Longitudinal analysis of deciduous tooth emergence: III. Sexual dimorphism in Bangladeshi, Guatemalan, Japanese, and Javanese children

Previous studies, mostly in European populations, found sex differences in the pattern of deciduous tooth emergence. Most studies find that the anterior dentition in males is precocial relative to the female dentition, and the pattern reverses so that females lead males in the emergence of the posterior deciduous dentition. Less is known about sex differences in the dental development and emergence of non-European populations. Here we examine the pattern of sex differences in deciduous tooth emergence in Japanese, Javanese, Guatemalan, and Bangladeshi children. The data come from four longitudinal or mixed longitudinal studies using similar study protocols. Survival analysis was used to estimate parameters of a log-normal distribution of emergence for each of the 10 teeth of the left dentition, and sexual dimorphism was assessed by sex-specific differences in mean emergence times and by Bennett's index. The results support the pattern of developmental cross-over observed in other populations. We conclude that there is little evidence to support the hypothesis of Tanguay et al. ([1984] J. Dent. Res. 63:65-68) that ethnic factors mediate sex differences in the emergence of deciduous teeth.     

Evolutionary Implications of Dental Eruption in Dasypus (Xenarthra)

Late eruption of the permanent dentition was recently proposed as a shared anatomical feature of endemic African mammals (Afrotheria), with anecdotal reports indicating that it is also present in dasypodids (armadillos). In order to clarify this question, and address the possiblity that late eruption is shared by afrotherians and dasypodids, we quantified the eruption of permanent teeth in Dasypus, focusing on growth series of D. hybridus and D. novemcinctus. This genus is the only known xenarthran that retains two functional generations of teeth. Its adult dentition typically consists of eight upper and eight lower ever-growing (or euhypsodont) molariforms, with no premaxillary teeth. All but the posterior-most tooth are replaced, consistent with the identification of a single molar locus in each series. Comparison of dental replacement and skull metrics reveals that most specimens reach adult size with none or few erupted permanent teeth. This pattern of growth occurring prior to the full eruption of the dentition is similar to that observed in most afrotherians. The condition observed in Dasypus and many afrotherians differs from that of most other mammals, in which the permanent dentition erupts during (not after) growth, and is complete at or near the attainment of sexual maturity and adult body size. The suture closure sequence of basicranial and postcranial epiphyses does not correlate well with dental eruption. The basal phylogenetic position of the taxon within dasypodids suggests that diphyodonty and late dental replacement represent the condition of early xenarthrans. Additionally, the inferred reduction in the number of molars to a single locus and the multiplication of premolars represent rare features for any living mammal, but may represent apomorphic characters for Dasypus.     

The dentition of New Britain West Nakanai Melanesians. VIII. Peopling of the pacific

The dental crown morphology and size of 48 male West Nakanai, New Britain, Melanesians is described and compared with other Pacific and Asian dental samples. The West Nakanai dentition is like those of other Melanesians, much less like those of Polynesians and Micronesians, and very dissimilar to teeth of modern and Neolithic Southeast Asians. It is suggested that the origin of the modern Melanesian dental pattern (large but simplified teeth) was probably in Melanesia, not Southeast Asia as the orthodox view of a Hoabinhian-Australmelanesian relation claims.     

Functional relationships between dental attrition and the helicoidal plane

Several quantitative techniques were used to describe and analyze the development of the helicoidal curve of the dentition in a pre-contact sample of 326 native Indians from British Columbia. Results were compared with studies of occlusal patterns in other populations, and anatomical-functional features of the helicoidal pattern were abstracted and generalized. The features that define the helicoidal pattern were found to develop with attrition. The pattern itself, and the complex which produces it, probably have been selected for because they produce an occlusion with an efficient cutting edge and a total complex that provides maximum resistance to the masticatory forces. Studies focusing on the developmental nature of occlusal patterns in early hominid populations would be beneficial in developing a model of the evolution of the helicoidal pattern in modern man.     

长阳青铜时代与大同北魏朝代人类牙齿的形态变异

本文记述了湖北长阳县深潭湾青铜时代和山西大同市郊北魏朝代两处墓葬遗址出土的人类牙齿形态变异的状况,提供人们对牙齿形态种种变异的认识,探索非测量性牙齿特征在研究种族和人群之间关系中的意义。     

Study of dentition in lizards from Gran Ganaria Island (Canary Islands) and its ecological and evolutionary significance

The dentition of Gallotia stehlini from one extant and two subfossil populations dated as 4000 and 2000 years before present was studied. Body measurements were similar in the two subfossil populations, but much greater than the largest sizes observed today in G. stehlini. The morphology of the dental cusps in this G. stehlini differs greatly from that of other Lacertidae, including other congeneric Canarian species; this has been connected with a vegetarian diet. A decrease in heterodonty with size of the animal is also seen which contrasts strongly with the models observed in the Mediterranean lacertid lizards.     

