Homologies of the anterior teeth in indriidae

Schwartz ('74) proposed revised homologies of the deciduous and permanent anterior teeth in living lemuriform primates of the family Indriidae. Gingerich ('77) described a juvenile specimen of Avahi and emphasized the importance of functional integrity in controlling the pattern of dental reduction in primates, neither of which supports Schwartz's interpretation. Schwartz ('78) recently reiterated his position without adequately discussing the Avahi evidence and the functional basis that probably controls dental reduction. Avahi has a deciduous dentition intermediate in morphology between that of Lemuridae and Indriidae, and similar to both. Thus the lower deciduous dental formula of Indriidae is probably 2.1.3, which is the typical and maximum deciduous complement known in living and fossil lemuriform primates. The formula of the lower permanent dentition in Indriidae is thus 2.0.2.3.     

Homologies of the anterior teeth in Indriidae and a functional basis for dental reduction in primates

In a recent paper Schwartz ('74) proposes revised homologies of the deciduous and permanent teeth in living lemuriform primates of the family Indriidae. However, new evidence provided by the deciduous dentition ofAvahi suggests that the traditional interpretations are correct, specifically: (1) the lateral teeth in the dental scraper of Indriidae are homologous with the incisors of Lemuridae and Lorisidae, not the canines; (2) the dental formula for the lower deciduous teeth of indriids is 2.1.3; (3) the dental formula for the lower permanent teeth of indriids is 2.0.2.3; and (4) decrease in number of incisors during primate evolution was usually in the sequence I3, then I2, then I1. It appears that dental reduction during primate evolution occurred at the ends of integrated incisor and cheek tooth units to minimize disruption of their functional integrity.     

Developmental origins and homologies of the hyracoid dentition

Understanding the origins of morphological specializations in mammals is a key goal in evolutionary biology. It can be accomplished by studying dental homology, which is at the core of most evolutionary and developmental studies. Here, we focused on the evolution and development of the specialized dentition of hyraxes for which dental homologies have long been debated, and could have implications on early placental evolution. Specifically, we analysed dental mineralization sequences of the three living genera of hyraxes and 17 fossil species using X‐ray computed microtomography. Our results point out the labile position of vestigial upper teeth on jaw bones in extant species, associated with the frequently unusual premolar shape of deciduous canines over 50 Ma of hyracoid evolution. We proposed two evolutionary and developmental hypotheses to explain these original hyracoid dental characteristics. (a) The presence of a vestigial teeth on the maxilla in front of a complex deciduous canine could be interpreted as extra‐teeth reminiscent of early placental evolution or sirenians, an order phylogenetically close to hyracoids and showing five premolars. (b) These vestigial teeth could also correspond to third incisors with a position unusually shifted on the maxilla, which could be explained by the dual developmental origin of these most posterior incisors and their degenerated condition. This integrative study allows discussion on the current evolutionary and developmental paradigms associated with the mammalian dentition. It also highlights the importance of nonmodel species to understand dental homologies.     

Ontogeny and homology of the dentition in dasyurid marsupials: Development inSminthopsis virginiae

Histological analysis of an ontogenetic series of the dasyurid marsupial,Sminthopsis virginiae, from birt to 60 days old, was undertaken to assess the developmental homologies of the deciduous and successional teeth. This period covers the time from the initiation of all teeth as epithelial buds up until the time of early eruption of some teeth. In addition, two older specimens, aged 81 and 97 days, were examined to provide additional information on the state of differentiation of the unerupted third premolar. In the postcanine dentition, only a single tooth position, dP3, was characterized by the later development of a replacing successional tooth (P3), following developmental pathways identical to those in eutherian mammals. In contrast, the anterior dentition is characterized by the formation of rudimentary, nonerupting deciduous incisors and canines, and by the accelerated development of normal, erupting successional incisors and canines in both jaws. Comparison of relative developmental stages for each tooth position throughout its preeruptive ontogeny suggests thatheterochrony (both developmental acceleration and retardation) has played an important role in the evolutionary history of the dasyurid dentition. Differing aspects of this phenomenon are identified and discussed for the anterior dentition, the anterior two premolars, P3, and the lower molars. Further evidence is presented to corroborate the identification of the anterior two premolars in the adult as dP1 and dP2, based on the relative retardation of their initiation and their lack of successor tooth germs. This developmental heterochrony has probably occurred in all three-premolared marsupials.     

