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?