Dental modifications and tool use in the western Great Basin

Nondietary function is an important concern in the study of the human dentition and its role in adaptation. The purpose of the present investigation is to describe and interpret a pattern of dental wear in the anterior dentition of precontact hunter-gatherers that inhabited the western Great Basin. These data are discussed in light of ethnographic documentation as a means by which the archaeological record is linked with associated behavior of the representative populations. A series of 171 dentitions from a group of archaeological localities was examined. Of 1,931 teeth observed, 16 of these showed narrow (0.4-2.0 mm) transverse grooves located on the midocclusal surfaces of anterior teeth. The grooves were restricted in occurrence to five older adult males. Documentation of prehistoric and historic western Great Basin aboriginal populations indicates an adaptation that involves use of plant materials in the production of a variety of utilitarian objects, such as fish nets, basketry, funerary bags, fowling bags, and rope. In postcontact contexts, the anterior dentition has been shown to play an important role in the preparation of materials used for the production of this equipment. It seems most likely, then, that the grooves observed herein resulted directly from the use of the dentition as part of the tool assemblage for the production of other tools.     

Tooth Size Variation in Prehistoric India

Permanent dental crown dimensions are largely unknown for living and prehistoric populations of South Asia. This paper describes permanent tooth crown measurements and indices for the Late Chalcolithic skeletal series from Inamgaon (1700-700 B.C.) in western India. These data are compared with tooth size data for prehistoric populations in India and both living and prehistoric populations outside the South Asian subcontinent. In summed cross-sectional area, the Inamgaon (1,218 mm²) permanent teeth are most similar to prehistoric skeletal series from Mahurjhari, India, Non Nok Tha, Thailand, and Bellan Bandi Palassa, Sri Lanka. The Inamgaon total crown area is only 3.1% smaller than the figure reported for early Neolithic skeletons from Mehr-garh, Pakistan, indicating the relatively large size of the Inamgaon dentition. Large tooth size at Inamgaon is interpreted as a biological adaptation to coarse dietary items, basic food preparation methods, and a mixed economy that included hunting wild game and collecting wild fruit. Dental indices of "ethnic" significance are perhaps better interpreted as indicators of masticatory stress and differential dental reduction. Maxillary and mandibular third molars show minimal reduction in crown size, but mandibular second molar teeth are distinctly reduced in size. The Incisor Breadth Index may indicate mixed genetic ancestry of the Inamgaon people or similar dietary stresses in genetically different populations.     

Deciduous dentition and eruption pattern in late Miocene Pachyrukhinae (Hegetotheriidae,Notoungulata) from La Pampa Province,Argentina

The study of juvenile remains of Paedotherium Burmeister from Cerro Azul Formation (La Pampa Province, Argentina; late Miocene) is presented. Upper and lower deciduous dentition (or permanent molars supposed to be associated with non-preserved deciduous teeth) are recognised. Several ontogenetic stages are distinguished among juveniles, according to the degree of wear and the replaced deciduous teeth. Besides, some morphological and metrical differences are observed along the crown height. Deciduous cheek teeth are high-crowned and placed covering the apex of the corresponding permanent tooth. The height of the crown and the degree of wear allow establishing the pattern of dental replacement of deciduous and permanent premolars in a posterior–anterior direction (DP/dp4–2 and P/p4–2), as well as the eruption of M/m3 before DP/dp4 is replaced. Some of the studied remains are recognised as young individuals of Tremacyllus Ameghino, but with complete permanent dentition, which leads to propose a different timing in the dental replacement with respect to Paedotherium; they also allow the establishment of an opposite premolar eruption pattern, from P/p2 to P/p4. This knowledge of the deciduous dentition of Paedotherium suggests the need of revising the morphological and metrical characters previously used for defining species within this taxon.     

Whole-body imaging of the distribution of mercury released from dental fillings into monkey tissues

The fate of mercury (Hg) released from dental "silver" amalgam tooth fillings into human mouth air is uncertain. A previous report about sheep revealed uptake routes and distribution of amalgam Hg among body tissues. The present investigation demonstrates the bodily distribution of amalgam Hg in a monkey whose dentition, diet, feeding regimen, and chewing pattern closely resemble those of humans. When amalgam fillings, which normally contain 50% Hg, are made with a tracer of radioactive 203Hg and then placed into monkey teeth, the isotope appears in high concentration in various organs and tissues within 4 wk. Whole-body images of the monkey revealed that the highest levels of Hg were located in the kidney, gastrointestinal tract, and jaw. The dental profession's advocacy of silver amalgam as a stable tooth restorative material is not supported by these findings.     

