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 spaces. _Observation._ When it is necessary to remove a tooth, apply to some skilful operator. It requires as much skill and knowledge to extract teeth _well_, as it does to amputate a limb; yet some persons, who possess strong arms, will obtain a pair of forceps, or a tooth-key, and hang out the sign of "surgeon-dentist," although ignorant of the principles that should guide them. 228. _It is not always necessary to have teeth extracted when they ache._ The nerve, or the investing membrane of the root, may be diseased, and the tooth still be sound. In such instances, the tooth should not be extracted, but the diseased condition may be remedied by proper medication. There are many sound teeth, that become painful, as already mentioned, which are unnecessarily removed. -=-=-=-=-=-=-=-=-=-=-=-=