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.     

The study of animal bones from archaeological sites. By Raymond E. Chaplin. ix + 170 pp., figures,tables, bibliography,index. Seminar press,London. 1971. $5.75 (cloth)

A review of the literature reveals a long history of disagreement on the interpretation of the lower deciduous and permanent dentition of the Indriidae. This disagreement has centered on the existence and/or replacement of a canine as a member of the indriid toothcomb. The presence of a pair of canines in the toothcomb of lemurids and lorisids has rarely been questioned, and there is no evidence to indicate that this interpretation is incorrect. There has, however, been no consistency nor substantiating evidence presented for any interpretation of the indriid toothcomb. By comparing the morphology of the teeth of the lemurid, lorisid, and indriid toothcomb, both deciduous and permanent, comparing the mode of dental development in these three families, identifying the indriid lower deciduous dentition, and by relating the data to an ontogenetic and phylogenetic framework, this study proposes: (1) in all three families, the lateral teeth of the toothcomb are canines, (2) the dental formula for the lower deciduous teeth of indriids is 1.1.4, (3) the dental formula for the lower permanent teeth of indriids is 1.1.2.3, and (4) that decrease in number of incisors during primate evolution was most likely I1 to I2 to I3.     

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.     

Numeric anomalies of teeth in concomitant hypodontia and hyperdontia

Variations in tooth number in children, each of whom had supernumerary teeth and agenesis of teeth, is described. Among the 11, seven had cleft lip and palate, and two had clefting syndromes; two children had dental anomalies only. Only children who had both supernumerary teeth and congenitally missing teeth outside the area of the cleft alveolus were included. Concomitant hypodontia and hyperdontia were observed in the same dentition in nine subjects, in the same jaw in eight subjects, and in the same jaw quadrant in only three subjects. Supernumerary teeth and agenesis of teeth were observed simultaneously more often in the permanent dentitions than in the deciduous dentitions or in both dentitions simultaneously. The overall number of supernumeraries was 10 in the deciduous dentition and 14 in the permanent dentition of the 11 subjects. The number of congenitally absent teeth was 14 in the deciduous dentition and 40 in the permanent dentition. The etiology of concomitant hypodontia and hyperdontia is difficult to explain. It may result from disturbances in migration, proliferation, and differentiation of neural crest cells or interactions between the epithelial and mesenchymal cells during the initiation of odontogenesis.     

Changes in the Distribution of Periodontal Nerve Fibers during Dentition Transition in the Cat

The periodontal ligament has a rich sensory nerve supply which originates from the trigeminal ganglion and trigeminal mesencephalic nucleus. Although various types of mechanoreceptors have been reported in the periodontal ligament, the Ruffini ending is an essential one. It is unknown whether the distribution of periodontal nerve fibers in deciduous teeth is identical to that in permanent teeth or not. Moreover, morphological changes in the distribution of periodontal nerve fibers during resorption of deciduous teeth and eruption of successional permanent teeth in diphyodont animals have not been reported in detail. Therefore, in this study, we examined changes in the distribution of periodontal nerve fibers in the cat during changes in dentition (i.e., deciduous, mixed and permanent dentition) by immunohistochemistry of protein gene product 9.5. During deciduous dentition, periodontal nerve fibers were concentrated at the apical portion, and sparsely distributed in the periodontal ligament of deciduous molars. During mixed dentition, the periodontal nerve fibers of deciduous molars showed degenerative profiles during resorption. In permanent dentition, the periodontal nerve fibers of permanent premolars, the successors of deciduous molars, increased in number. Similar to permanent premolars, the periodontal nerve fibers of permanent molars, having no predecessors, increased in number, and were densely present in the apical portion. The present results indicate that the distribution of periodontal nerve fibers in deciduous dentition is almost identical to that in permanent dentition although the number of periodontal nerve fibers in deciduous dentition was low. The sparse distribution of periodontal nerve fibers in deciduous dentition agrees with clinical evidence that children are less sensitive to tooth stimulation than adults.     

