Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Dentition
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
==Dental formula== Because every mammal's teeth are specialised for different functions, many mammal groups have lost the teeth that are not needed in their adaptation. Tooth form has also undergone evolutionary modification as a result of natural selection for specialised feeding or other adaptations. Over time, different mammal groups have evolved distinct dental features, both in the number and type of teeth and in the shape and size of the chewing surface.<ref name="Weiss&Mann1985p134"/> The number of teeth of each type is written as a dental formula for one side of the mouth, or [[Circular sector|quadrant]], with the upper and lower teeth shown on separate rows. The number of teeth in a mouth is twice that listed, as there are two sides. In each set, incisors (I) are indicated first, canines (C) second, premolars (P) third, and finally molars (M), giving I:C:P:M.<ref name="Weiss&Mann1985p134"/><ref name="CambridgeDictHumBiol&EvolDentalFormula"/> So for example, the formula 2.1.2.3 for upper teeth indicates 2 incisors, 1 canine, 2 premolars, and 3 molars on one side of the upper mouth. The deciduous dental formula is notated in lowercase lettering preceded by the letter d: for example: di:dc:dp.<ref name="CambridgeDictHumBiol&EvolDentalFormula"/> An animal's dentition for either deciduous or permanent teeth can thus be expressed as a dental formula, written in the form of a fraction, which can be written as {{DentalFormula|upper=I.C.P.M|lower=I.C.P.M}}, or I.C.P.M / I.C.P.M.<ref name="CambridgeDictHumBiol&EvolDentalFormula"/><ref name=Martin1983p102/> For example, the following formulae show the deciduous and usual permanent dentition of all [[Catarrhini|catarrhine primate]]s, including humans: #Deciduous: <math>(di^2\text{-}dc^1\text{-}dm^2) / (di_2\text{-}dc_1\text{-}dm_2) \times 2 =20.</math><ref name=Swindler2002/> This can also be written as {{DentalFormula|upper=di2.dc1.dm2|lower=di2.dc1.dm2}}. Superscript and subscript denote upper and lower jaw, i.e. do not indicate mathematical operations; the numbers are the count of the teeth of each type. The dashes (-) in the formula are likewise not mathematical operators, but spacers, meaning "to": for instance the human formula is {{DentalFormula|upper=2.1.2.2-3|lower=2.1.2.2-3}} meaning that people may have 2 or 3 molars on each side of each jaw. 'd' denotes deciduous teeth (i.e. milk or baby teeth); lower case also indicates temporary teeth. Another annotation is {{DentalFormula|upper=2.1.0.2|lower=2.1.0.2}}, ''if'' the fact that it pertains to deciduous teeth is clearly stated, per examples found in some texts such as ''The Cambridge Dictionary of Human Biology and Evolution.''<ref name="CambridgeDictHumBiol&EvolDentalFormula"/> #Permanent: <math>(I^2\text{-}C^1\text{-}P^2\text{-}M^3) / (I_2\text{-}C_1\text{-}P_2\text{-}M_3) \times 2 =32.</math><ref name=Swindler2002/> This can also be written as {{DentalFormula|upper=2.1.2.3|lower=2.1.2.3}}. When the upper and lower dental formulae are the same, some texts write the formula without a fraction (in this case, 2.1.2.3), on the implicit assumption that the reader will realise it must apply to both upper and lower quadrants. This is seen, for example, throughout ''The Cambridge Dictionary of Human Biology and Evolution''. The greatest number of teeth in any known [[placental]] land mammal{{specify|reason=which one?|date=January 2020}} was 48, with a formula of {{DentalFormula|upper=3.1.5.3|lower=3.1.5.3}}.<ref name="Weiss&Mann1985p134"/> However, no living placental mammal has this number. In extant placental mammals, the maximum dental formula is {{DentalFormula|upper=3.1.4.3|lower=3.1.4.3}} for pigs. Mammalian tooth counts are usually identical in the upper and lower jaws, but not always. For example, the [[aye-aye]] has a formula of {{DentalFormula|upper=1.0.1.3|lower=1.0.0.3}}, demonstrating the need for both upper and lower quadrant counts.<ref name="CambridgeDictHumBiol&EvolDentalFormula"/> ===Tooth naming discrepancies=== Teeth are numbered starting at 1 in each group. Thus the [[human]] teeth are I1, I2, C1, P3, P4, M1, M2, and M3.<ref name="CambridgeDictHumBiol&EvolDentalEruption"/> (See next paragraph for premolar naming etymology.) In humans, the third molar is known as the [[wisdom tooth]], whether or not it has erupted.<ref name=Harris1988p34/> Regarding premolars, there is disagreement regarding whether the third type of deciduous tooth is a premolar (the general consensus among mammalogists) or a molar (commonly held among human anatomists).<ref name="CambridgeDictHumBiol&Evolp135"/> There is thus some discrepancy between nomenclature in zoology and in dentistry. This is because the terms of human dentistry, which have generally prevailed over time, have not included mammalian dental evolutionary theory. There were originally four premolars in each quadrant of early mammalian jaws. However, all living primates have lost at least the first premolar. "Hence most of the [[prosimian]]s and [[platyrrhine]]s have three premolars. Some genera have also lost more than one. A second premolar has been lost in all catarrhines. The remaining permanent premolars are then properly identified as P2, P3 and P4 or P3 and P4; however, traditional dentistry refers to them as P1 and P2".<ref name=Swindler2002/> ===Dental eruption sequence=== The order in which teeth emerge through the gums is known as the '''dental eruption sequence'''. Rapidly developing anthropoid primates such as [[macaque]]s, [[Common chimpanzee|chimpanzee]]s, and [[australopithecine]]s have an eruption sequence of M1 I1 I2 M2 P3 P4 C M3, whereas [[anatomically modern humans]] have the sequence M1 I1 I2 C P3 P4 M2 M3. The later that tooth emergence begins, the earlier the anterior teeth (I1βP4) appear in the sequence.<ref name="CambridgeDictHumBiol&EvolDentalEruption"/>
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)