john hawks weblog

paleoanthropology, genetics and evolution

teeth

  • Tooth wear

    Sun, 2011-10-23 23:46 -- John Hawks
    Synopsis: 
    Laboratory exercise discussing the basics of dental attrition.

    Teeth have a close association with longevity. Enamel is the hardest substance in the body, but it does break, wear out, and is sometimes attacked by microbes. In Westernized contexts, we are all familiar with cavities, caused by acid-emitting bacteria in the mouth. But in many natural human societies, cavities (called caries) are rare. Instead, a lifetime of eating abrasive natural foods usually causes the teeth to wear down, a process called attrition.

    Dental attrition is very important in the anthropology of ancient peoples. It helps us to understand the food processing techniques — for example, the use of abrasive grinding stones to process grain in early agriculturalists. Dental wear also provides a way of understanding the ages at death of ancient skeletons. In Western societies, excessive tooth wear may be indicative of habitual behaviors such as grinding the teeth, or may result from biases in the chewing pattern to one side or part of the mouth.

    Differential wear describes a dentition in which one tooth is worn significantly more than its neighbors. A normal process of tooth wear results in differential wear, as first molars erupt at age 5 and develop many years of wear before the third molars erupt in the mid- to late teens.

    What to do: Examine the teeth at this station. How are they worn? Is there anything complicating their wear pattern, such as the presence of caries? Which individuals have differential wear? Which are worn the most?

    Study terms: 
    attrition
    tooth wear
    differential wear
    Tags: 
    teeth
    Anthropology 105
    development
    laboratory
    explainer

  • Deciduous teeth

    Mon, 2011-10-17 23:59 -- John Hawks
    Synopsis: 
    Laboratory exercise introducing eruption of deciduous dentition in humans and primates.

    Like most mammals, humans have two sets of teeth. The first set is called the deciduous dentition, but you probably know these as "baby teeth."

    The human deciduous dentition includes two incisors, one canine, and two molars in each quadrant. When people lose their deciduous molars, these are replaced by permanent premolars. The permanent molars do not have deciduous teeth in their places before them.

    Deciduous teeth are abbreviated with a "d" and the tooth type and number in lowercase. For example, the deciduous lower first molar is a dm1; the upper left deciduous canine is luc.

    What to do: Consider the series of models at this station. They represent the mandibular dentitions of children at different ages during their development. Can you determine the order that the permanent teeth erupt and replace the deciduous teeth? For example, are the permanent incisors the first to erupt? The permanent molars?

    Part 2

    There are several kinds of primate represented at this station. These primates have different adult body sizes, and grow at very different rates. Nevertheless, their teeth erupt in sequences that are very much like the human dental eruption sequence.

    Yet, there are exceptions. Many primates erupt their canine teeth relatively late in their eruption sequence. In humans, the upper canine typically erupts before the second molars. In many primates, the canine is delayed in development compared to the second molars.

    What to do: Examine the primate dentitions at this station. Identify the deciduous and permanent teeth that you see in each. Try to think about what age a human would likely be, with the same teeth present. Can you find aspects of tooth eruption that differ between humans and these primates?

    Study terms: 
    eruption
    deciduous
    Tags: 
    Anthropology 105
    explainer
    laboratory
    teeth
    development

  • Incisors

    Mon, 2011-10-17 23:41 -- John Hawks
    Synopsis: 
    Laboratory exercise introducing incisors, including lemur tooth combs.

    The incisors are the front teeth. They are basically flat and have a blade-like occlusal surface. Each quadrant has two incisors.

    In humans and other primates, the upper central incisor (called the I1) is typically larger, the lateral (the I2) smaller.

    At this station you'll find casts of several primates, including some prosimians with tooth combs. Examine these mandibles. Some of the tooth combs include four teeth, and some six. The tooth combs with six teeth include the two incisors (I1 and I2) and the lower canines. The four-tooth combs are missing either the lateral incisor or the canine. Specialists disagree on this point. What do you think?

    Study terms: 
    incisor
    canine
    lemur
    Tags: 
    Anthropology 105
    explainer
    laboratory
    teeth
    primates

  • Canines

    Mon, 2011-10-17 23:27 -- John Hawks
    Synopsis: 
    Lab exercise introducing canines, including sizes of maxillary canines in hominoids.

    The canine teeth in humans range from pointy-shaped to incisor-like in shape. There is only one canine in each quadrant, and it is the third tooth just distal to the incisors.