The earliest Asian bats (Mammalia: Chiroptera) address major gaps in bat evolution

Bats dispersed widely after evolving the capacity for powered flight, and fossil bats are known from the early Eocene of most continents. Until now, however, bats have been conspicuously absent from the early Eocene of mainland Asia. Here, we report two teeth from the Junggar Basin of northern Xinjiang, China belonging to the first known early Eocene bats from Asia, representing arguably the most plesiomorphic bat molars currently recognized. These teeth combine certain bat synapomorphies with primitive traits found in other placental mammals, thereby potentially illuminating dental evolution among stem bats. The Junggar Basin teeth suggest that the dentition of the stem chiropteran family Onychonycteridae is surprisingly derived, although their postcranial anatomy is more primitive than that of any other Eocene bats. Additional comparisons with stem bat families Icaronycteridae and Archaeonycteridae fail to identify unambiguous synapomorphies for the latter taxa, raising the possibility that neither is monophyletic as currently recognized. The presence of highly plesiomorphic bats in the early Eocene of central Asia suggests that this region was an important locus for the earliest, transitional phases of bat evolution, as has been demonstrated for other placental mammal orders including Lagomorpha and Rodentia.     

Tooth wear and compensatory modification of the anterior dentoalveolar complex in humans

In populations living in environments where teeth wear severely, some compensatory modification of the dentoalveolar complex is thought to occur during life whereby functional occlusion is maintained as tooth substance is lost by wear. This study investigates one aspect of this modification process: Changes in the anterior dentoalveolar complex that are accompanied with wear were examined in a series of Japanese skeletal samples. In the prehistoric Japanese hunter-gatherer population heavy wear occurs over the entire dentition. The following changes were demonstrated to have occurred in the anterior segment of the dentition accompanied by wear on the anterior teeth: The anterior teeth tip lingually with wear up to a nearly upright position to fill in interproximal spaces that would have been generated by wear, and to maintain contact relations between adjacent teeth. At the same time, the anterior surface of the maxillary alveolar process also inclines lingually to a certain extent. The amount of lingual tipping is greater in the maxillary anterior teeth than in their mandibular antagonists. It is because of this discrepancy that, with age, the horizontal component of the overlap between maxillary and mandibular anterior teeth decreases, and their bite form changes from scissor bite to edge-to-edge bite. Lesser degrees of lingual tipping of the anterior teeth were also detected in the prehistoric agriculturists and historic Japanese populations. The variation in the degree of lingual tipping observed among the samples is explained by inter-population variation in severity and pattern of tooth wear. This and other evidence suggests that mechanisms that compensate for wear in the anterior dentition may be characteristic of all living human populations, independently of the degree of wear severity endured in their environments.     

Dental developmental pattern of the Neanderthal child from Roc de Marsal: a high-resolution 3D analysis

The assessment of the degree of similarity or difference between Neanderthals and modern humans in their patterns of dental development remains a controversial matter. Here we report results from the microtomographic-based (SR-μCT) high-resolution structural investigation of the maxilla and mandible of the Neanderthal child from Roc de Marsal, Dordogne, France (likely from OIS 5a). Following their virtual extraction and 3D rendering, we assessed the maturational stage of each of the 41 dental elements (20 deciduous and 21 permanent) forming its mixed dentition. By using a Bayesian approach, we calculated the probability that its deciduous and permanent mandibular sequences are found within the extant human variation as illustrated by a tomographic CT-based sub-sample of 32 children (deciduous dentition) and a panoramic radiographic- and CT-based whole sample of 343 living children (permanent dentition). Results show that neither the deciduous nor the permanent mandibular sequences displayed by Roc de Marsal are precisely found within our modern comparative files. In both sequences, the most influential factor is represented by a slight discrepancy in the Neanderthal child between the stage of mineralization of the first molar, which is proportionally advanced, and the maturational level reached by its incisors, which are proportionally delayed. Following a quantitative volumetric analysis of the deciduous teeth, we suggest that this characteristic may be related to differences between Neanderthals and modern humans in absolute dental size and relative size proportions between front and cheek teeth, as well as to structural differences in dental tissue proportions.     

