If a permanent tooth break through at a wrong place, it should immediately be corrected by the dentist. When this is done early, it presents no difficulties, for the tooth will take its proper position if the necessary space be prepared for it. If, however, the tooth is allowed to remain in a faulty position until it has grown to its full size, splints may he necessary to correct the malposition. Such occurrences may be avoided by having the mouth regularly examined by a dentist.
The importance of having healthy teeth should not be underrated. The process of digestion begins with the act of chewing, by which the food is reduced to small particles, admitting of easy action by the gastric juice. In the mouth the food also becomes moistened by saliva, which transforms starches into sugar, thus aiding digestion. The more thoroughly the food is masticated, the longer does it remain in the mouth, and the more intimately does it become mixed with saliva. But, if one or more teeth be diseased and painful, the affected side of the jaw takes no part in mastication ; and, as a consequence, the food becomes insufficiently chewed, and is not mixed with an adequate amount of saliva. This makes it necessary for the intestine to perform the additional task which, under normal conditions, should have been done by the saliva ; and this overtaxing of the intestine inevitably results in digestive disturbances Carious teeth, or teeth with decayed roots, often cause disastrous dis turbances to digestion. Food remnants, collecting in the cavities, afford good breeding-places for all kinds of bacteria. Even a healthy mouth harbours numerous bacteria, and it stands to reason that a mouth which offers such a fertile soil for their propagation contains a still greater number. At every meal some of these micro-organisms, together with the decayed matter in which they are lodged, are swallowed with each morsel of food ; and the effects from the repeated ingestion of these poisonous elements can not be neutralised by the intestinal tract. It becomes irritated, and gives rise to a considerable degree of indigestion. Aside from this, decayed teeth impart a very disagreeable odour to the breath. To convince oneself of the nauseating, fcetid smell arising from the decay of tooth-pulp, it is only necessary to introduce a piece of cotton into the cavity (for instance, by twining it around a match), and then smell it. It, therefore, becomes a duty to one's
fellow-men to keep the mouth and teeth clean and healthy.
The teeth are instruments of speech, besides being primarily the instru ments of mastication. The loss of even a single tooth causes difficulty in pronunciation, and produces disagreeable sibilant sounds which make speech indistinct. Persons gradually become accustomed to small gaps, and learn to let the teeth of the lower jaw take the place of lost ones in the upper jaw, or vice versa. But, if the corresponding teeth in the other jaw be also missing, speaking becomes a matter of more difficulty. Attention should, therefore, be paid to the care and preservation of children's milk teeth ; otherwise they may not learn to speak correctly, and their mental development may be retarded.
Another disagreeable result of missing teeth, or of large cavities in the incisors, is the constant outflow of saliva, which cannot be retained. Even when the mouth and teeth are healthy, the disease-germs which are always present in the mouth are thrown off with every drop of saliva. In the presence of decayed teeth or of inflammatory affections of the mucous membrane of the mouth, a still larger number of such disease-producing bacteria are ejected with the saliva. \\len the saliva evaporates on foot paths or in other public places, the micro-organisms are set free, constituting a menace to the health of other people. For this reason one should always spit in cuspidors containing some water or, better yet, some antiseptic solution ; and, above all, one should abstain from spitting in public conveyances or on the floors of public buildings.
The effect on the facial appearance caused by decayed, missing, of irregularly formed teeth, is sometimes very marring. An otherwise pleasant face may appear positively ugly when decayed or yellow teeth are displayed every time the person opens his mouth, or when the rows of teeth are broken by black gaps. On the other hand, a set of healthy, white teeth lends a charm to even a less attractive face. If an entire set of teeth is missing, the face becomes deformed. The cheeks and lips become sunken, and the face takes on the appearance of old age.