Evening Republican, Volume 22, Number 144, Rensselaer, Jasper County, 19 June 1919 — All About Teeth [ARTICLE]

All About Teeth

(From the New* Bureau, Public Information Committee, American Museum of -> Natural History, New York City.)

There’s a new exhibit at the American Museum of Natural History that tells a great deal about teeth—about their structure, location, mode of implantation, growth and replacement, with special reference to the teeth of mammals. Many kinds of teeth are shown in the exhibit, frojn the curious, complicated apparatus called the “Aristotle’S lantern” in vogue among the sea-urchins to the great, cruel fang of the lion. The Aristotle’s lantern of the sea-urchin consists of five pyramidal jaws, each carrying a long, slender tooth of continu-oua-growth, which moves forward in the jaws as it becomes worn. away at the point. The horse-shoe king crab wears his teeth on his legs, at the first joints of which is a series of spines and sharp points. The food is torn to bits on these teeth and worked into the mouth opening. The lobster does his fletcherizing with teeth which are to be found on his fourth to ninth appendages. Some of these teeth are adapted to seizing the food, others to grinding it, etc. The exhibit also reveals the little-known fact that the beetle and worm boast teeth as useful and efficient as any. Of course there are teeth of many*kinds. But the typical tooth of a vertebrate or back-boned animal, as shown in cross-section, consists of (1) pulp contained in a cavity, which by deposition of lime in its exterior portion becomes (2) dentine, ivory or bone, forming the body of the tooth, (3) enamel, overlying the dentine on the crown of the tooth, and (4) cement, usually surrounding the base of. the tooth and sometimes covering part or all of the enamel of the crown. The teeth of some animals, however (the sperm whale, for example), have no enamel whatsoever. In man, as in most mammals, the teeth are set in distinct, separate sockets, called by the initiated “alveolas,” and are separated by a membrane from the surrounding bone. But nature has other ways of implanting teeth. The extihct sea reptile known to the scientist as Ichthyosaurus had his teeth planted in a continuous shallow groove, as w'as the habit with certain birds which lived many centuries ago. Modern birds, however, have adopted the fashion of going toothless. Another sort of attachment of the teeth is by means of a bony union of the outer side of the teeth with the inner side of the jaw. In a fourth case the base of the tooth is completely fused with the side of the jaw. It is another evidence of a beneficial nature that man, the only creature who is given to having his teeth extracted, does not have his teeth implanted in this last way. Bonn; miimals'lmvt; the advantage of teetli whicirare more or less movable, due to the fact that they are attached to the jaws by ligaments. This is the case with many fishes and some reptiles. With snakes this arrangement the swallowing of the food. Some animals, less fortunate than man, have only one set of teeth, which are expected to last them through an entire lifetime. Most animals, like man, have two sets —a temporary or milk set and a permanent "set. No mammal has more than two sets of teeth. Generally a tooth is replaced by the formation below it of another tooth. As the new tooth increases in size, the roots of the old one are absorbed until finally it falls out and gives place to the new. Most reptiles and fishes, however, are well supplied with teeth, having several series, which provides for a more or less continuous loss and replacement. The shark is not worried by the fear of a toothless old age, for he has several rows of teeth, one behind the other, and as fast as the teeth in the outer row are lost they are replaced by those just back of them. Replacement may be accomplished by the formation of a new tooth beside the old one which is absorbed at the point of contact until the developing tooth enters the base and replaces it. That is the wav crocodiles and lizards do it. Or teeth may be formed at the back of the series, these moving forward to take the place of those worn away. The teeth of the elephant are developed at the back of the jaw, and the entire row moves slowly forward, the front part of each tooth coming into use first and wearing away as It is pushed forward. While six teeth are developed on each side of either jaw, not more than parts of two teeth are in use at any one time.