The taming of the shrew milk teeth

SUMMARY A characteristic feature of mammalian dentition is the evolutionary reduction of tooth number and replacement. Because mice do not replace teeth, here we used Sorex araneus , the common shrew, as a model to investigate the loss of tooth replacement. Historically, shrews have been reported to initiate the development of several, milk or deciduous teeth but these soon become rudimentary and only the replacement teeth erupt. Shrews thus offer a living example of a derived mammalian pattern where the deciduous tooth development is being suppressed. Based on histological and gene expression analyses of serial sections, we suggest that S. araneus has discernible tooth replacement only in the premolar 4 (P4) position. Both generations of teeth express Shh in the enamel knot and in the inner enamel epithelium. Nevertheless, the deciduous P4 (dP4) is reduced in size during embryogenesis and is eventually lost without becoming functional. Analysis of growth shows that P4 replaces the dP4 in a "double-wedge" pattern indicative of competitive replacement where the suppression of the deciduous tooth coincides with the initiation of its replacement. Because activator–inhibitor mechanisms have been implicated in adjacent mouse molars and in transgenic mice with continuous tooth budding, we suggest that evolutionary suppression of deciduous teeth may involve early activation of replacement teeth, which in turn begin to suppress their deciduous predecessors.     

Report of inaccuracies in the study of the dentition of mammals

After discussing the existing view points and on the base of author's own studies, the designation of premolars and molars is proposed in the deciduous and permanent dentition of placental mammals, corresponding to the function, form, and structure of the teeth. With the admittance of the molars in the deciduous dentition of mammals, the discrepancy between milk dentition of mammals and humans is eliminated. In this way, the molars of deciduous dentition appeared to be the precursors of premolars and molars of permanent dentition. The separate groups of teeth are differentiated depending on the way of life and kind of consumed food, according to position and function of the teeth in the dentition. Lacerating teeth, premolars are formed in carnivora mammals for tearing off the food, and in case of intensive masticatory function of herbivora and omnivora, very likely, from the same germs of premolars, the molars are formed.     

The deciduous lower dentition of Ouranopithecus macedoniensis (Primates, Hominoidea) from the late Miocene deposits of Macedonia, Greece

Two mandibular fragments with associated milk teeth assigned to the late Miocene hominoid primate Ouranopithecus macedoniensis are analyzed. The fossils, which belong to a single individual, were found in the Vallesian locality of "Ravin de la Pluie" of the Axios Valley (Macedonia, Greece). The material is described here and compared with extant and extinct hominoids, allowing assessment of the evolutionary trends in the deciduous lower dentition within the Hominoidea. Hylobatids represent the more primitive pattern. Gorilla is slightly more derived than hylobatids, but less derived than Pongo and Pan, the latter being the most derived. With relatively smaller deciduous canines and more molarized deciduous premolars, Ouranopithecus is more derived than both Pan and Gorilla. Among the fossil hominoids, Proconsul, representing the primitive condition, has a very simple dp(3)and a dp(4)that has a trigonid that is taller than the talonid and which lacks a hypoconulid. Griphopithecus is more derived than Proconsul in having a dp(4) with a lower trigonid, a hypoconulid, and a less oblique cristid obliqua. Australopithecus and Paranthropus possess a similar morphology to that of Homo, while Ardipithecus appears to be more primitive than the latter genera. Ouranopithecus has a more derived lower milk dentition than Proconsul and Griphopithecus, but less derived than Australopithecus and Paranthropus. The comparison of the lower milk dentition of Ouranopithecus confirms our previous conclusions suggesting that this fossil hominoid shares derived characters with Australopithecus and Homo.     

