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Teeth

Other Terms: Teeth, Teeth set, Set of teeth, Dentes, Dents

Embryology

In normal development two sets of teeth will form: the first set is referred to as the primary dentition or the deciduous teeth, and the next is the secondary dentition or the primary teeth. Teeth are derivatives of the integument and arise from ectoderm, mesenchyme, and neural crest cells. The ectoderm within the oral cavity gives rise to the enamel, and the rest of the teeth arise from neural crest and surrounding mesenchyme.

Adult Anatomy

The primary function of the teeth is mastication, which is the process of breaking down tough tissues and plant fibers by chewing. This aids in the saturation of these materials with saliva and some enzymes including salivary amylase. Upon making a vertical section through a tooth a cavity will be found in the interior of the crown and the center of each root. The cavity opens by a minute orifice at the base of each root called the apical foramen. This space is referred to as the pulp cavity, which contains a highly vascular loose connective tissue. The vessels and nerve enter the tooth via the apical foramen which is located at the point of each root. The solid portion of the tooth consists of three structures: the exposed covering of a tooth is the enamel which is composed of a very dense calcium phosphate substance, which is the hardest biologically manufactured substance. Next the dentin, which forms the bulk of the tooth, is a modification of osseous tissue. The primary difference is that unlike bone the dentin contains no living cells. Instead it contains dental canaliculi which are cytoplasmic processes that are arranged parallel to one another, and open at their inner ends into pulp cavity. The last solid portion is called the cement, which is a thin layer on the roots of the teeth, from the termination of the enamel to the apex of each root where it is often much thicker. This tissue is very similar to most bone tissue.

General Information

There are four classes of teeth, molars, pre-molars, canines, and incisors. Each tooth has three portions: the crown which projects above the gums, the root is imbedded in the maxilla or mandible, and the neck is the constricted portion between the crown and root. The incisors are named for the sharp cutting edge. There are eight incisors, which form the four front teeth in each dental arch. The crown is directed vertically, and is chisel-shaped. The labial surface is convex, smooth, and highly polished. The lingual surface is concave and often has an inverted V-shape eminence situated near the gum. The neck is constricted. The root is long, single, conical, transversely flattened, and slightly grooved on either side in the longitudinal direction. The canines are four in number, two in the upper, two in the lower arch, one being just lateral to each lateral incisor. The crown is large and conical. The labial surface is very convex. The lingual surface is a little hollowed and uneven. It then tapers to a blunted point or cusp, which projects beyond the level of the other teeth. The root is single, but longer and thicker than that of the incisors, conical in form, compressed laterally, and marked by a slight groove on each side. There are eight premolars, four in each arch. They are situated lateral to and behind the canine teeth. They are small and shorter than the canine teeth. The crown of the premolars is compressed anteroposteriorly. They are surmounted by two pyramidal eminences, a labial and a lingual. These eminences are separated by a groove. Of the two emionences, the labial is the larger and more prominent. The neck is oval. The root is generally single, compressed, and presents in front and behind a deep groove. The apex is generally bifid. The molars are the largest of the permanent set. Their broad crowns are adapted for grinding and pounding the food. There are twelve of them: six in each arch. Three are posterior to each of the second premolars. The crown of each is nearly cubical in form. They are convex on their buccal and lingual surfaces. The crowns are flattened on their surfaces of contact and surmounted by four or five cusps. These cusps are separated from each other by a crucial depression. The neck is distinct, large, and rounded. The upper molars have three roots while the lower molars have only two roots. Deciduous Teeth (20) Molars Canines Incisors Incisors Canines Molars Upper Jaw 2 1 2 2 1 2 Lower Jaw 2 1 2 2 1 2 Permanent Teeth (32) Molars Premolars Canines Incisors Incisors Canines Premolars Molars Upper Jaw 3 2 1 2 2 1 2 3 Lower Jaw 3 2 1 2 2 1 2 3 Spanish: Dientes German: Zähne French: Dents Italian: Denti

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