Animal tooth development

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Time-lapse imaging of a developing tooth germ derived from a mouse embryo

Tooth development or odontogenesis is the process in which teeth develop and grow into the mouth. Tooth development varies among species.

Contents

Tooth development in vertebrates

Fish

In fish, Hox gene expression regulates mechanisms for tooth initiation. [1] [2]

However, sharks continuously produce new teeth throughout their lives [3] [4] [5] via a drastically different mechanism. Shark teeth form from modified scales near the tongue and move outward on the jaw in rows until they are eventually dislodged. [6] Their scales, called dermal denticles, and teeth are homologous organs. [7]

Mammals

Generally, tooth development in non-human mammals is similar to human tooth development. The variations usually lie in the morphology, number, development timeline, and types of teeth. [8] However, some mammals' teeth do develop differently than humans'.

In mice, WNT signals are required for the initiation of tooth development. [9] [10] Rodents' teeth continually grow, forcing them to wear down their teeth by gnawing on various materials. [11] If rodents are prevented from gnawing, their teeth eventually puncture the roofs of their mouths. In addition, rodent incisors consist of two halves, known as the crown and root analogues. The labial half is made of enamel and resembles a crown, while the lingual half is made of dentin and resembles a root. The mineral distribution in rodent enamel is different from that of monkeys, dogs, pigs, and humans. [12]

In horse teeth, enamel and dentin layers are intertwined, which increases the strength and decreases the wear rate of the teeth. [13] [14] Contrary to popular belief, horse teeth do not "grow" indefinitely. Rather, existing tooth erupts from below the gumline. Horses start to "run out" of erupting tooth in their early 30s and in the rare case they live long enough, the roots of their teeth will fall out completely in the middle to latter part of their third decade.

In manatees, mandibular molars develop separately from the jaw and are encased in a bony shell separated by soft tissue. This also occurs in elephants' successional teeth, which erupt to replace worn teeth. Elephants have six sets of molars in their life, all of which grown from the back of their mouth and are then pushed forward. [15]

All members of the order Tubulidentata have no incisors or canines, their teeth have no enamel, and their molars grow continuously from the root. [16]

Human tooth development

When it comes to tooth development in humans, there are many differences in the way humans and other primates' teeth develop slowly over the beginning of their life. Once the dental tissue in primates and humans is formed, there are little changes made throughout the remainder of the organism's lifetime, but there are still factors such as tooth wear and dental disease can alter the dental tissue of primates. [17] The dental tissue in primates is a layered structure, and scientists are able to observe the layered structure chronologically to learn about the detailed development of their teeth. This layered structure is preserved throughout life for humans and primates.

Invertebrate "teeth"

True teeth are unique to vertebrates, [18] although some invertebrates have analogous structures sometimes called "teeth". The organism with the simplest genome bearing such "teeth" is probably the worm genus Ancylostoma (Ancylostoma duodenale, Necator americanus). [19] Molluscs have a structure called a radula which bears a ribbon of chitinous "teeth". However, these are histologically and developmentally different from vertebrate teeth, and are unlikely to be homologous. For example, vertebrate teeth develop from a neural crest mesenchyme-derived dental papilla, and the neural crest is specific to vertebrates, as are tissues such as enamel. [18]

Variation of tooth development across species

The study of tooth development across different species, invertebrates, and vertebrates indicates that tooth development varies greatly across different types of organisms. Organisms may vary from having few to no teeth at all to organisms that go through life with multiple layers of teeth. In some unique cases there are species with teeth that regenerate throughout their lifetime. Because of this, it is very important that scientists select specific species to study that may provide them with information as to how similar species' tooth development takes place. These organisms are chosen based on their specific early dental specification as well as tooth replacement ability. With an organism that has the ability to regenerate teeth, scientists have a unique opportunity to continuously study the specific odontogenic processes and mechanisms that lead to the development of teeth in different vertebrates. [20]

Genetics

In reptilian tooth development, some scientist have chosen to determine the location and function of the SHH gene as well as the odontogenic band to help collect information on how reptiles develop teeth at a young age. [20] The SHH gene gives instructions to produce a protein known as the Sonic Hedgehog protein, and this protein's function is to aid in certain required embryonic development processes. The SHH gene and proteins play major roles in not only the tooth development of organisms, but they also help in cell growth, specialization, and patterning of an organism's body. [21]

See also

Related Research Articles

<span class="mw-page-title-main">Molar (tooth)</span> Large tooth at the back of the mouth

The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name molar derives from Latin, molaris dens, meaning "millstone tooth", from mola, millstone and dens, tooth. Molars show a great deal of diversity in size and shape across the mammal groups. The third molar of humans is sometimes vestigial.

