dentition

dentition, kind, number, and arrangement of the teeth of humans and other animals. During the course of evolution, teeth were derived from bony body scales similar to the placoid scales on the skin of modern sharks. Tooth structures such as those found in humans are restricted to certain vertebrates, i.e., most fish, mammals, and reptiles, and some amphibians. The teeth of sharks, which are primitive vertebrates, consist of simple conelike structures, sometimes with serrated edges and sometimes flattened for crushing shelled prey. In many lower vertebrates the individual teeth are replaced throughout the animal's life; old tooth loss and new tooth growth follow wavelike patterns down the length of jaw and affect alternate teeth at any one time, so that half the teeth in a region are always functional. Fish and reptiles that have teeth have homodont dentition; that is, all teeth are identical. The mammals have heterodont dentition, or teeth of different basic types, including incisors for nipping or cutting, canines for piercing, and premolars and molars for shearing and grinding. Carnivorous animals have relatively small incisors, used for grasping rather than for cutting; long and strong canines; and relatively thin, sharp premolars and molars, used for severing muscle and other tissues. Herbivorous animals have well-developed incisors, used to cut grass and other vegetation; canines that are either smaller than those of carnivores or absent altogether; and broad, flat premolars and molars for grinding food. In some herbivores, the upper canines are absent, so they cut vegetation by the combined action of the tongue and lower incisors. Omnivorous animals such as man have less specialized dentition. Only part of the dentition of mammals is usually replaced; however, the incisors of rodents grow out at the base as fast as they wear down at the tip. Teeth, the hardest structures in the body, have been well preserved as fossils and have played an important role for paleontologists and physical anthropologists in the study of human evolution.

Dentition is the development of teeth and their arrangement in the mouth.

All mammals except the monotremes, the edentates, the pangolins, and the cetaceans have up to four distinct types of teeth, with a maximum number for each. These are the incisor (cutting), the canine, the premolar, and the molar (grinding). Mammals that have distinct types of teeth are heterodont; others are homodont.

The number of teeth of each type is written as a dental formula for one side of the mouth, 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 are indicated first, canines second, premolars third, and finally molars. 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 dentition can be expressed as a dental formula. Teeth are numbered starting at 1 in each group, except the premolars which end at 4. This means that the carnassials are always the fourth upper premolar and the first lower molar. Thus the human teeth are I1, I2, C1, P3, P4, M1, M2, and M3. The human dental formula is:

Of cats it is:

The last upper premolar and first lower molar of the cat, since it is a carnivore, are called carnassials and are used to slice meat and skin. The armadillo, being homodont, has a dental formula that is simply 7/7.

The maximum dental formula for placental mammals is:

Non-placental mammals such as marsupials can have more teeth than placentals. The opossum's dental formula is:

In many mammals the children have a set of teeth that fall out and are replaced by adult teeth. These are called deciduous teeth, baby teeth or milk teeth. Animals that have two sets of teeth, one followed by the other, are said to be diphyodont. Normally the formula for milk teeth is the same as for adult teeth except that the premolars are missing.

The milk tooth formula for humans is:

The kitten has 26 teeth. See also: phalangeal formula.

Other uses: Dentition in archaeology

Dentition, or the study of teeth, is an important area of study for archaeologists, especially those specializing in the study of older remains. Dentition affords many advantages over studying the rest of the skeleton itself (osteometry). The structure and arrangement of teeth is constant and, although it is inherited, does not undergo extensive change during environmental change, dietary specializations, or alterations in use patterns. The rest of the skeleton is much more likely to exhibit change because of adaptation. Teeth also preserve better than bone, and so the sample of teeth available to archaeologists is much more extensive and therefore more representative.

Dentition is particularly useful in tracking ancient populations' movements, because, although all humans have the same basic 32 teeth, there are subtle differences in the shapes of incisors, the number of grooves on molars, and extra cusps on particular teeth. These differences can not only be associated with different populations across space, but also change over time so that the study of the characteristics of teeth could say which population one is dealing with, and at what point in that population's history they are.

References

Adovasio, J. M. and David Pedler. "The Peopling of North America." North American Archaeology. Blackwell Publishing, 2005. p. 35-36.

External links

• Colorado State's Dental Anatomy Page