Histological study on the chronology of the developing dentition in gorilla and orangutan

The single previous study on tooth development in great apes (Dean and Wood: Folia Primatol. (Basel) 36:111–127, 1981) is of limited value because it is based on cross-sectional radiographic data. This study considers problems in defining stages of tooth development in radiographs of developing ape dentitions and provides data on tooth chronology in Pongo pygmaeus and Gorilla gorilla by using histological methods of analysis. Crown formation times were estimated in individual teeth, and an overall chronology of dental development was found by registering teeth forming at the same time by using incremental growth lines. The earlier radiographic study correctly identified the molar and second premolar chronology and sequence in great apes, but significantly underestimated crown formation times in incisors, first premolars, and canine teeth in particular. Ape anterior tooth crowns take longer to form than the equivalent human teeth, but the overall dental developmental period in great apes is substantially shorter than in humans. Gorilla root extension rates appear to be fast, up to approximately 13 μm/day. This rapid root growth, associated with early tooth eruption, appears to be the developmental basis for the observed differences in timing between developing dentitions in great apes and humans.     

Dental topographic and three-dimensional geometric morphometric analysis of carnassialization in different clades of carnivorous mammals (Dasyuromorphia,Carnivora, Hyaenodonta)

The evolution of carnassial teeth in mammals, especially in the Carnivora, has been subject of many morphometric and some dental topographic studies. Here, we use a combination of dental topographic analysis (Dirichlet normal energy) and 3D geometric morphometrics of less and high carnassialized lower teeth of carnivoran, dasyuromorph and hyaenodont taxa. Carnassial crown curvature, as indicated by Dirichlet normal energy, is high in lesser carnassialized teeth and low in higher carnassialized teeth, where it is influenced by the reduction of crown features such as cusps and crests. PC1 of the geometric morphometric analysis is linked to enlargement of the carnassial blade, reduction of the talonid crushing basin and an increasingly asymmetric cervix line with an enlarged mesial flexure in more carnassialized teeth. Distribution of PC1 values further indicates that along the tooth row of dasyuromorphs (m2–m4) and hyaenodonts (m1–m3) the most distal carnassial is the most carnassialized (principal carnassial), and in most taxa with overall higher carnassialized teeth, carnassialization successively increases from the anterior to the posterior tooth position along the tooth row. PC2 indicates that a longitudinal elongated carnassial is present in caniforms and in unspecialized feliforms, which separates these taxa in morphospace from all dasyuromorphs, hyaenodonts and specialized feliforms. An ancestral state reconstruction shows that this longitudinal elongation may be a plesiomorphic ancestral state for the Carnivora, which is different from the Dasyuromorphia and the Hyaenodonta. This elongation, enabling the presence of a longitudinally aligned carnassial blade as well as a complete talonid basin, might have provided the Carnivora with an advantage in terms of adaptive versatility.     

Tooth development in a scincid lizard, Chalcides viridanus (Squamata), with particular attention to enamel formation

Comparative analysis of tooth development in the main vertebrate lineages is needed to determine the various evolutionary routes leading to current dentition in living vertebrates. We have used light, scanning and transmission electron microscopy to study tooth morphology and the main stages of tooth development in the scincid lizard, Chalcides viridanus, viz., from late embryos to 6-year-old specimens of a laboratory-bred colony, and from early initiation stages to complete differentiation and attachment, including resorption and enamel formation. In C. viridanus, all teeth of a jaw have a similar morphology but tooth shape, size and orientation change during ontogeny, with a constant number of tooth positions. Tooth morphology changes from a simple smooth cone in the late embryo to the typical adult aspect of two cusps and several ridges via successive tooth replacement at every position. First-generation teeth are initiated by interaction between the oral epithelium and subjacent mesenchyme. The dental lamina of these teeth directly branches from the basal layer of the oral epithelium. On replacement-tooth initiation, the dental lamina spreads from the enamel organ of the previous tooth. The epithelial cell population, at the dental lamina extremity and near the bone support surface, proliferates and differentiates into the enamel organ, the inner (IDE) and outer dental epithelium being separated by stellate reticulum. IDE differentiates into ameloblasts, which produce enamel matrix components. In the region facing differentiating IDE, mesenchymal cells differentiate into dental papilla and give rise to odontoblasts, which first deposit a layer of predentin matrix. The first elements of the enamel matrix are then synthesised by ameloblasts. Matrix mineralisation starts in the upper region of the tooth (dentin then enamel). Enamel maturation begins once the enamel matrix layer is complete. Concomitantly, dental matrices are deposited towards the base of the dentin cone. Maturation of the enamel matrix progresses from top to base; dentin mineralisation proceeds centripetally from the dentin–enamel junction towards the pulp cavity. Tooth attachment is pleurodont and tooth replacement occurs from the lingual side from which the dentin cone of the functional teeth is resorbed. Resorption starts from a deeper region in adults than in juveniles. Our results lead us to conclude that tooth morphogenesis and differentiation in this lizard are similar to those described for mammalian teeth. However, Tomes processes and enamel prisms are absent.     