<span class="mw-page-title-main">Cementum</span> Specialized calcified substance covering the root of a tooth

Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.

<span class="mw-page-title-main">Tooth enamel</span> Major tissue that makes up part of the tooth in humans and many animals

Tooth enamel is one of the four major tissues that make up the tooth in humans and many animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, cementum, and dental pulp. It is a very hard, white to off-white, highly mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation, especially by acids from food and drink. In rare circumstances enamel fails to form, leaving the underlying dentin exposed on the surface.

<span class="mw-page-title-main">Sonic hedgehog protein</span> Signaling molecule in animals

Sonic hedgehog protein (SHH) is encoded for by the SHH gene. The protein is named after the video game character Sonic the Hedgehog.

<span class="mw-page-title-main">Dentin</span> Calcified tissue of the body; one of the four major components of teeth

Dentin or dentine is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by enamel on the crown and cementum on the root and surrounds the entire pulp. By volume, 45% of dentin consists of the mineral hydroxyapatite, 33% is organic material, and 22% is water. Yellow in appearance, it greatly affects the color of a tooth due to the translucency of enamel. Dentin, which is less mineralized and less brittle than enamel, is necessary for the support of enamel. Dentin rates approximately 3 on the Mohs scale of mineral hardness. There are two main characteristics which distinguish dentin from enamel: firstly, dentin forms throughout life; secondly, dentin is sensitive and can become hypersensitive to changes in temperature due to the sensory function of odontoblasts, especially when enamel recedes and dentin channels become exposed.

<span class="mw-page-title-main">Pulp (tooth)</span> Part in the center of a tooth made up of living connective tissue and cells called odontoblasts

The pulp is the connective tissue, nerves, blood vessels, and odontoblasts that comprise the innermost layer of a tooth. The pulp's activity and signalling processes regulate its behaviour.

<span class="mw-page-title-main">Ameloblast</span> Cells which deposit enamel during tooth development

Ameloblasts are cells present only during tooth development that deposit tooth enamel, which is the hard outermost layer of the tooth forming the surface of the crown.

<span class="mw-page-title-main">Enamel organ</span> Aggregate of cells involved in tooth development

The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum. The enamel organ is responsible for the formation of enamel, initiation of dentine formation, establishment of the shape of a tooth's crown, and establishment of the dentoenamel junction.

<span class="mw-page-title-main">Dental lamina</span> Band of epithelial tissue

The dental lamina is a band of epithelial tissue seen in histologic sections of a developing tooth. The dental lamina is first evidence of tooth development and begins at the sixth week in utero or three weeks after the rupture of the buccopharyngeal membrane. It is formed when cells of the oral ectoderm proliferate faster than cells of other areas. Best described as an in-growth of oral ectoderm, the dental lamina is frequently distinguished from the vestibular lamina, which develops concurrently. This dividing tissue is surrounded by and, some would argue, stimulated by ectomesenchymal growth. When it is present, the dental lamina connects the developing tooth bud to the epithelium of the oral cavity. Eventually, the dental lamina disintegrates into small clusters of epithelium and is resorbed. In situations when the clusters are not resorbed, eruption cysts are formed over the developing tooth and delay its eruption into the oral cavity. This invagination of ectodermal tissues is the progenitor to the later ameloblasts and enamel while the ectomesenchyme is responsible for the dental papilla and later odontoblasts.

<span class="mw-page-title-main">Human tooth development</span> Process by which teeth form

Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth week of prenatal development, and permanent teeth begin to form in the twentieth week. If teeth do not start to develop at or near these times, they will not develop at all, resulting in hypodontia or anodontia.