Patterns of tooth crown size and shape variation in great apes and humans and species recognition in the hominid fossil record

It has been suggested that patterns of craniodental variation in living hominids (Gorilla, Homo, Pan, and Pongo) may be useful for evaluating variation in fossil hominid assemblages. Using this approach, a fossil sample exhibiting a pattern of variation that deviates from one shared among living taxa would be regarded as taxonomically heterogeneous. Here we examine patterns of tooth crown size and shape variation in great apes and humans to determine 1) if these taxa share a pattern of dental variation, and 2) if such a pattern can reliably discriminate between samples that contain single species and those that contain multiple species. We use parametric and nonparametric correlation methods to establish the degree of pattern similarity among taxa, and randomization tests to assess their statistical significance. The results of this study show that extant hominids do not share a pattern of dental size variation, and thus these taxa cannot be used to generate expectations for patterns of size variation in fossil hominid species. The hominines (Gorilla, Homo, and Pan) do share a pattern of shape variation in the mandibular dentition; however, Pongo is distinct, and thus it is unclear which, if either, pattern should be expected in fossil hominids. Moreover, in this case, most combined-species samples exhibit patterns of shape variation that are similar to those for single hominine species samples. Thus, although a common pattern of shape variation is present in the mandibular dentition, it is not useful for recognizing taxonomically mixed paleontological samples.     

Evolution of the dentition in prehistoric Ohio Valley Native Americans: II. morphology of the deciduous dentition

In order to evaluate the microevolutionary dynamics of morphological features of the deciduous dentition, I collected data on the variation of 57 features (33 crown and 24 root) from prehistoric Ohio Valley populations. I sampled a total of 370 individuals from 26 populations representing a lineage that inhabited the middle and upper Ohio valley region from approximately 3000 to 350 BP. Evolutionary changes in the frequencies of morphological features of the deciduous teeth in this lineage were limited. Over 80% of the features show no significant differences among the populations. The relatively few features that show consistent differences separate pre- and postmaize agricultural populations. I discuss explanations for this change in terms of selection differences or gene flow. The general pattern of morphological trait expression in the deciduous teeth of this Ohio Valley lineage corresponds to what has been termed the Mongoloid dental complex (sinodonty in the permanent teeth). I suggest additional features that, with further study, may be added to this morphological complex. Am J Phys Anthropol 106:189–205, 1998. © 1998 Wiley-Liss, Inc.     

Pan paniscus and human evolution

Detailed comparisons of the postcranium, cranium, and dentition of Pan paniscus, Pan troglodytes, and Homo reveal that except for slight differences in fore- and hindlimb proportions and the morphology of the shoulder, the postcranium of the two species of Pan are allometrically scaled variants of the same animal and one does not resemble Homo more than the other. Nor does the postcranium of one species of Pan resemble Australopithecus more closely than the other when the effects of body size are controlled. The over all morphological pattern of the skull and teeth of the two chimpanzees is clearly different, however, but both are about equally distinct from the earliest known members of the family Hominidae.     

Study on some genetic traits of Tibetans at Chandragiri, District Ganjam, Orissa

The incidence of ABH secretion, dry cerumen, ear-lobe attachment, hand clasping, arm-folding, and digital hair, occipital hair whorl and relative length of first and second toes is reported for Tibetan refugees. In those traits for which comparative data are available, they resemble Mongoloid rather than Caucasoid populations.     

秦岭野生大熊猫牙齿的形态机能

大熊猫(Ailuropoda melanoleuca)是国家一级保护动物,被誉为国宝.牙齿作为大熊猫消化器官之一,相对于其他动物而言,大熊猫牙齿有其自身的构造特点.以往学者和专家对大熊猫牙齿形态的研究侧重于为大熊猫的种群分类寻找根据(Dvadi,1869; Milne-Edwards,1870;王将克,1974),更多关注牙齿在大熊猫进化、演变过程中的意义(王令红等,1982;黄万波,1993).研究的齿位大多局限于臼齿(张鹤宇和刘理,1959),所得结果或数据并不详细和全面.此外,还有一些学者对大熊猫牙齿釉质的超微组织结构进行研究(赵资奎等,1984 ).     