Reduced tooth size in 45,X (Turner syndrome) females

Mean values and variances of deciduous and permanent tooth dimensions were compared between 121 45,X (Turner syndrome) females and 171 control subjects to clarify the role of the X chromosome on dental development. Although deciduous molars tended to be smaller than normal in 45,X females, there was no evidence of a reduction in tooth size for deciduous anterior teeth. In the permanent dentition, all mesiodistal dimensions were significantly smaller in 45,X females but only some of the buccolingual dimensions were smaller. The findings for deciduous tooth-size may reflect a sampling effect related to the extremely high frequency of spontaneous abortion in 45,X individuals. Results for permanent teeth are consistent with the concept of a decrease in enamel thickness in 45,X females.     

Deciduous dentition of a Late Archaic population of Ohio

I describe the developmental, metric, morphologic, and pathologic features of deciduous dentition in a terminal Late Archaic (c. 3000 B.P.) Native American population in Ohio. Development of deciduous dentition in this Late Archaic population is stable with little sequence variation. The pattern of development (ldc, ldp3, ldp4) cannot be shown to be different from a modern Euro-American sample. There is an indication, however, that the permanent first molar in the Late Archaic population developed somewhat more rapidly with respect to the deciduous teeth than in the Euro-American sample. Metric and morphologic features of deciduous dentition in the Late Archaic population appear typical for a population of northeast Asian descent. In general, these metric and morphologic features are shown to be useful in distinguishing among populations of differing ancestries. Developmental and acquired pathologic conditions of deciduous dentition are rare or absent in the Late Archaic population. Absence of linear enamel hypoplasia indicates sufficient access to basic resources for the younger children of this population, and the low frequency of caries reflects the relatively cariogenic-free nature of the diet of these hunter-gatherers.     

Coronal breadth of human primary anterior teeth

Original data for mesiodistal diameter of deciduous anterior teeth on 180 White children show: (1) mean size is smallest for the lower central incisor and largest for the upper canine, (2) means from combining widths on the left anterior teeth of each arch are larger in the maxilla than the mandible by 4.0 mm, (3) individual differences for widths of the upper central and lateral incisors extend from one child with these teeth of similar size to another child with the central incisor larger than the lateral by 2.3 mm, and (4) anterior tooth correlations are positive, varying from r = 0.4 for upper canine width with width of lower central incisor, to r = 0.8 for combined widths of left anterior teeth in the maxilla with combined widths of their antagonists. Comparative findings are drawn from investigations on Australian aborigines, South African Bushmen, Liberian Negroes, Tristan da Cunha islanders, Japanese, Japanese-Negro admixtures, Japanese-White admixtures, White groups living in several parts of Europe, and North American Whites. Among these ethnic groups, Australian aborigines have the largest deciduous anterior teeth. Composite means on each sex for North American Whites show boys to have slightly larger anterior deciduous teeth than girls.     

湖北长阳青铜时代人类乳齿特征的研究

对在湖北长阳县深潭湾崖葬墓出土的青铜时代人类乳齿形态特征的观察研究显示在人类恒齿出现的大多数具有种族识别价值的形态特征在乳齿有相等程度的表现,其中部分特征的出现率和表现程度高于恒齿。与其他地区人群相比,长阳青铜时代人类乳齿特征在总体上与东北亚人类具有的“中国型牙齿”特征接近。同时,在个别牙齿特征上呈现出南亚蒙古人种的特点。作者对产生这种现象的原因进行了分析。本文还就长阳青铜时代人类乳齿测量数据的表现特点进行了探讨。     

The size and morphology of the Nasioi dentition

Dental impressions were obtained on 240 Nasioi, a Melanesian population living on the island of Bougainville. Odontometric data are presented for both the permanent and deciduous teeth, and the former teeth are also examined morphologically. The results show that the Nasioi have large permanent teeth like other Australoid populations whereas the deciduous teeth are only of moderate size. The coefficients of variation are large in the permanent teeth compared to other populations but the sexual dimorphism in tooth size and variability is not remarkable. Morphologically, the permanent teeth of the Nasioi are characterized by a cusp number pattern, a high frequency of the Dryopithecus + pattern on the first mandibular molar, few individuals with a Cusp of Carabelli, and a moderate expression of shovelled-shaped anterior teeth.