The neonatal line is a particular band of incremental growth lines seen in histologic sections of both enamel and dentin of primary teeth. It belongs to a series of a growth lines in tooth enamel known as the Striae of Retzius denoting the prolonged rest period of enamel formation that occurs at the time of birth. The neonatal line is darker and larger than the rest of the striae of retzius. The neonatal line is the demarcation between the enamel formation before birth and after birth i.e., prenatal and postnatal enamel respectively. It is caused by the different physiologic changes at birth and is used to identify enamel formation before and after birth. The position of the neonatal line differs from tooth to tooth

<span class="mw-page-title-main">Odontoblast</span> Type of cell that produces dentin in teeth

In vertebrates, an odontoblast is a cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the formation of dentin, the substance beneath the tooth enamel on the crown and the cementum on the root.

<span class="mw-page-title-main">Dental follicle</span> Anatomical entity

The dental follicle, also known as dental sac, is made up of mesenchymal cells and fibres surrounding the enamel organ and dental papilla of a developing tooth. It is a vascular fibrous sac containing the developing tooth and its odontogenic organ. The dental follicle (DF) differentiates into the periodontal ligament. In addition, it may be the precursor of other cells of the periodontium, including osteoblasts, cementoblasts and fibroblasts. They develop into the alveolar bone, the cementum with Sharpey's fibers and the periodontal ligament fibers respectively. Similar to dental papilla, the dental follicle provides nutrition to the enamel organ and dental papilla and also have an extremely rich blood supply.

<span class="mw-page-title-main">Dentinogenesis imperfecta</span> Genetic disorder impairing tooth development

Dentinogenesis imperfecta (DI) is a genetic disorder of tooth development. It is inherited in an autosomal dominant pattern, as a result of mutations on chromosome 4q21, in the dentine sialophosphoprotein gene (DSPP). It is one of the most frequently occurring autosomal dominant features in humans. Dentinogenesis imperfecta affects an estimated 1 in 6,000-8,000 people.

<span class="mw-page-title-main">Postcanine megadontia</span> Relative enlargement of pre-molars and molars compared with other teeth.

Post-canine megadontia is a relative enlargement of the molars and premolars compared to the size of the incisors and canines. This phenomenon is seen in some early hominid ancestors such as Paranthropus aethiopicus.

<span class="mw-page-title-main">Tooth</span> Hard structure of the mouth

A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic germ layer, the ectoderm.

<span class="mw-page-title-main">Fish scale</span> Rigid covering growing atop a fishs skin

A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as well as possible hydrodynamic advantages. The term scale derives from the Old French escale, meaning a shell pod or husk.

<span class="mw-page-title-main">Mammal tooth</span> Details of teeth found in many warm-blooded vertebrate animals

Teeth are common to most vertebrates, but mammalian teeth are distinctive in having a variety of shapes and functions. This feature first arose among early therapsids during the Permian, and has continued to the present day. All therapsid groups with the exception of the mammals are now extinct, but each of these groups possessed different tooth patterns, which aids with the classification of fossils.

<span class="mw-page-title-main">Dinosaur tooth</span> Subject of dental study in paleontology

Dinosaur teeth have been studied since 1822 when Mary Ann Mantell (1795-1869) and her husband Dr Gideon Algernon Mantell (1790-1852) discovered an Iguanodon tooth in Sussex in England. Unlike mammal teeth, individual dinosaur teeth are generally not considered by paleontologists to be diagnostic to the genus or species level for unknown taxa, due morphological convergence and variability between teeth. and many historically named tooth taxa like Paronychodon and Richardoestesia are today considered nomina dubia, and are used as form taxa to refer to isolated teeth from other localities displaced considerably in time and space from the type specimens. However, it is possible to refer isolated teeth to known taxa provided that the tooth morphology is known and the teeth originate from a similar time and place.

The ameloblastic fibro-odontoma (AFO) is essentially a benign tumor with the features characteristic of ameloblastic fibroma along with enamel and dentin. Though it is generally regarded as benign, there have been cases of its malignant transformation into ameloblastic fibrosarcoma and odontogenic sarcoma. Cahn LR and Blum T, believed in "maturation theory", which suggested that AFO was an intermediate stage and eventually developed during the period of tooth formation to a complex odontoma thus, being a hamartoma.

