Introduction to Teeth

Courtesy of WebMD

    We should first start out with a brief introduction to human teeth- the different types of teeth, their anatomy, and possibly a little on the physics involved in their eruption from the jaw bone.
    When researching the physics surrounding teeth, one should first understand their anatomy. As we can see from the illustration (picturing the left half of a bottom jaw) above, there are four basic types of teeth: incisors, canines, premolars, and molars. Each type of tooth has a different shape from the others and has its own special function in the process of breaking down food into a digestible state. What follows is a break-down of the special role each type of tooth plays in this process:

            Incisors: The incisors are the four front teeth found on both the top and bottom jaws (we have eight incisors in all). They are generally wide, flat teeth, specifically suited to their purpose of cutting through food. This forms the food into small portions that will be easily maneuverable inside one's mouth so that the other teeth can perform their functions in turn.

            Canines: There are four canine teeth, two on the top jaw and two on the bottom. They are situated on each side of the four incisors and are shaped with a sharp point. This form is ideally suited to their function of tearing food that is too tough to be simply cut with the incisors. This provides us with a method of ingesting food that is tougher than normal.

            Premolars: We have eight premolars in all. They are situated just beyond our canines, two on each side, and on both the top and bottom jaws. Their shape is somewhat broad, with ridges and indents; their function is to crush and grind food into very small pieces in preparation for digestion.

            Molars: People generally have at least eight molars in all, which are even broader than the premolars and have different ridge structures than the premolars as well. In this section, I include the third molars, which are commonly called "wisdom teeth". I state that people have "at least" eight molars due to the fact that not all people develop the third molars (which would give them twelve molars total). These teeth have a function similar to that of the premolars: they are used in the grinding and crushing of food. The molars are generally used for this purpose more often than the premolars.

    Before we discuss tooth eruption, here is  an illustration and brief definition for the different parts of a healthy tooth.

Courtesy of County Dental

        Enamel- perhaps the part of the tooth with which we are the most familiar, the enamel is the hard covering of the tooth above the gum line (the crown) and acts as the protective shield of the tooth, protecting it from decay.
        Dentin- a substance which is similar to bone in composition but is not as hard a substance as the enamel.
        Root of the Tooth- the portion of the tooth which lies below the gum line.
        Pulp Chamber- the chamber within the tooth which contains the soft tissue (the pulp) as well as the nerves and blood vessels of the tooth.
        Root Canals- two branches off of the pulp chamber within the tooth which lead down to the ends of the roots of the tooth and to the jaw bone. Nerves and veins are contained in these pathways as well.
        Root End Opening- openings in the ends of each root of a tooth through which the nerves and veins of the tooth exit the tooth, enter the bone of the jaw, and thereby connect to the rest of the nervous system.

    While I originally meant to be able to now provide greater insight into the physics involved in tooth eruption, I must admit that the sources I could find were quite limited, and I was unable to find a source which presented a single, unified view of what causes our teeth to erupt from the jaw bone. Instead, many of the web sites I visited provided differing theories on the "how and why" behind this process. 

    One thing that has been proven is this: that the dental follicle plays a large role in tooth eruption. The dental follicle being..."a loose connective tissue sac...interposed between the alveolar bone of the socket and the enamel organ of the unerupted tooth." (G.E. Wise and G.J. King). The theory is that this follicle plays a role in the break-down and building of bone around the erupting tooth. It can therefore cause the bone above where the tooth is sitting in the jaw to break down, opening the way for the tooth to move up through the bone. Here is where we begin the physics part of our presentation: the follicle can then tell the body to begin building up the bone underneath the new tooth, thereby applying an upward force on the underside of the tooth. This force applied to the tooth causes the tooth to apply a force of equal intensity, and opposite direction, on the new bone growth. This force propels the tooth upward through the gums. If this tooth is a permanent tooth, then as it moves upward through the gums, it will eventually contact and apply a force to the primary (or "baby") tooth that is in its future position. The primary tooth will apply an equal force on the new tooth, propelling itself out of the gum tissue.
    Judging by this particular theory, we can see that the eruption of teeth is, in the physics aspect, a matter of Sir Isaac Newton's Third Law of Motion, which states, "For every action force, there is an equal and opposite reaction force." (Giancoli)

Table of Contents

Title Page

Page 2: Tooth Correction

Page 3: The Physics of Chewing

Page 4: Tooth Facts