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teeth

teeth, hard, calcified structures embedded in the bone of the jaws of vertebrates that perform the primary function of mastication. Humans and most other mammals have a temporary set of teeth, the deciduous, or milk, teeth; in humans, they usually erupt between the 6th and 24th months. These number 20 in all: 2 central incisors, 2 lateral incisors, 2 canines, and 4 premolars in each jaw. At about six years of age, the preliminary teeth begin to be shed as the permanent set replaces them. The last of the permanent teeth (wisdom teeth) may not appear until the 25th year, and in some persons do not erupt at all. The permanent teeth generally number 32 in all: 4 incisors, 2 canines, 4 bicuspids, and 4 (or 6, if wisdom teeth develop) molars in each jaw. Human canines are the smallest found in any mammal.

Among all mammals, the tooth consists of a crown, the portion visible in the mouth, and one or more roots embedded in a gum socket. The portion of the gum surrounding the root, known as the periodontal membrane, cushions the tooth in its bony socket. The jawbone serves as a firm anchor for the root. The center of the crown is filled with soft, pulpy tissue containing blood vessels and nerves; this tissue extends to the tip of the root by means of a canal. Surrounding the pulp and making up the greater bulk of the tooth is a hard, bony substance, dentin. The root portion has an overlayer of cementum, while the crown portion has an additional layer of enamel, the hardest substance in the body. Most nonmammalian vertebrates do not have the outer layer of enamel on their teeth, but instead have a substance known as vitrodentine, similar to dentine, though much harder.

Proper diet is necessary for the development and maintenance of sound teeth, especially sufficient calcium, phosphorus, and vitamins D and C. The most common disorder that affects the teeth is dental caries (tooth decay). A widely accepted explanation of the process of tooth decay is that salivary bacteria convert carbohydrate particles in the mouth into lactic acid, which attacks the enamel, dentin, and, if left untreated, the pulp of the teeth. Regular cleansing and semiannual dental examinations (see dentistry) are important in preventing dental caries and gum disorders. Fluoridation of public water supplies and use of fluoride toothpastes also help prevent caries. In the study of fossil remains done in paleontology and physical anthropology, teeth are the most frequently found remains, a testament to their high mineral content and resistance to deterioration over time. See dentition.

Bibliography

See P. S. Ungar, Mammal Teeth: Origin, Evolution, and Diversity (2010).

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Tooth

One of the structures found in the mouth of most vertebrates which, in their most primitive form, were conical and were usually used for seizing, cutting up, or chewing food, or for all three of these purposes. The basic tissues that make up the vertebrate tooth are enamel, dentin, cementum, and pulp (see illustration).

Structure of a toothenlarge picture
Structure of a tooth

Enamel is the hardest tissue in the body because of the very high concentration, about 96%, of mineral salts. The remaining 4% is water and organic matter. The enamel has no nerve supply, although it is nourished to a very slight degree from the dentin it surrounds. The fine, microscopic hexagonal rods (prisms) of apatite which make up the enamel are held together by a cementing substance.

Dentin, a very bonelike tissue, makes up the bulk of a tooth, consisting of 70% of such inorganic material as calcium and phosphorus, and 30% of water and organic matter, principally collagen. The rich nerve supply makes dentin a highly sensitive tissue; this sensitivity serves no obvious physiological function.

Cement is a calcified tissue, a type of modified bone less hard than dentin, which fastens the roots of teeth to the alveolus, the bony socket into which the tooth is implanted. A miscellaneous tissue, consisting of nerves, fibrous tissue, lymph, and blood vessels, known as the pulp, occupies the cavity of the tooth surrounded by dentin.

The dentition of therian mammals, at least primitively, consists of four different kinds of teeth. The incisors (I) are usually used for nipping and grasping; the canines (C) serve for stabbing or piercing; the premolars (Pm) grasp, slice, or function as additional molars; and the molars (M) do the chewing, cutting, and grinding of the food. Primitively the placentals have 40 teeth and the marsupials 50.