First evidence of the tooth eruption sequence of the upper jaw in Hyaenodon (Hyaenodontidae,Mammalia) and new information on the ontogenetic development of its dentition

Juvenile material with the main focus on the upper jaw of the fossil predator Hyaenodon was evaluated to study the tooth eruption sequence and to examine the ontogeny of its dentition in detail. The comparison in size of milk to permanent teeth indicates a growth rate of 12–16 % in Hyaenodon. The thin section of a deciduous canine of a North American taxon shows four dental rings. Based on the knowledge of recent carnivores, this implies an age of 3–4 years in the last stage of tooth eruption and thus a long juvenile phase. The mandibles ascertained the most recent established tooth eruption sequence for North American and European species. For the first time ever, juvenile material from Asia is documented and interpreted. This study likewise shows a difference in the sequence of the upper jaw: the first upper premolar erupts before the first upper molar in North American species, whereas the European taxa show an earlier eruption of the first upper molar. This fact further confirms the divergence between the Hyaenodon lineages from North America and Europe.     

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.     

Growth factors and tooth development

The effects of various growth factors on tooth development were studied in organ cultures of mouse embryonic tooth germs. Transferrin was shown to be a necessary growth factor for early tooth morphogenesis. Transferrin was required for the development of bud- and early cap-staged teeth, and it was shown to be the only serum protein that was needed by early cap-staged teeth in organ culture. Promotion of tooth morphogenesis and dental cell differentiation was shown to be based on the stimulation of cell proliferation. The roles of polypeptide growth factors in tooth development were studied by adding these factors to the transferrin-containing chemically-defined culture medium which supports early tooth morphogenesis and cell differentiation. Fibroblast growth factor or platelet-derived growth factor did not affect cell proliferation or morphogenesis of tooth germs in culture. On the contrary, epidermal growth factor (EGF) stimulated cell proliferation in tooth explants, but at the same time inhibited tooth morphogenesis and dental cell differentiation. Autoradiographic localization of proliferating cells revealed that dental tissues responded to EGF with different proliferation rates. The responsiveness to EGF was stage-dependent, early cap-staged teeth were sensitive to EGF but late cap-staged and bell-staged teeth developed normally in the presence of EGF in the culture medium. The presence and distribution of receptors for both transferrin and EGF were studied in mouse embryonic teeth at various developmental stages by incubating freshly-separated tooth germs with 125Iodine-labeled transferrin or EGF, and then processing the tissues for autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)     

Innervation of the human upper primary dentition: Implications for understanding tooth initiation and rethinking growth and eruption patterns

Recent comparisons of humans with apes and early fossil hominids have prompted renewed interest in the study of sequences of dental growth and development. Such comparisons, however, rely on certain assumptions about tooth development and dental homology and the biological reality of distinguishing “deciduous” from “permanent” teeth. In light of earlier suggestions by Schwartz that there might be a correlation between nerves and the stem progenitors of tooth classes, and thus between nerve branch number and number of tooth classes, we studied a large sample of ～ 3 month fetuses to elucidate the nature of nerve branching patterns and the development of the primary dentition (i.e., the “deciduous” incisors, canine, and molars, and the first “permanent” molar). Contrary to expectation, variation in nerve branch patterning was the rule. If nerve fibers do have a role in tooth development, it can only be at the time of initiation, with definitive innervation occurring late in tooth development. In taking into consideration the entire span of tooth development—from initiation to innervation to eruption—and the process by which successional teeth arise (each from the external dental epithelium of a predecessor tooth), we suggest that dividing tooth growth and eruption into patterns of the “deciduous” teeth vs. those of the “permanent” is artificial and that a more meaningful approach would be the study of the entire dentition.     

