A new detailed model for mammalian dentitional evolution

Westergaard, B.

doi:10.1111/j.1439-0469.1983.tb00276.x

Cited by 17 publications

(1 citation statement)

References 13 publications

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“…Often, evolutionary reductions tend to affect the last forming elements in a series (as, e.g., in evolutionary digit loss, 87), and this appears also to be the case for the dentition in placental mammals. Deciduous molars are initiated from the dental determinant (88) in a mesial direction, whilst the permanent molars develop in a distal direction (89), thus easily accounting for the evolutionary loss of the original P1 and P2. Incisors were originally initiated in both directions starting from the incisor determinant but the mesial expansion was lost, explaining the loss of the original I1 (89).…”

Section: Evolution Of Mammalian Dental Patterningmentioning

confidence: 99%

Dental agenesis: genetic and clinical perspectives

Coster

Marks

Martens

et al. 2008

J Oral Pathology Medicine

257

236

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Dental agenesis is the most common developmental anomaly in humans and is frequently associated with several other oral abnormalities. Whereas the incidence of missing teeth may vary considerably depending on dentition, gender, and demographic or geographic profiles, distinct patterns of agenesis have been detected in the permanent dentition. These frequently involve the last teeth of a class to develop (I2, P2, M3) suggesting a possible link with evolutionary trends. Hypodontia can either occur as an isolated condition (non-syndromic hypodontia) involving one (80% of cases), a few (less than 10%) or many teeth (less than 1%), or can be associated with a systemic condition or syndrome (syndromic hypodontia), essentially reflecting the genetically and phenotypically heterogeneity of the condition. Based on our present knowledge of genes and transcription factors that are involved in tooth development, it is assumed that different phenotypic forms are caused by different genes involving different interacting molecular pathways, providing an explanation not only for the wide variety in agenesis patterns but also for associations of dental agenesis with other oral anomalies. At present, the list of genes involved in human non-syndromic hypodontia includes not only those encoding a signaling molecule (TGFA) and transcription factors (MSX1 and PAX9) that play critical roles during early craniofacial development, but also genes coding for a protein involved in canonical Wnt signaling (AXIN2), and a transmembrane receptor of fibroblast growth factors (FGFR1). Our objective was to review the current literature on the molecular mechanisms that are responsible for selective dental agenesis in humans and to present a detailed overview of syndromes with hypodontia and their causative genes. These new perspectives and future challenges in the field of identification of possible candidate genes involved in dental agenesis are discussed.

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Section: Evolution Of Mammalian Dental Patterningmentioning

confidence: 99%

Dental agenesis: genetic and clinical perspectives

Coster

Marks

Martens

et al. 2008

J Oral Pathology Medicine

257

236

View full text Add to dashboard Cite

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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

Westergaard

Ferguson

1990

Am. J. Anat.

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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.

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Developmental mechanisms underlying tooth patterning in continuously replacing osteichthyan dentitions

Huysseune

Witten

2006

J Exp Zool Pt B

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The dentition of osteichthyans presents an astonishing diversity with regard to the distribution of teeth in the oral cavity, tooth numbers, arrangements, shapes, and sizes. Taking examples from three unrelated teleosts--the most speciose group of osteichthyans--and from the literature, this study explores how the initial tooth pattern is set up, and how this relates to the establishment and maintenance (or modification) of the tooth replacement pattern. In teleosts, first-generation teeth (the very first teeth in ontogeny to develop at a particular locus) are commonly initiated in adjacent or in alternate (odd and even) positions. The mechanisms responsible for these divergent developmental patterns remain to be elucidated, in particular, whether they reflect a field or local type of control. However, patterns of adjacent or alternate tooth initiation, set up by the first-generation teeth, can easily turn into replacement patterns where new teeth are initiated simultaneously every second, or even every third position, by synchronizing the formation of new first-generation teeth to the formation of replacement teeth at older loci. Our observations suggest that, once established, the replacement pattern appears to be maintained, as a kind of "default" state. Variations and modifications in this pattern are nevertheless common and suggest that tooth replacement is under local control, exerted at the level of the initiation of replacement teeth. Further studies are needed to test the hypothesis that regular replacement patterns are more frequent in association with the plesiomorphic condition of extramedullary replacement (replacement on the surface of the dentigerous bone) and more rare in the derived condition of intramedullary replacement (replacement within the medullary cavity of the dentigerous bone).

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A new detailed model for mammalian dentitional evolution

Cited by 17 publications

References 13 publications

Dental agenesis: genetic and clinical perspectives

Dental agenesis: genetic and clinical perspectives

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

Developmental mechanisms underlying tooth patterning in continuously replacing osteichthyan dentitions

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