金丝猴牙齿与体重间的相关性研究

对金丝猴牙齿与体重间关系的研究结果表明,在雄性中,无论是线性还是面积与颅长之间的相关关系均较雌性的更为紧密。而且,随着体重的增加,雄性牙齿的近中远中长(M/D)也比雌性的增长较快。在上、下颌中,上颌牙齿与颅长的关系表现出更强的相联性。与其他灵长类相比较,金丝猴在取食和咀嚼过程中主要利用颊齿;大的个体具有大的犬齿及一定比例的臼齿面积和齿弓(牙合)面面积;上齿弓(牙合)面面积大于下齿弓(牙合)面面积。也就是说上齿弓提供了比下齿弓更大的咀嚼面积。金丝猴牙齿与体重间的关系位于猴类和人猿类之间,更接近于大猩猩(Gorilla)、疣猴(Colobus)和猕猴。     

Unique pattern of dietary adaptation in the dentition of Carnivora: its advantage and developmental origin

Carnivora is a successful taxon in terms of dietary diversity. We investigated the dietary adaptations of carnivoran dentition and the developmental background of their dental diversity, which may have contributed to the success of the lineage. A developmental model was tested and extended to explain the unique variability and exceptional phenotypes observed in carnivoran dentition. Carnivorous mammalian orders exhibited two distinct patterns of dietary adaptation in molars and only Carnivora evolved novel variability, exhibiting a high correlation between relative molar size and the shape of the first molar. Studies of Bmp7-hetero-deficient mice, which may exhibit lower Bmp7 expression, suggested that Bmp7 has pleiotropic effects on these two dental traits. Its effects are consistent with the pattern of dietary adaptation observed in Carnivora, but not that observed in other carnivorous mammals. A molecular evolutionary analysis revealed that Bmp7 sequence evolved by natural selection during ursid evolution, suggesting that it plays an evolutionary role in the variation of carnivoran dentition. Using mouse experiments and a molecular evolutionary analysis, we extrapolated the causal mechanism of the hitherto enigmatic ursid dentition (larger M₂ than M₁ and M₃). Our results demonstrate how carnivorans acquired novel dental variability that benefits their dietary divergence.     

Negritos, Australian aborigines, and the "proto-sundadont" dental pattern: the basic populations in east Asia, V.

Five evolutionarily significant dental traits were identified from a B-square distance analysis of nine crown characters recorded for several populations of East Asia and Oceania. Intergroup variation in these traits distinguishes three major divisions of the Mongoloid dental complex: sundadonty, sinodonty, and the dental pattern of Australian Aborigines. The Australian crown features may be characterized as having high frequencies of evolutionarily conservative characters. Negritos, one of the probable representatives of indigenous inhabitants of Southeast Asia who may have shared a common ancestor with Australians, possess the more derived sundadont dental pattern. As far as the five crown traits treated here are concerned, Australian dental features may be described as conforming to a "proto-sundadont" dental pattern, applying Turner's terminology. This pattern may represent a microevolutionary step prior to the emergence of the sundadont and sinodont patterns.     

Dental Variation in Sibling Species <Emphasis Type="Italic">Microtus arvalis</Emphasis> and <Emphasis Type="Italic">M. rossiaemeridionalis</Emphasis> (Arvicolinae,Rodentia): Between-Species Comparisons and Geography of Morphotype Dental Patterns

The data on dental variability in natural populations of sibling species of common voles (“arvalis” group, genus Microtus) from European and Asian parts of the species’ ranges are summarized using a morphotype-based approach to analysis of dentition. Frequency distributions of the first lower (m1) and the third upper (M3) molar morphotypes are analyzed in about 65 samples of M. rossiaemeridionalis and M. arvalis represented by arvalis and obscurus karyotypic forms. Because of extreme similarity of morphotype dental patterns in the taxa studied, it is impossible to use molar morphotype frequencies for species identification. However, a morphotype-based approach to analysis of dental variability does allow analysis of inter-species comparisons from an evolutionary standpoint. Three patterns of dental complexity are established in the taxa studied: simple, basic (the most typical within the ranges of both species), and complex. In M. rossiaemeridionalis and in M. arvalis obscurus only the basic pattern of dentition occurs. In M. arvalis arvalis, both simple and basic dental patterns are found. Analysis of association of morphotype dental patterns with geographical and environmental variables reveals an increase in the number of complex molars with longitude and latitude: in M. arvalis the pattern of molar complication is more strongly related to longitude, and in M. rossiaemeridionalis—to latitude. Significant decrease in incidence of simple molars with climate continentality and increasing aridity is found in M. arvalis. The simple pattern of dentition is found in M. arvalis arvalis in Spain, along the Atlantic coast of France and on islands thereabout, in northeastern Germany and Kirov region in European Russia. Hypotheses to explain the distribution of populations with different dental patterns within the range of M. arvalis sensu stricto are discussed.