The developing dentition and tooth structure in hominoids

This review of hominoid dental development is presented in two parts. The first section reviews (1) the general relationship between dental development and life history in hominoids; (2) the methods used to document dental development, and (3) the nature of incremental growth markings in hominoid teeth. The second section builds on this and reviews the contributions to hominoid dental development that have been made by (1) studies of tooth emergence; (2) studies of tooth calcification stages, and (3) histological studies of incremental growth markings made either from sections of teeth or replicas of early hominid teeth prepared for scanning electron microscopy.     

Dentition and histology in titanosaurian dinosaur embryos from Upper Cretaceous of Patagonia,Argentina

Abstract: Exceptionally preserved sauropod embryos from the Late Cretaceous Anacleto Formation in Auca Mahuevo (Neuquén Province, Argentina) have provided fundamental information on titanosaurian ontogeny. This paper describes the dental composition, disposition and microstructure of the specimens. Embryonic teeth show size disparity, with lengths that vary from 1 to 3 mm and diameters ranging from 0.15 to 0.26 mm, with the most frequent length values between 2.5 and 3 mm. Apparently, a typical ‘pencil‐like’ tooth morphology and a dental formula of Pm 4, M 7–8/D10? remained constant during titanosaurian ontogeny, whereas the arrangement of teeth in the skull shows notable ontogenetic changes. Absence of wear facets on teeth suggests a lack of prenatal chewing movements. The enamel proportion is significantly higher in embryos than in mature titanosaurs, which suggests that this relationship varies during ontogeny. Embryonic bony tissue is composed of highly vascularized, cellular woven bone. The absence of osteonal tissue, the high degree of vascularization, the presence of numerous osteocytes and poor development of periosteal bone reveals that the Auca Mahuevo titanosaurs would have had a high early growth rate and that they were buried at a relatively advanced embryonic stage.     

Schultz's unruly rule: dental developmental sequences and schedules in small-bodied, folivorous lemurs

Schultz's rule (as reconstructed by Smith) states that there is a relationship between the pattern (or relative order) of eruption of molar versus secondary (replacement) teeth and the overall pace (or absolute timing) of growth and maturation. Species with 'fast' life histories (rapid dental development, rapid growth, early sexual maturation, short life spans) are said to exhibit relatively early eruption of the molars and late eruption of the secondary replacement teeth (premolars, canines, incisors), whereas species with 'slow' life histories are said to exhibit relatively late eruption of the molars and early eruption of the secondary dentition. In a recent review, B.H. Smith noted that primates with tooth combs might violate this rule because tooth combs tend to erupt early, regardless of the pace of life history. We show that exceptions to Schultz's rule among lemurs are not limited to the relative timing of eruption of the tooth comb. Rather, among lemurs, some species with extremely accelerated dental development exhibit a pattern of eruption of molars and of secondary teeth in direct opposition to the expectations of Schultz's rule. We focus particularly on the pattern (order) and pace (absolute timing) of dental development and eruption in Avahi and Lepilemur - two relatively small, nocturnal folivores with rapid dental development. These taxa differ markedly in their eruption sequences (the premolars erupt after M2 and M3 in Lepilemur but not Avahi ). We offer an explanation for the failure of Schultz's rule to predict these differences. Schultz's rule presumes that eruption timing is dependent on the size of the jaw and that, therefore, molar crown formation and eruption will be delayed in species with slow-growing jaws. We show that a variety of processes (including developmental imbrication) allows the crowns of permanent teeth to form and to erupt into jaws that might appear to be too small to accommodate them.     

Development of the dentition in Alligator mississippiensis: upper jaw dental and craniofacial development in embryos, hatchlings, and young juveniles, with a comparison to lower jaw development

Development of the upper dentition in Alligator mississippiensis was investigated using a close series of accurately staged and aged embryos, hatchlings, and young juveniles up to 11 days posthatching, as well as some young and old adult specimens. Studies from scanning electron microscopy, light microscopy, acetate and computer reconstructions, radiography and macroscopy were combined to elucidate the details of embryonic dental development, tooth initiation pattern, dentitional growth, and erupted functional dentition. The results were compared with those from the lower jaw and related to the development of other craniofacial structures. Approximately 17 early teeth in each jaw half develop as surface teeth, of which 13 project for 1 to 12 days before sinking into the mesenchyme. The first three teeth initiate directly from the oral epithelium at Ferguson stages 14-15 (days 15-19 after egg laying), before there is any local trace of dental lamina formation. All other teeth develop from a dental prolamina or lamina; and with progressive lamina development, submerged teeth initiate from the aboral end leading to the formation of replacement teeth. All teeth form dentin matrix, but 12 early teeth do not form enamel. Approximately 20 embryonic teeth are resorbed, 6 are transitional, and 42 function for longer periods after hatching. The embryonic tooth initiation pattern (illustrated by defining a tooth position formula) does not support the previous models of Odontostichi, Zahnreihen, and Tooth Families, each of which postulates perfect regularity. Up to three interstitial tooth positions develop between sites of primary tooth initiation, and families with up to five generations at hatching are at first arbitrarily defined.     

