Skeletal Series B: The Biological Basis of Teeth and Anatomical Directional Terms

As mentioned in the previous post teeth are a distinct part of human anatomy and are of special interest to the human osteologist in archaeological contexts.  Teeth are the most resistant skeletal element to chemical or physical destruction during burial of human remains and as such are often over represented in the archaeological record.  As the only skeletal element that directly interacts with the environment (via mastication of food) teeth are a vital source of knowledge on the age, sex and diet of individuals and past populations (White & Folkens 2005).  There is now an extensive academic research body of materials and articles available on the study of both hominin and archaeological teeth.

Teeth in situation in the maxilla (upper jaw) and mandible (lower jaw) of a Saxon skull.

Origin & Anatomy

Dentition is often found in the lower and upper jaw of most animals, and are thought to have developed originally from fish scales (White & Folkens 2005, Shubin 2008).  Teeth throughout the animal kingdom have different uses, and come in a variety of different shapes and sizes.  Homo sapiens (modern-day humans) have two sets of teeth throughout their life.  Each set is located in the Mandible & Maxilla, and often refered to as the ‘dental arches’ or dental arcades”.  The deciduous dentition appears during early infancy and consist of around 20 individual teeth.  The permanent dentition gradually replaces the deciduous dentition, and is normally complete by around around 18 to 20 years of age, with females possibly exhibiting earlier eruption rates.  Typically the wisdom teeth (the 3rd molars) are the last to erupt fully towards the end of adolescence (Mays 1998).

The permanent dentition consists normally of 32 teeth with 8 teeth in each quadrant of the mandibular and maxilla dental arcades, although care has to be taken when noting the number from archaeological examples as teeth can easily fall out of the sockets.

Here is a basic diagram of the inside of a normal healthy molar tooth.  As you can see the second diagram shows the basics again but also introduces the 4 different teeth that the human dentition is composed of.  Enamel is one of the hardest biological substances and the hardest in man and, alongside the dentine, provides the main cutting framework for each tooth.  Unlike human bone tissue, the tooth cannot regrow or repair damage.

Basic anatomical details of a generic molar tooth.

Enamel is almost entirely inorganic material, mostly hydroxyapatite arranged in think rods whilst the “dentine is around 75% inorganic material (again hydroxyapatite) with a mainly collagen organic component” (Mays 1998: 11).

The general anatomy of teeth alongside the 4 classes of teeth In the human (Homo sapiens) dentition.

Again, please click on the above diagram for the detail to be clear.

The four classes of teeth in the human dentition consist of the following (White & Folkens 2005):

1) Incisors (4 altogether, two to each quadrant).  The incisors are  flat and blade like, whose main job is to cut the food before mastication takes place.

2) Canines (4 altogether).  The canines are tusk-like and are conical in shape.  Their main job is to pinch and grab the food helping to bring it into the mouth for mastication.

3) Pre-Molars (4 altogether).  They are rounder and shorter than the canine crowns (see below for directional and anatomical terms) and usually have two cusps.  They are used primarily for grinding the food.

4) Molars (6 altogether).  The molars have crowns that are squarer, larger, and bear more cusps than any other tooth.  They are used , along with the pre-molars, for grinding and chewing the food to make it more palatable and easier for the stomach to digest.

Standard Anatomical Directional Terminology

Here are some basics terms for tooth terminology and anatomical positions based on the White & Folkens manual (2005):

The Mesial portion of the tooth is the closest to the central incisors (see above diagram). The Distal portion of the tooth is the opposite of Mesial.  The Lingual part of the tooth faces the tongue, whilst the Labial portion faces the lips, and is only used for the incisors and canines.  The term Bucccal is used for the opposite of Lingual, for the Pre-Molars and Molars.  The Interproxmial surfaces contact the adjacent teeth.  The biting surface of both dental arches is called the Occlusal Surface.  The root of the tooth is called the Apical.  The Crowns are the enamel tops of each tooth, whilst the Cusps are the bumps on the Pre-Molars and Molars.

Cambridge Manuals On Human Evolution on the anthropology of modern teeth, a great core guide to how human teeth are studied in archaeology.

This is a basic guide  from White & Folkens (2005), does not include the very specific terminology for the cusps on the molars.  A handy guide to the introduction and more in-depth use of teeth is the book above.  In the human dentition the teeth as a whole have been noted as being very similar in design (or homogenized) in comparison to other species whilst the morphological variation of each class of tooth (think canine, molar etc) has increased over on each of the teeth (White & Folkens 2005).  This seems like a contradiction in terms but human teeth are designed for an omnivorous diet, meaning that that  our dentition is designed to chew both plant and meat foods for our dietary requirements.

When the teeth are found in relative isolation they can be sided and matched with relative ease to either the maxilla or mandible portions of the human skull.  This can be done by noting the wear patterns on the crowns of each tooth and by looking at the size and root variation of the tooth.  Generally speaking males tend to have larger teeth than females, although there are idiosyncrasies present throughout human evolution (Jurmain et al 2011).  A later post will include talks on the palaeopathology of tooth disease and trauma.  In the meantime this guide should help in providing the basic information.

Until next time, keep smiling! (A. Boisei reconstruction pictured – notice the large teeth made for chewing tough fibrous plant material and flesh).

Bibliography

Jurmain, R. Kilgore, L. & Trevathan, W.  2011. Essentials of Physical Anthropology International Edition. London: Wadworth.

Mays, S. 1999. The Archaeology of Human Bones. Glasgow: Bell & Bain Ltd.

Schwartz, J. H. 2007. Skeleton Keys: An Introduction to Human Skeletal Morphology. New York: Oxford University Press.

Shubin, N. 2008.  Your Inner Fish: A Journey into the 3.5 Billion Year History of the Human Body. London: Pantheon.

White, T. & Folkens, P. 2005. The Human Bone Manual. London: Elsevier Academic Press.