THE PERMANENT CANINE TEETH

Introduction/Morphology/Function/Location

Human canines are the longest and most stable of teeth in the dental arch. Only one tooth of this class is present in each quadrant. In traditional dental literature, canines are considered the cornerstones of the dental arch. They are the only teeth in the dentition with a single cusp. They are especially anchored as prehensile teeth in the group from whence they get their name, the Carnivora.

Maxillary canines by definition are the teeth in the maxilla distal, but closest to the incisors. Mandibular canines are those lower teeth that articulate with the mesial aspect of the upper canine.

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Maxillary Permanent Canine

Facial: The canine is approximately 1 mm narrower than the central incisor. Its mesial aspect resembles the adjacent lateral incisor; the distal aspect anticipates the first premolar proximal to it. The canine is slightly darker and more yellow in the color than the incisor teeth. The labial surface is smooth, with a well developed middle lobe extending the full length of the crown cervically from the cusp tip. The distal cusp ridge is longer than the mesial cusp ridge.

Lingual: Distinct mesial and distal marginal ridges, a well-devloped cingulum, and the cusp ridges form the boundries of the lingual surface. The prominent lingual ridge extends from the cusp tip to the cingulum, dividing the lingual surface into mesial and distal fossae.

Proximal: The mesial and distal aspects present a triangular outline. They resemble the incisors, but are more robust--especially in the cingulum region.

Incisal: The asymmetry of this tooth is readily apparent from this aspect. It usually thicker labiolingually than it is mesiodistally. The tip of the cusp is displaced labially and mesial to the central long axis of this tooth.

Right and Left: The distal surface is fuller and more convex than the mesial surface. The mesial contact point is at the junction of the incisal and middle third. Distally, the contact is situated more cervically. It is at the middle of the middle third.

Variation: Each of the major features of this tooth are 'variations on a theme.' In some persons, a cusp-like tubercle is found on the cingulum. Lingual pits occur only infrequently. On occasion, the root is unusually long or unusually short.

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Mandibular Permanent Canine

Facial: The mandibular canine is noticeably narrower mesidistally than the upper, but the root may be as long as that of the upper canine. In an individual person,the lower canine is often shorter than that of the upper canine. The mandibular canine is wider mesiodistally than either lower incisor. A distinctive feature is the nearly straight outline of the mesial aspect of the crown and root. When the tooth is unworn, the mesial cusp ridge appears as a sort of 'shoulder' on the tooth. The mesial cusp ridge is much shorter than the distal cusp ridge.

Lingual: The marginal ridges and cingulum are less prominent than those of the maxillary canine. The lingual surface is smooth and regular. The lingual ridge, if present, is usually rather subtle in its expression.

Proximal: The mesial and distal aspects present a triangular outline. The cingulum as noted is less well developed. When the crown and root are viewed from the proximal, this tooth uniquely presents a crescent-like profile similar to a cashew nut.

Incisal: The mesiodistal dimension is clearly less than the labiolingual dimension. The mesial and distal 'halves' of the tooth are more identical than the upper canine from this perspective. You will recall that the cusp tip of the maxillary canine is facial to a ling through the long axis. In the mandibular canine, the unworn incisal edge is on the line through the long axis of this tooth.

Variation: One variation of this tooth has captured the attention of board examiners. It is this: On occasion, the root is bifurcated near its tip. The double root may, or may not be accompanied by deep depressions in the root.

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Comparative Anatomy: Canines of Interest in other Species

In mammals, canines are single rooted teeth adapted for tearing food. They are often the largest teeth in the mouth. In humans they are much reduced in size. This condition permits the side-to-side motion in the human chewing cycle. In many species canines project well beyond the level of the other teeth and may interlock when the teeth are closed (preventing side-to-side motion).

Rodents don't have canines at all. The tusks of the wart hog, barbirussa, and the extinct sabre tooth cat are canines of dramatically increased size. The most typical offensive specialization in mammalian teeth is represented by the canines.

1. Smilodon, the saber-tooth cat is now extinct. Well known from La Brea in Los Angeles County, this spectacular animal had continuous growing maxillary incisors over 6 inches in length. This carnivore died out 10,000 years ago and may have been encountered by the First Americans who came from Siberia. The tusk-like canines were probably used to attack large, thick-skinned animals such as the mammoth and giant sloth.

2. The walrus, a pinneped related to seals and sea lions, lives on a specialized diet of shellfish. All of its teeth are reduced to blunt, cone-like structures except for the tusk-like continuously growing canines. They are used to scoop up seaweed and for locomotion on ice when out of the water.

 

3. Baboons and sexual dimorphism. Among many animals, the tusk-like development of canines is a much more predominate feature in the male animal than in the female. Examples are the pigs, deer, baboons, and the anthropoid apes. In many animals, the larger and stronger tusks of the male animals are used in fighting--often the combat for exclusive access to females. Baboons use them for threatening displays; as such, canines are 'social teeth.'

Horses present an unusual dental sexual dimorphism: in females, the already reduced canines may be rudimentary or may be absent altogether.

4. The pig family present highly developed weapon teeth. In wild pigs, the canines are huge tusks projecting outside the mouth cavity, which continue to grow and erupt throughout life.

The male wart hog (the wild boar), has canines of the upper jaw that may turn upward and attain a length of 8 to 10 inches. They are used for digging roots and as formidable weapons in combat. In the Hebrides Islands, aboriginal peoples will break out the upper canines, causing the lower ones to grow into fanciful spirals that are used for ornamental purposes.

Even more intimidating is the babirussa, the wild pig of Malayia. It has upturned canines in the upper jaw that are actual extraoral teeth that grow up through the roof of the snout. The teeth sweep back to the forehead, sometimes attaining a length of seventeen inches. These remarkable teeth in the male are probably sexual ornaments; in the female, they are mere nubs.

..... CJ '98

Resources:

Berkovitz, B., Holland, G. and Moxham, B. Oral Anatomy 2nd ed. St. Louis: Mosby Year Book, 1992.

Jordan, R., Abrams, L., and Kraus, B. Kraus' Dental Anatomy and Occlusion 2nd ed. St. Louis: Mosby Year Book, 1992.

Krause, B . and Jordan, R. The Human Dentition Before Birth. Philadelphia: Lea & Febiger, 1965.

Peyer, B. Comparative Odontology. Chicago: University of Chicago Press, 1968.

Ripley, D. ed. Tropical Asia. New York: Time, Inc. , 1964.

Scott, J. and Symons, N. Introduction to Dental Anatomy 7th ed. London: Chirchill Livingstone, 1974.