    Upper canines are often denoted UC and lower canines are then LC (so that the left lower canine is LLC.

    In many other primates, the canine teeth project out far beyond the others. There is often a large space, or \term{diastema} between the upper canine and the lateral incisor. For many species, the canine teeth are the largest difference between male and female skulls.

    This station has the skulls of several kinds of primates. Measure the height of the right canine tooth in each maxillary dentition. This measurement is taken from the tip of the canine to the base of its enamel.

    Then measure the breadth of the first molar.

    Your assignment is to make a plot showing how canine height relates to molar breadth in this sample of primates. Are there any outliers in your plot?

    Are there any other features of the mandibles that seem to correlate with canine breadth?

    Study terms: 
    canine
    mesial
    distal
    buccal
    lingual
    labial
    Tags: 
    Anthropology 105
    explainer
    laboratory
    teeth

  • Wisdom teeth

    Tue, 2011-10-11 08:12 -- John Hawks
    Synopsis: 
    Laboratory exercise to introduce third molar variation.

    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.

    Humans are not alone. Some other kinds of primates have entirely lost their third molars and normally erupt only two in each quadrant. The South American monkeys called callitrichids (marmosets and tamarins) are small-bodied monkeys who normally have only two molars in each quadrant of the jaw.

    Many people begin to develop third molars within their jaws, but the teeth never erupt. Others don't have any development of the third molars at all. We may not know about this unless we learn it from X-ray images. Sometimes teeth are extracted before they emerge from the jaw, or erupt, but typically any problems become apparent at or after eruption.

    We are interested in showing whether third molar eruption or extraction can be correlated with any of the measurements you took earlier in the semester. In the spreadsheet, for each of your third molars, indicate whether you have it in the tooth row now, whether it has been extracted, or whether it never erupted at all.

    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 a human who has never erupted her upper wisdom teeth, but who has the lower ones?

    Study terms: 
    wisdom teeth
    molar
    eruption
    callitrichid
    Tags: 
    Anthropology 105
    explainer
    laboratory
    teeth

  • 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

  • Incisors

    Sun, 2011-08-21 22:09 -- John Hawks
    Synopsis: 
    Description of upper and lower incisors with laboratory exercise.

    The incisors are the front teeth. They are basically flat and have a blade-like occlusal surface. Each quadrant has two incisors.

    In humans and other primates, the upper central incisor (called the I1 is typically larger, the lateral (the I2) smaller.

    The lower incisors are small, spatula-shaped teeth, with central (I1) and lateral (I2) incisors approximately the same size and shape in humans and most primates.

    What to do:

    At this station you'll find a series of casts of upper dentitions. Some of the incisors have ridges on their mesial and buccal edges, giving them the appearance of a scoop or shovel. These are called "shovel-shaped incisors." This is a trait that varies in human populations, and is more common in people of Asian or Native American ancestry. The casts at this station all represent individuals in a single Native American community in Alaska.

    Seriate these dentitions, in order of how shovel-shaped the central upper incisors appear to you. Once these are in the best order, consider: Does shovel-shaping of the lateral incisors (I2) go together with the central incisors?

    Study terms: 
    incisor
    lateral
    central
    shovel-shaped incisors
    Tags: 
    teaching
    explainer
    laboratory
    teeth

  • Teeth

    Sun, 2011-08-21 21:58 -- John Hawks
    Synopsis: 
    Overview of the laboratory goals for learning dental anatomy.

    Goals:

    • Learn about the types of permanent teeth, including incisors, canines, premolars, and molars.
    • Examine the shape of the dentition and learn some anatomical terms that relate to teeth, such as lingual, buccal, mesial and distal.
    • Find ways that some other primates differ in their dentitions compared to humans.
    Tags: 
    teeth
    teaching
    explainer
    laboratory

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Neandertals

For years, I've worked on their bones. Now I'm working on their genes. Read more about the science studying these ancient people.

Denisova

From a finger bone of an ancient human came the record of a completely unexpected population. My lab is working on the science of the Denisova genome.

Acceleration

The advent of agriculture caused natural selection to speed up greatly in humans. We're uncovering some of the ways that populations have rapidly changed during the last 10,000 years.

Malapa

Just outside Johannesburg, the Malapa site is producing some of the most exciting finds in human evolution. This site is the headquarters of the Malapa Soft Tissue Project.