Anthropology 105

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?

The long bones grow in parts. Early in fetal development, the bones are formed from cartilage. Bone tissue forms as special cells (called osteoblasts) lay down mineralized channels into the cartilage. Initially, the shafts, or diaphyses of the long bones begin to ossify. Later, the articular ends of the bone form their own centers of ossification, called epiphyses. Between the diaphysis and epiphyses remains a thin plate of cartilage, called the metaphysis.

As the bone grows, the metaphysis constantly adds new cartilage, and the diaphysis continues to ossify into this cartilage. So the bone can grow even as parts of it have already become mineralized tissue.

During the course of development, the bone tissue is recycled, gradually altering its shape. The hard cortical tissue can be invaded by cells that destroy the bone, called osteoclasts, only to have new bone laid down by secondary osteoblasts. The surface of the bone can be altered by having bone gradually removed, a process called resorption. Thus, bones remain living organs that can change their shape gradually, heal themselves, and adapt to new habits and needs.

What to do: This station has many juvenile bones, including a model skeleton of a young child. Try to identify the shafts of the long bones.

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?

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?