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Medicine LibreTexts

6.8: Dentition

  • Page ID
    13065
  • Two parts make up the structure of teeth: a portion within the mouth called the crown, and a portion within the jaw called the root. The outer surface of the crown seen in the mouth is a card white substance called enamel. Directly beneath the enamel is a softer material called dentine. The central portion of the root contains the pulp or nerve bundle feeding the tooth, called the pulp chamber. The root itself is made of dentine and is covered on the outside with a protective substance called dentine.

    Observe the crowns of the teeth as seen while in the jaw. Note that the number of teeth is the same in both the upper and lower jaw. There are four types of teeth present in the upper and lower jaw: 4 incisors, 2 canines, 4 premolars, and 6 molars for a total of 32 teeth. For comparative purposes in the study of evolutionary change, it is customary to represent the dentition by the number of teeth in each quadrant of the mouth, as 2.1.2.3.

    The incisors are generally chisel-shaped, though some persons including most American Indians many have lateral ridges making them shovel-shaped (particularly the upper incisors). The upper incisors are generally wider than the lowers. The canines are more massive than incisors and when unworn are slightly projecting and pointed. Due to the narrowness of the lower incisors the lower canine usually occuldes slightly forward of the upper one. The premolar or bicuspid teeth are distinguished by 2 cusps, one lingual (on the tongue side) and one buccal (on the cheek side). In the molar teeth a distinction may be made between uppers and lowers. The lower molars are square or rectangular in shape, with 4 - 5 cusps. The more anterior of these are generally larger decreasing posteriorly and have more complicated cusp pattern. The upper molars are in general smaller than the lowers, and also decrease in size posteriorly. Three to four cusps are generally seen in the upper molars; if three are present, two will be on the buccal side and one on the lingual. In addition, the outline of the upper molar tends to be slightly oblique rather the rectilinear as in the lowers.

    Roots of the teeth are also helpful in determining if they are uppers/lowers and siding. The roots of the incisors and canines are single, rounded and tapering, often curved at the ends. That of the canine is considerably longer and stouter than those of the incisors. The roots of the premolars are wider and tend to be grooved in a fashion which indicates an incipient tendency to be divided into a lingual and buccal root. The roots of the molar teeth are quite distinct as between the upper and lower. The roots of the lower molars are double, having an anterior and posterior component, each generally grooved like the root of a premolar. The third lower molar generally has all parts of the root fused and somewhat curved. The typical root pattern of the upper molar is two distinct roots on the buccal side and one on the lingual side. In the second upper molar the three roots are often less widely spread than in the first, and in the third a single massive fused root is found. Individual variations make it difficult to identify loose molars exactly.

    Many types of variation, often involving accessory cusps are found. Occasionally deciduous teeth will be encountered. In addition to having smaller crowns, deciduous teeth are recognized by the thinness and wide divergence of the molar roots.

    Teeth of non-industrial peoples are often deeply worn, as more processing of food occurs within the mouth. The type of wear seen in the dentition and the kind of pathology present give an indication of the diet and the cultural habits of the individual. Microscopic study of sections taken through the teeth can provide additional information about the individual’s health and nutritional status.

    Terms

    Buccal - The surfaces of the premolars and molars facing toward the cheek.

    Cusp - A protubance on the grinding surface of the canine, pre-molar, or molar.

    Distal - The tooth surface farthest from the median line of the dental arch (posterior aspect).

    Incisal edge - The cutting edge of an incisor.

    Labial - The surfaces of the incisors and canines facing toward the lips.

    Lingual - The tooth surfaces facing toward the tongue.

    Mesial - The tooth surface closest to the median line of the dental arch (anterior aspect).

    Occlusal surface - The bitting or grinding surface of a tooth.

    Ridge - A linear elevation on a tooth surface.

    Screenshot (171).png

    Maxillary Dentition

    Top - Central Incisor. Middle - Lateral Incisor. Bottom - Canine.

    Screenshot (172).png

    Mandibular Dentition

    Top - Central Incisor. Middle - Lateral Incisor. Bottom - Canine.

    Screenshot (173).png

    Top - Maxillary Premolar 1 Top - Mandibular Premolar 1

    Middle - Maxillary Premolar 2 Middle Mandibular Premolar 2

    Bottom - Maxillary Molar 1 Bottom - Maxillary Molar 1

    Screenshot (174).png

    Top - Upper Molars 2 & 3 Bottom - Lower Molars 2 & 3

    Dental Variation

    Carabelli's cusp - Additional cusp on the mesio-lingual border of the upper molars. Seen at the highest frequency among those of European descent. (Hillson 1996)

    Enamel extension - Found on teeth with multiple roots, enamel extends down the root. Most commonly found in upper premolars and molars. (Hillson 1996)

    Enamel pearl - Found in association with enamel extensions, except the enamel forms a small nodule. Most sommonly found in upper second and third molars. (Hillson 1996)

    Shovel-shaped incisors - The marginal ridges on the lingual aspect of the incisor are prominent with a deep central fossa. If on the lingua and labial surface this is termed dourble shoveling.

    Supernumerary - Additional teeth, may be seen at multiple locations within the maxillary or mandibular alveoli. These teeth may be peg shaped.

    For more information on non-metric dental variation see Hillson's (1996) Dental Anthropology or Turner et al. (1991) for an introduction to the series of dental casts of several non-metric traits available through Arizona State University.

    Dental Pathology

    Abscess - Cavitations in the bone surrounding the tooth root, resulting in the loss of a tooth and eventually absorption of the bone.

    Caries - Destruction of one of the three dental structure (enamel, dentine, or cementum), caused by bacteria in the mouth. These may be located on the occlusal surface, smooth surface, wtihin the pulp chamber, at the cemento-enamel junction, or on the root. May be seen as a brown spot in the early phase, followed by creation of a cavity within the affected structure.

    Dental enamel hypoplasia - Defect in the enamel of the tooth caused due to developmental issues during secretion of the structure. May cause bands of varying thickness around the circumference of the tooth; also seen in the form of pitting. thought to be associated with a number of physiological stressors including but not limited to malnutrition, parasites, and weaning.

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