fossil tooth record extends to the earliest Devonian period, almost 418 million years ago, whereas the oldest known articulated shark remains date from the Early Devonian period, about 394 million years ago. Here we report the discovery of an articulated shark that is almost 409 million years old from the Early Devonian (early Emsian) period of New Brunswick, Canada. The specimen, identified as Doliodus problematicus (Woodward), sheds light on the earliest chondrichthyans and their interrelationships with basal jawed vertebrates. This species has been truly problematic. Previously known only from isolated teeth, it has been identified as an acanthodian and a chondrichthyan. This specimen is the oldest shark showing the tooth families in situ, and preserves one of the oldest chondrichthyan braincases. More notably, it shows the presence of paired pectoral fin-spines, previously unknown in cartilaginous fishes.     

仫佬族成人Heath-Carter法体型研究

运用Heath-Carter人体测量体型方法对广西罗城仫佬族自治县四把镇大梧村仫佬族成年人465例（男为232例,女为233例）进行了体型评定.结果表明：（1）仫佬族成人男女的平均体型值分别为2.4-4.5-2.8和4.1-4.0-2.2,仫佬族成人男女分别属均衡的中胚层体型和内胚层-中胚层均衡体型.（2）随年龄增长,男性内因子值在20-岁组到40-岁组缓慢增长,50-岁后增长较快,中因子值和外因子值在20岁到30岁变化明显,30岁后变化不大;女性在20-岁组到40-岁组内因子值与中因子值增长较快,外因子值逐渐减小,40岁后3因子变化不大.（3）仫佬族成人男女间的体型有极显著性差异（P〈0.01）.（4）与国内、外资料相比,仫佬族体型与宁夏回族、广西三江侗族最为接近.     

Function of the mandibular tooth comb in living and extinct mammals

Among the most interesting mammalian dental specialization is the mandibular 'tooth comb' or 'tooth scraper' that evolved independently in certain primates and other mammals. Its occurrence is most widely known in lemurs and lorises, where it is comprised of the long, slender, procumbent incisors (one or two pairs) and incisiform canines (Fig. 1). In non-primates to canines are not incorporated into the comb. Some tree shrews (Tupaiidae) possess a tooth comb consisting of the four central incisors, and some early Tertiary arctocyonid condylarths had a similar structure composed of all six lower incisors. The extant flying lemurs (Dermoptera: Cynocephalus) also have a dental 'comb' but it is very different from the ones already mentioned, consisting of two pairs of pectinate incisors, each tooth modified into a comb with as many as 15 tines. This condition, although sometimes said to be similar to that in lemurs, is unique to Cynocephalus. One of the principal functions of the tooth comb in primates is to comb the fur, and we present here indirect evidence that condylarths used this structure in the same way, millions of years before tooth combs evolved in prosimians. We also show that the comb-like incisors of Cynocephalus, contrary to popular belief, probably do not function to comb the fur.     

How Neanderthal molar teeth grew

Growth and development are both fundamental components of demographic structure and life history strategy. Together with information about developmental timing they ultimately contribute to a better understanding of Neanderthal extinction. Primate molar tooth development tracks the pace of life history evolution most closely, and tooth histology reveals a record of birth as well as the timing of crown and root growth. High-resolution micro-computed tomography now allows us to image complex structures and uncover subtle differences in adult tooth morphology that are determined early in embryonic development. Here we show that the timing of molar crown and root completion in Neanderthals matches those known for modern humans but that a more complex enamel-dentine junction morphology and a late peak in root extension rate sets them apart. Previous predictions about Neanderthal growth, based only on anterior tooth surfaces, were necessarily speculative. These data are the first on internal molar microstructure; they firmly place key Neanderthal life history variables within those known for modern humans.     

成年人形态体质指标变化的年龄特征——中国成年人体质变化的年龄特征研究之一

取2000年全国国民体质监测20．59岁成年人(计151，656个样本)相关指标数据，用曲线拟合的方法，找出主要指标变化的峰值年龄和指标变化的速率。主要结论有：成年男子体丰度在45．49岁左右，女子在55．59岁左右，均发生了较大的转折变化。