Fate of the Molar Dental Lamina in the Monophyodont Mouse

The successional dental lamina (SDL) plays an essential role in the development of replacement teeth in diphyodont and polyphyodont animals. A morphologically similar structure, the rudimental successional dental lamina (RSDL), has been described in monophyodont (only one tooth generation) lizards on the lingual side of the developing functional tooth. This rudimentary lamina regresses, which has been proposed to play a role in preventing the formation of future generations of teeth. A similar rudimentary lingual structure has been reported associated with the first molar in the monophyodont mouse, and we show that this structure is common to all murine molars. Intriguingly, a lingual lamina is also observed on the non-replacing molars of other diphyodont mammals (pig and hedgehog), initially appearing very similar to the successional dental lamina on the replacing teeth. We have analyzed the morphological as well as ultrastructural changes that occur during the development and loss of this molar lamina in the mouse, from its initiation at late embryonic stages to its disappearance at postnatal stages. We show that loss appears to be driven by a reduction in cell proliferation, down-regulation of the progenitor marker Sox2, with only a small number of cells undergoing programmed cell death. The lingual lamina was associated with the dental stalk, a short epithelial connection between the tooth germ and the oral epithelium. The dental stalk remained in contact with the oral epithelium throughout tooth development up to eruption when connective tissue and numerous capillaries progressively invaded the dental stalk. The buccal side of the dental stalk underwent keratinisation and became part of the gingival epithelium, while most of the lingual cells underwent programmed cell death and the tissue directly above the erupting tooth was shed into the oral cavity.     

Longitudinal study of dental development in chimpanzees of known chronological age: Implications for understanding the age at death of Plio-Pleistocene hominids

Reconstruction of life history variables of fossil hominids on the basis of dental development requires understanding of and comparison with the pattern and timing of dental development among both living humans and pongids. Whether dental development among living apes or humans provides a better model for comparison with that of Plio-Pleistocene hominids of the genus Australopithecus remains a contentious point. This paper presents new data on chimpanzees documenting developmental differences in the dentitions of modern humans and apes and discusses their significance in light of recent controversies over the human or pongid nature of australopithecine dental development. Longitudinal analysis of 299 lateral head radiographs from 33 lab-reared chimpanzees (Pan troglodytes) of known chronological age allows estimation of means and standard deviations for the age at first appearance of 8 developmental stages in the mandibular molar dentition. Results are compared with published studies of dental development among apes and with published standards for humans. Chimpanzees are distinctly different from humans in two important aspects of dental development. Relative to humans, chimpanzees show advanced molar development vis a vis anterior tooth development, and chimpanzees are characterized by temporal overlap in the calcification of adjacent molar crowns, while humans show moderate to long temporal gaps between the calcification of adjacent molar crowns. In combination with recent work on enamel incremental markers and CAT scans of developing dentitions of Plio-Pleistocene hominids, this evidence supports an interpretation of a rapid, essentially “apelike” ontogeny among australopithecines. © 1996 Wiley-Liss, Inc.     

Contribution of mesoderm to the developing dental papilla

Teeth develop from epithelium and neural crest-derived mesenchyme via a series of reciprocal epithelial-mesenchymal interactions. The majority of the dental papilla of the tooth has been demonstrated to be of neural crest origin. However, non-neural crest cells have also been observed in this region from the bud stage of tooth development onwards. The number of these non-neural crest-derived cells rises as the dental papilla develops. However, their origin is unknown. We have followed migration of cells into the tooth in vitro using DiI to fate map regions surrounding the developing tooth. To identify the contribution of mesodermally-derived cells, we have utilised Mesp1cre/R26R transgenic reporter mice. We document that cells outside the early tooth primordium migrate into the developing dental papilla from the late cap stage of development. Here, we show that migrating cells are mesodermally-derived and create a network of endothelial cells, forming the blood vessels of the tooth. No cells of mesodermal origin were present in the condensed mesenchyme surrounding the dental epithelium until the cap stage of tooth development. Mesodermally-derived cells start invading the dental papilla at the late cap stage, providing the blood supply to the dental pulp. Endothelial cells are able to invade the developing dental papilla in vitro using the slice culture method. Understanding the origin and timing of migration of the mesodermally-derived cells is an important advance in our understanding of how a tooth develops and is particularly relevant to studies which aim to create bioengineered teeth.     