In therian mammals, probably because of the intricacies and vital importance of tooth occlusion, only part of the first (or “milk”) dentition is replaced. This second, or permanent, dentition is made up of incisors, canines, and premolars; as a rule only one premolar is replaced in marsupials. Although the molars erupt late in development and are permanent, that is, not replaced, they are part of the first, or deciduous, dentition.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

tooth

One of a series of carved ornaments, typically a pyramidal shape or a four-petal flower, usually set in a concave molding band; used in the Romanesque and Gothic Revival styles. See also: Ornament
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved

tooth

[′tüth]
(anatomy)
One of the hard bony structures supported by the jaws in mammals and by other bones of the mouth and pharynx in lower vertebrates serving principally for prehension and mastication.
(design engineering)
One of the regular projections on the edge or face of a gear wheel.
An angular projection on a tool or other implement, such as a rake, saw, or comb.
(graphic arts)
The coarse or abrasive quality of a paper or a painting ground that assists in the application of charcoal, pastels, or paint.
A paper texture that holds ink more readily.
(invertebrate zoology)
Any of various sharp, horny, chitinous, or calcareous processes on or about any part of an invertebrate that functions like or resembles vertebrate jaws.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

tooth

1. In a paint film, a fine texture imparted either by pigments or by the abrasives used in sanding; this texture provides a good base for the adhesion of a subsequent coat of paint.
2. A dogtooth, 2.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

tooth

1. any of various bonelike structures set in the jaws of most vertebrates and modified, according to the species, for biting, tearing, or chewing
2. any of various similar structures in invertebrates, occurring in the mouth or alimentary canal
3. any of the various small indentations occurring on the margin of a leaf, petal, etc.
4. any one of a number of uniform projections on a gear, sprocket, rack, etc., by which drive is transmitted
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
'But this martial law that we are having now is actually a toothless martial law,' Lacson said, adding that: 'Inamin naman nila, pang-psywar lang talaga kung tutuusin.'
"How To Train Your Dragon: The Hidden World" follows Hiccup and Toothless on their latest exploits.
(Deakins remains credited as a visual consultant in "The Hidden World.") And the series deserves credit, too, for building a story -- adapted from Cressida Cowell's books -- around two unimpeded protagonists (Hiccup and Toothless) with prosthetic appendages.
When a big game dragon hunter called Grimmel threatens to kill Toothless and destroy Berk, Hiccup leads a quest to find the legendary hidden world of dragons.
A big game dragon hunter called Grimmel leads a vast fleet of ships and is determined to destroy their home and kill Toothless, as he is the last male of his breed of dragon.
The dazzling creature addition is something called a Light Fury, an alabaster-coloured dragon, whose non-domesticated allure (she's suspicious of humans) turns the normally intrepid Toothless into a hesitant suitor for her affections.
to It was proof of sport's toothless approach towards the issue of abuse
Instead of nabbing the so-called leaders who instigated the public, abused superior court judges and ridiculed the army chief, the toothless government is putting the blame on opposition workers for the havoc enacted.
Ruling Disy chief Averof Neophytou expressed optimism on Saturday that key bills necessary for the stability of the financial sector would be approved by parliament in its special session on Sunday but suggested that the opposition was trying to render certain provisions 'toothless' by submitting amendments.
However, Switzerland, who had looked toothless throughout the first half, got back on level terms five minutes into the second period when Zuber rose unmarked to head home a corner kick.
THREE seals found in distress and underweight made waves as they returned to the sea yesterday The mammals named Tristan, Toothless and Gilgamesh hit the surf again having been cared for in Courtown, Wexford, since last year.
He started the campaign with action from his homestead so that many others would see it as a serious business, in fact, the fear of EFCC then was the beginning of wisdom unlike now that it has become a toothless bulldog that cannot bite.