I. INTRODUCTION: HUMANS AND OTHER MEMBERS OF THE ANIMAL KINGDOM
In dentistry, teeth are recognized for their importance in chewing of food, attractiveness, and speech. Teeth have also have many paramasticatory functions such as tools in the preparation of leather, holding tacks when upholstering furniture, or toying with a cigarette holder.
Humans have two sets of teeth, they erupt vertically, and dental difference between males and females are small. In this article we explore the range of variation beyond routine human dental form and function.
II. TERMS USED IN COMPARATIVE DENTAL ANATOMY AND DENTAL ANTHROPOLOGY
Some of the terms here are familiar to the dental practitioner; they are included here for the benefit of persons not trained in clinical dentistry.
The first three sections below will be familiar territory for the dental practitioner. Terms used in non-clinical dental literature will have their Greek or Latin derivation explained for ease in learning.
Teaching a unit on terms can be deadly in the classroom. Its inclusion here is intended to do the following:
(1) Introduce the reader to another dimension in dental terminology; and
(2) Illustrate the variability of teeth beyond the condition seen in humans.
A. Terms of Location
Teeth can be described by their attachment to the maxilla or mandible, thus the terms maxillary or mandibular to describe these teeth. Dental practitioners often say upper or lower in clinical practice. Teeth toward the midline are anterior; teeth away from the midline are posterior. Incisors and canines collectively are anterior teeth. Premolars and molars collectively are posterior or cheek teeth.
B. Categories of Teeth by Shape
When teeth are uniformly of similar shape in a dentition, it is described as homodont. In a heterodont dentition, teeth are regionally specialized into classes.
C. Categories of Teeth by Generation
A monophyodont dentition has a single generation of teeth is. The condition of having just two generations of teeth as in humans is called diphyodont. Many generations of teeth as seen in many reptiles are described as apolyphyodont dentition.
D. Crown Form
Bunodont (Gr = mound or hill) teeth have cone-shaped tubercles or cones; they are low crowned with well-developed roots. An example is the posterior teeth in the pig.
Selenodont (Gr = the moon) teeth have cusps transformed into half-moon shapes. The teeth themselves are elongated anterposteriorly. The concave side faces laterally in the upper jaw; lingually in the lower jaw. The grinding stroke is thus from the outside inward and from the inside outward. An example is in the cheek teeth of sheep.
Sectorial (L = secare to cut) teeth are blade-like teeth adapted to cutting the diet into pieces and swallowing them whole. A specialized variant in carnivores are the carnassials which consist of the last premolar in the upper jaw and the first molar of the lower jaw.
Maxillary and mandibular carnasial teeth
From left to right: dog, cat, and the bear
Lophodont (Gr = crest) molars are ridged teeth that have transverse ridges as in the tapir. (My note: lophs are sharp crests that join cusps in multicusped teeth. Dentists would identify those crests as transverse ridges.)
Bilophodont molars have two sets of transverse ridges.
Polylophodont molars have many ridges as seen in the elephant molar. The power stroke is where the lower molars slide forward against the upper molars.
Brachydont (Gr = short) teeth have low crowns and well-developed roots. This condition is seen in humans.
Hypsodont (Gr = height) teeth have long crowns and short roots as seen in the horse. It them, it is a function adaptation for continuous wear sustained by chewing grass with a high abrasive silica content.
Haplodont (Gr = simple) teeth have simple crowns and roots, as seen in the dolphin.
Tusks are incisors or canines of continuous growth that protrude beyond the lips when the mouth is closed. They include the following:
(1) The incisors of the Elephant and Hippopotamus;
(2) The left incisor of the Narwhal;
(3) Canines of the Wild Boar;
(4) Sus babirussa;
(5) Wart Hog; and
(6) The Walrus.
(My note: this list is not exhaustive. Consult the resources listed at the end of this article for additional references.)
III. CLASSES OF TEETH
How do you classify teeth in heterodont dentitions? The following applies to the majority of mammalian teeth.
Incisors are maxillary teeth located in the premaxilla (or a comparable position in the maxilla as in humans). The mandibular incisors are those teeth that articulate with the maxillary incisors.
Canines are maxillary teeth that are the first in the tooth row past the premaxillary suture (distal to the incisor farthest from the midline). The mandibular canine is the tooth that articulates directly mesial from the maxillary canine.
Premolars are cheek teeth preceded by deciduous molars and are located anterior to the molars,
Molars are cheek teeth without deciduous predecessors.
Berkovitz, B., Holland, G., and Moxham, B. Color Atlas and Textbook of Oral Anatomy Histology and Embryology 2nd ed. St. Louis: Mosby Year Book, 1992.
Hillson, S. Teeth New York: Cambridge University Press, 1996.
Jordan, R., Abrams, L, and Kraus, B. Kraus' Dental Anatomy and Occlusion 2nd ed. St. Louis: Mosby Year Book, 1992.
Peyer, B. Comparative Odontology. Chicago: The University of Chicago Press, 1968.
Ripley, D. ed. Tropical Asia. New York: Time Inc., 1964.
Scott, J. and Symons, N. Introduction to Dental Anatomy 8th ed. Edinborough: Churchill Livingstone, 1977.
Swindler, D. Dentition of Living Primates. New York: Academic Press, 1976.
Widdowson, T. Special or Dental Anatomy and Physiology and Dental Histology Vol II, 7th ed. London: Staples Press Ltd., 1946.