Plate-like permanent dental laminae of upper jaw dentition in adult gobiid fish, Sicyopterus japonicus

Sicyopterus japonicus (Teleostei, Gobiidae) possesses a unique upper jaw dentition different from that known for any other teleosts. In the adults, many (up to 30) replacement teeth, from initiation to attachment, are arranged orderly in a semicircular-like strand within a capsule of connective tissue on the labial side of each premaxillary bone. We have applied histological, ultrastructural, and three-dimensional imaging from serial sections to obtain insights into the distribution and morphological features of the dental lamina in the upper jaw dentition of adult S. japonicus. The adult fish has numerous permanent dental laminae, each of which is an infolding of the oral epithelium at the labial side of the functional tooth and forms a thin plate-like structure with a wavy contour. All replacement teeth of a semicircular-like strand are connected to the plate-like dental lamina by the outer dental epithelium and form a tooth family; neighboring tooth families are completely separated from each other. The new tooth germ directly buds off from the ventro-labial margin of the dental lamina, whereas no distinct free end of the dental lamina is present, even adjacent to this region. Cell proliferation concentrated at the ventro-labial margin of the dental lamina suggests that this region is the site for repeated tooth initiation. During tooth development, the replacement tooth migrates along a semicircular-like strand and eventually erupts through the dental lamina into the oral epithelium at the labial side of the functional tooth. This unique thin plate-like permanent dental lamina and the semicircular-like strand of replacement teeth in the upper jaw dentition of adult S. japonicus probably evolved as a dental adaptation related to the rapid replacement of teeth dictated by the specialized feeding habit of this algae-scraping fish.     

Dental histology of Coelophysis bauri and the evolution of tooth attachment tissues in early dinosaurs

Studies of dinosaur teeth have focused primarily on external crown morphology and thus, use shed or in situ tooth crowns, and are limited to the enamel and dentine dental tissues. As a result, the full suites of periodontal tissues that attach teeth to the jaws remain poorly documented, particularly in early dinosaurs. These tissues are an integral part of the tooth and thus essential to a more complete understanding of dental anatomy, development, and evolution in dinosaurs. To identify the tooth attachment tissues in early dinosaurs, histological thin sections were prepared from the maxilla and dentary of a partial skull of the early theropod Coelophysis bauri from the Upper Triassic (Rhaetian‐ 209–201 Ma) Whitaker Quarry, New Mexico, USA. As one of the phylogenetically and geologically oldest dinosaurs, it is an ideal candidate for examining dental tissues near the base of the dinosaurian clade. The teeth of C. bauri exhibited a fibrous tooth attachment in which the teeth possessed five tissues: enamel, dentine, cementum, periodontal ligament (PDL), and alveolar bone. Our findings, coupled with those of more recent studies of ornithischian teeth, indicate that a tripartite periodontium, similar to that of crocodilians and mammals, is the plesiomorphic condition for dinosaurs. The occurrence of a tripartite periodontium in dinosaurs adds to the growing consensus that the presence of these tissues is the plesiomorphic condition for the major amniote clades. Furthermore, this study establishes the relative timing of tissue development and growth directions of periodontal tissues and provides the first comparative framework for future studies of dinosaur periodontal development, tooth replacement, and histology. J. Morphol. 277:916–924, 2016. © 2016 Wiley Periodicals, Inc.     

Early development and replacement of the stickleback dentition

Teeth have long served as a model system to study basic questions about vertebrate organogenesis, morphogenesis, and evolution. In nonmammalian vertebrates, teeth typically regenerate throughout adult life. Fish have evolved a tremendous diversity in dental patterning in both their oral and pharyngeal dentitions, offering numerous opportunities to study how morphology develops, regenerates, and evolves in different lineages. Threespine stickleback fish (Gasterosteus aculeatus) have emerged as a new system to study how morphology evolves, and provide a particularly powerful system to study the development and evolution of dental morphology. Here, we describe the oral and pharyngeal dentitions of stickleback fish, providing additional morphological, histological, and molecular evidence for homology of oral and pharyngeal teeth. Focusing on the ventral pharyngeal dentition in a dense developmental time course of lab‐reared fish, we describe the temporal and spatial consensus sequence of early tooth formation. Early in development, this sequence is highly stereotypical and consists of seventeen primary teeth forming the early tooth field, followed by the first tooth replacement event. Comparing this detailed morphological and ontogenetic sequence to that described in other fish reveals that major changes to how dental morphology arises and regenerates have evolved across different fish lineages. J. Morphol. 277:1072–1083, 2016. © 2016 Wiley Periodicals, Inc.     

