Chapter 13 - Teeth as Cutting Tools

Abstract

Teeth are used to break off and break up food in order to increase the surface area before swallowing for the gut to finish the job by chemical action. They are arranged symmetrically along a jaw, locations being referenced within upper, lower, and left and right, quadrants. The tooth-bearing bones of the upper and lower jaws do not form a simple hinge and are what would be called linkages in engineering. They are highly mobile and are connected to the braincase only by ligaments and muscles, allowing the mouth to open to 150°. The sides of the lower jaws move independently of each other, alternately ratcheting prey into the throat. This intracranial bone mobility (cranial kinesis) exists in lizards and birds as well as snake. Teeth, like cutting tools, are designed not to break. When teeth are not replaced wear has to be avoided, if at all possible, for the teeth to function efficiently. Wearing out or loss of teeth can lead to death by starvation when a creature can neither feed nor defend itself. Mammalian teeth usually close upon one another, and different surfaces of a tooth that contact under normal load, or slide past surfaces of adjacent teeth during closing, determine the contact mechanics of teeth. Some contact surfaces are convex-to-convex, some concave-to-concave, and some convex-to-concave. The latter act like a pestle and mortar in breaking down food. The occlusal morphologies of teeth are categorized as primary and secondary.