Biology Reference
In-Depth Information
maxilla and mandible and these numbers also differ between the primary and permanent
dentitions within species. Therefore, the notation appears as three or four numbers over three
or four numbers, for the primary (deciduous) and permanent dentitions of the maxilla and
mandible, respectively. The living primates have descended from a distant mammalian
ancestor that had a permanent dental formula of
3143
3143
. This means that this ancestor had 3
incisors, 1 canine, 4 premolars, and 3 molars per quadrant in their permanent dentition.
In order to compare “apples to apples” when discussing dental evolution, it is important
to make sure that like teeth are being compared with like teeth even if your study only
involves modern human dental material. Through the general trend of dental reduction in
the primate fossil record, it is clear to see that the third incisor and the first two premolars
have been lost over the course of primate evolution in the catarrhines (the taxon consisting
of Old World monkeys, apes, humans, and their ancestors). Thus, in the catarrhine primates,
the teeth are numbered as I1 (central incisor), I2 (lateral incisor), C (canine), P3 (first
premolar), P4 (second premolar), M1 (first molar), M2 (second molar), M3 (third molar) to
reflect the loss of the first two premolars from a distant primate ancestor.
The human primary dental formula is
212
212
while the human permanent dental formula is
2123
2123
. This means that humans have 2 incisors, 1 canine, and 2 molars per quadrant in their
primary dentition, and 2 incisors, 1 canine, 2 premolars, and 3 molars in their permanent
dentition.
TOOTH SIZE AND SHAPE
Descriptions of tooth form involve both measurements of the size and shape of the tooth
and its features as well as the appearance or absence of various traits. Because the tooth roots
are embedded in the maxilla and mandible during life, population and individual variation
in tooth crowns is the most well-documented aspect of tooth form although there is certainly
valuable variation to be studied in the tooth roots as well. For detailed descriptions of tooth
crown and root traits and their variation see Scott and Turner's The Anthropology of Modern
Human Teeth: Dental Morphology and its Variation in Recent Human Populations (1997).
Odontometrics
Measurements of the crown are frequently used to characterize size but can also be used to
construct indices that describe the shape of the tooth. The most commonly reported tooth
measurements are the mesiodistal and buccolingual distances of the tooth crown, which
represent the maximum length and breadth of the tooth crown, respectively (
Table 10.1
).
In humans, incisors are longer mesiodistally than buccolingually, canines tend to have nearly
equal values, and premolars and maxillary molars are larger in the buccolingual dimension.
Human mandibular molars are longer mesiodistally than they are wide buccolingually. The
conventional practice is to record and report measurements to the nearest 0.1 mm using
sliding dental calipers.
These basic measurements can then be used to calculate indices that are useful in
describing the overall shape and proportions of a given tooth (
Table 10.1
). For example,