References

  1. ↑ Fraser GJ, Hulsey CD, Bloomquist RF, Uyesugi K, Manley NR, Streelman JT (February 2009). Jernvall J (ed.). "An Ancient Gene Network Is Co-opted for Teeth on Old and New Jaws". PLOS Biology. 7 (2): e31. doi: 10.1371/journal.pbio.1000031 . PMC   2637924 . PMID   19215146.
  2. ↑ Fraser GJ, Bloomquist RF, Streelman JT (2008). "A periodic pattern generator for dental diversity". BMC Biology. 6: 32. doi: 10.1186/1741-7007-6-32 . PMC   2496899 . PMID   18625062.
  3. ↑ "Sharks". www.ms-starship.com.
  4. ↑ Boyne PJ (1970). "Study of the chronologic development and eruption of teeth in elasmobranchs". Journal of Dental Research. 49 (3): 556–60. doi:10.1177/00220345700490031501. PMID   5269110. S2CID   34954175.
  5. ↑ Sasagawa I (June 1989). "The fine structure of initial mineralisation during tooth development in the gummy shark, Mustelus manazo, Elasmobranchia". Journal of Anatomy. 164: 175–87. PMC   1256608 . PMID   2606790.
  6. ↑ Michael E. Williams, Jaws: The early years, found here Archived 2016-03-24 at the Wayback Machine .
  7. ↑ Luan, X.; Ito, Y.; Diekwisch, T.G.H. (2005). "Evolution and development of Hertwig's epithelial root sheath". Developmental Dynamics. 235 (5): 1167–1180. doi:10.1002/dvdy.20674. PMC   2734338 . PMID   16450392.
  8. ↑ Frandson and Spurgeon, Anatomy and Physiology of Farm Animals., p. 305.
  9. ↑ Dassule HR, Lewis P, Bei M, Maas R, McMahon AP (November 2000). "Sonic hedgehog regulates growth and morphogenesis of the tooth". Development. 127 (22): 4775–85. doi:10.1242/dev.127.22.4775. PMID   11044393.
  10. ↑ Järvinen E, Salazar-Ciudad I, Birchmeier W, Taketo MM, Jernvall J, Thesleff I (December 2006). "Continuous tooth generation in mouse is induced by activated epithelial Wnt/β-catenin signaling". Proceedings of the National Academy of Sciences of the United States of America. 103 (49): 18627–32. Bibcode:2006PNAS..10318627J. doi: 10.1073/pnas.0607289103 . PMC   1693713 . PMID   17121988.
  11. ↑ Caceci. Veterinary Histology with subtitle "Digestive System: Oral Cavity" found here "EXERCISE 17: Oral Cavity". Archived from the original on 2006-04-30. Retrieved 2006-04-30..
  12. ↑ Fejerskov O (March 1979). "Human dentition and experimental animals". Journal of Dental Research. 58 (Spec Issue B): 725–34. doi:10.1177/002203457905800224011. PMID   105027. S2CID   9282056.
  13. ↑ Jake Andersen, DMD, Teeth
  14. ↑ "Teeth - Search View - MSN Encarta". October 29, 2009. Archived from the original on 2009-10-29.
  15. ↑ "Elephant Teeth". Elephant Facts. Retrieved 31 July 2020.
  16. ↑ "Class Mammalia, Order Tubulidentata, Family Orycteropodidae, Species Orycteropus afer," University of Michigan Museum of Zoology. Page accessed November 16, 2009.
  17. ↑ Hillson, Simon (2014). Tooth development in human evolution and bioarchaeology. New York. ISBN   978-1-107-01133-5. OCLC   863044047.{{cite book}}: CS1 maint: location missing publisher (link)
  18. 1 2 Kardong, Kenneth V. (1995). Vertebrates: comparative anatomy, function, evolution. McGraw-Hill. pp. 55, 57. ISBN   0-697-21991-7.
  19. ↑ "Ancylostoma duodenale". Nematode.net Genome Sequencing Center. Archived from the original on 2008-05-16. Retrieved 2009-10-27.
  20. 1 2 Richman, Joy M.; Handrigan, Gregory R. (April 2011). "Reptilian tooth development". Genesis. 49 (4): 247–260. doi: 10.1002/dvg.20721 . PMID   21309070.
  21. ↑ "SHH gene: MedlinePlus Genetics". medlineplus.gov. Retrieved 2021-04-06.
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