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paleoanthropology, genetics and evolution

dental formula

  • Molars

    Tue, 2011-10-11 08:01 -- John Hawks
    Synopsis: 
    Laboratory exercise to introduce the terminology and anatomy of the molars.

    The most distal teeth are molars. Most humans have three molars, but many — especially in America — have their third molars (called wisdom teeth) extracted. Some people do not develop third molars at all, or they never erupt into occlusion. Molars have three or more cusps, and are used as grinding teeth.

    The upper molars are typically labeled with superscript numbers M1, M2, and M3, the lowers with subscript numbers M1, M2 and M3. Hence, the left lower first molar becomes LM1.

    Teeth have different directional terminology, referring specifically to the tooth row and the mouth. The direction toward the center front of the tooth row is mesial, and toward the rear of the tooth row is distal. For molars and premolars, the direction toward the cheek is buccal, and in toward the tongue is lingual.

    The two incisors, one canine, two premolars and three molars on both top and bottom are called the human dental formula. We write a dental formula as follows:

    2 1 2 3
    ___________
    2 1 2 3
    Study terms: 
    molar
    distal
    mesial
    buccal
    lingual
    dental formula
    Tags: 
    Anthropology 105
    explainer
    laboratory
    anatomy
    teeth

  • Premolars in primates

    Tue, 2011-10-11 07:53 -- John Hawks
    Synopsis: 
    Laboratory exercise introducing the different premolar numbers in different kinds of primates.

    Different kinds of primates have different numbers of premolars in their dentitions. The ancestral number of premolars in primates is three in each quadrant of the jaw. From this ancestral number, the common ancestors of the Old World monkeys, apes and humans lost their most mesial premolars, the P2 and P2. That leaves us only two premolars where many primates have three.

    The last common ancestor of the primates had three premolars in each quadrant. Four superfamilies, including lemuroids (lemurs), lorisoids (lorises and galagos), tarsioids (tarsiers) and ceboids (New World monkeys), still have members with the ancestral three premolars. Lemurs are variable today, as some species have lost one of the premolars. Hominoids (apes and humans) and cercopithecoids (Old World monkeys) evolved from a common ancestor that had also lost its premolars. These two superfamilies belong to the group called the Catarrhini, so that we are catarrhine primates as well as hominoids.

    Additionally, the anatomy of the premolars can vary. Many catarrhines have lower P3 with a single, large cusp. Some of them have a cutting edge running from the cusp mesially (toward the front). This acts in a scissor-action against the upper canine, and is called a sectorial P3. In species with three premolars, many have a sectorial P2 instead.

    At this station, there are some primates with different kinds of premolars. Is there any way of predicting which primates have three premolars in each quadrant? What determines whether the mandible has a sectorial P3?

    The two incisors, one canine, two premolars and three molars on both top and bottom are called the human dental formula. We write a dental formula as follows:

    2 1 2 3
    ___________
    2 1 2 3

    What is the dental formula of primates who have three premolars in each quadrant?

    Study terms: 
    sectorial
    premolar
    dental formula
    Ceboidea
    Hominoidea
    Cercopithecoidea
    Tarsioidea
    Lemuroidea
    Lorisoidea
    Catarrhini
    Tags: 
    Anthropology 105
    anatomy
    teeth
    explainer
    laboratory

  • Premolars

    Tue, 2011-10-11 07:37 -- John Hawks
    Synopsis: 
    Laboratory exercise to familiarize students with premolars in the dentition.

    The premolars are directly distal to (behind) the canines. Generally there are two premolars in each quadrant. Counting backward from the front of the jaw, there are normally two adult incisors, one canine, and then the two premolars, making them the fourth and fifth teeth in each row.

    In anthropology, we number these teeth differently from dentists, because the premolars in humans are homologous with the distal premolars in other mammals. So the human premolars are called the third and fourth premolars, even though we have only two of them! The lowers are numbered P3 and P4; the uppers P3 and P4.

    Premolars usually have two distinct points, or cusps, on their occlusal surface. In humans the lower third premolar is sometimes shaped very much like a canine tooth with only one cusp. In many primates, the P3 has only one large cusp that cuts against the distal edge of the upper canine, like a scissors.

    Examine the premolars at this station, both upper and lower. Learn to distinguish these from the other teeth.

    The two incisors, one canine, two premolars and three molars on both top and bottom are called the human dental formula. We write a dental formula as follows:

    2 1 2 3
    ___________
    2 1 2 3
    Study terms: 
    premolar
    distal
    mesial
    dental formula
    cusp
    Tags: 
    Anthropology 105
    explainer
    laboratory
    anatomy
    teeth
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