Part 15 (1/2)

PHYSIOLOGY OF THE TEETH.

219. The use of the teeth is twofold. 1st. By the action of the incisors the food is divided, while the molars grind or break down the more solid portions of it. By these processes, the food is prepared to pa.s.s more easily and rapidly into the stomach.

220. In the mastication of food there are two movements of the lower jaw--the action by which the teeth are brought together, and the lateral motion. In the former, the food is cut or divided, the jaws acting like shears. This movement is produced by the action of two large muscles situated on each side of the head and face.

_Observation._ The muscles attached to the lower jaw are of great strength; by their action alone, some persons are enabled to bite the hardest substances. By putting the fingers upon the side of the head above and in front of the ears, and upon the face above the angle of the jaw, while masticating food, the alternate swelling and relaxation of these muscles will be clearly felt.

221. The lateral, or grinding movement of the teeth, is produced by the action of a strong muscle that is attached to the lower jaw on the inside.

_Observation._ Those animals that live solely on flesh, have only the cutting, or shear-like movement of the jaws. Those that use vegetables for food, have the grinding motion; while man has both the cutting and grinding movement.

219-222. _Give the physiology of the teeth._ 219. Give one of the functions of the teeth. 220. How many movements of the lower jaw in masticating food? What effect has the first movement upon the food?

How produced? What is the character of the masticating muscles? 221.

How is the grinding motion of the teeth produced? What is said of the movements of the teeth in different animals?

222. 2d. The teeth aid us in articulating with distinctness certain letters and words. An individual who has lost his front teeth cannot enunciate distinctly certain letters called dental. Again, as the alveolar processes are removed by absorption soon after the removal of the teeth, the lips and cheeks do not retain their former full position, thus marring, in no slight degree, the symmetry of the lower part of the face. Consequently, those simple observances that tend to the preservation of the teeth are of great practical interest to all persons.

HYGIENE OF THE TEETH.

223. _To preserve the teeth, they must be kept clean._ After eating food, they should be cleansed with a brush and water, or rubbed with a piece of soft flannel, to prevent the _tartar_ collecting, and to remove the pieces of food that may have lodged between them.

Toothpicks may be useful in removing any particles inaccessible to the brush. They may be made of bone, ivory, or the common goose-quill.

Metallic toothpicks should not be used, as they injure the enamel.

224. _The mouth should be cleansed with pure tepid water at night, as well as in the morning_; after which the teeth should be brushed upward and downward, both on the posterior and anterior surfaces. It may be beneficial to use refined soap, once or twice every week, to remove any corroding substance that may exist around the teeth; care being taken to thoroughly rinse the mouth after its use.

225. _Food or drink should not be taken into the mouth when very hot or very cold._ Sudden changes of temperature will crack the enamel, and finally produce decayed teeth.

222. What is another use of the teeth? 223-232. _Give the hygiene of the teeth._ 223. How can the teeth be preserved? By what means? 224.

How often should they be cleansed? 225. What is said of very hot or cold drinks?

_Observation._ On this account, smoking is pernicious, because the teeth are subjected to an alternate inhalation of both cold and warm air.

226. _The temporary teeth should be removed as soon as they become loose._ If a permanent tooth makes it appearance before the first is removed, or has become loose, the milk tooth, although not loose, should be removed without delay. This is necessary that the second set of teeth may present a regular and beautiful appearance.

227. _In general, when the permanent teeth are irregular, one or more should be removed._ If the teeth are crowded and irregular, in consequence of the jaw being narrow and short, or when they press so hard upon each other as to injure the enamel, remove one or more to prevent their looking unsightly, and in a few months the remaining teeth, with a little care, will fill the s.p.a.ces.