Ontogeny, anatomy and attachment of the dentition in mosasaurs (Mosasauridae: Squamata)

Aspects of mosasaur dental ontogeny are well preserved in many fossils of these giant marine squamates. Replacement teeth on the tooth-bearing elements (TBEs) first appear as small enamel crowns positioned posterolingual to the attached tooth (posterolabial for the pterygoid). Several developing crowns, of progressively larger size, are aligned in rows relating to a specific tooth position. The crowns rest in a dental groove that varies in width and depth depending on the TBE. The crown closest to the attached tooth is always the largest and is found in a small resorption pit. As resorption proceeds, the pit expands in volume (cementum and alveolar bone), and the crown increases in size and settles into the pit. Once mature crown size is achieved, the dentine root and cementum portion of the root develop rapidly, the attached tooth is lost and the replacement tooth erupts out of the alveolus. Mosasaurid teeth develop along a 'zig-zag'-shaped movement path: horizontally along the dental groove, down into the alveolus, and up and out of the alveolus prior to attachment to the alveolar wall. At no point in mosasaurid tooth development are the crowns observed in a horizontal position. The mosasaurid dental lamina appears to have been a continuous strip of dental epithelium as it is in other squamates. Mosasaurid tooth attachment is thecodont (histologically and geometrically) not subpleurodont. Most aspects of mosasaurid tooth attachment and ontogeny are autapomorphic for the group.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 149 , 687–700.     

Dental anomalies in the gray foxUrocyon cinereoargenteus and the red foxVulpes vulpes

We examined dental anomalies, including oligodonty, polydonty, connation, rotation, and misalignment in 510 gray foxes and 150 red foxes from southern Illinois (USA). Dental anomalies were significantly more common (x ² = 11.5, df = 1,p < 0.001) in gray foxes (n = 177; 34.7% of sample) than red foxes (n = 25; 16.6% of sample), and more common in male than female gray foxes (x ² = 3.88, df = 1,p < 0.05). Polydonty was very uncommon, as expected for species in which the normal dental complement is close to the primitive eutherian number. In both species, the most prevalent anomaly was loss of the last lower molar. Loss of the upper or lower first premolar was also common. Thus, oligodonty almost always involved the smaller anterior (P¹ and P₁) or posterior (M₃) teeth of the dental arcade. Conversely, the large carnassial teeth, with complex occlusal patterns and shearing surfaces, appeared to be highly conserved with only three anomalous individuals (0.4%) among all specimens.     

Gene expression patterns associated with suppression of odontogenesis in mouse and vole diastema regions

Rodents have a toothless diastema region between the incisor and molar teeth which may contain rudimentary tooth germs. We found in upper diastema region of the mouse (Mus musculus) three small tooth germs which developed into early bud stage before their apoptotic removal, while the sibling vole (Microtus rossiaemeridionalis) had only a single but larger tooth germ in this region, and this developed into late bud stage before regressing apoptotically. To analyze the genetic mechanisms of the developmental arrest of the rudimentary tooth germs we compared the expression patterns of several developmental regulatory genes (Bmp2, Bmp4, Fgf4, Fgf8, Lef1, Msx1, Msx2, p21, Pitx2, Pax9 and Shh) between molars and diastema buds of mice and voles. In diastema tooth buds the expression of all the genes differed from that of molars. The gene expression patterns suggest that the odontogenic program consists of partially independent signaling cascades which define the exact location of the tooth germ, initiate epithelial budding, and transfer the odontogenic potential from the epithelium to the underlying mesenchyma. Although the diastema regions of the two species differed, in both species the earliest difference that we found was weaker expression of mesenchymal Pax9 in the diastema region than in molar and incisor regions at the dental lamina stage. However, based on earlier tissue recombination experiments it is conceivable that the developmental arrest is determined by the early oral epithelium. Received: 1 February 1999 / Accepted: 30 March 1999