For the marginal ulcerations thus produced there is no better treatment, after removing tartar, than the local application of zinc iodide, either in fine crystalline form or in saturated solution. It is not so much the visible surfaces which need such application as does the gingival tissue in concealed locations and between the teeth. Zinc iodide is not only an excellent antiseptic, but a powerful astringent, and meets a double indication. It may be applied once a week or oftener.
The dental enamel is the protective medium which, being once injured, exposes the dentine beneath to the possibility of infection. Such injuries are mechanical, but usually minute. The practice of putting hot food into the mouth and immediately following it with a drink of iced water is calculated to crack the enamel on a tooth as it would on any other material. Such a crack, although microscopic in dimensions, permits the entrance of bacteria into the dentine, in whose tubules they multiply and produce minute amounts of lactic acid. The enamel will resist this acid almost indefinitely, but the softer dentine is dissolved by it, and in this way cavities are formed within the teeth, and the condition known as dental caries is engendered. While it requires the special art and training of the dentist to cope with such conditions, every general practitioner should be familiar with the circumstances under which these lesions are produced. Congenital defects of the enamel afford also the same opportunities for infection.
When infection has extended to the delicate pulp cavity and when one of the terminal fibers becomes exposed the condition is accompanied by more or less distress, and when the alveolar socket becomes involved the tooth is loosened, either temporarily or permanently, according as the condition is treated. Thus a small alveolar abscess, referred to as “gum-boil,” may result. In the former case there is usually a small sinus which leads down to the root of the tooth, either through the spongy bone or alongside the tooth itself.
Plate III illustrates the conditions in teeth undergoing various forms of caries, there being numerous bacterial forms responsible for different types of the disease.
Treatment here does not differ in principle from that for treatment of caries in bone. Its essential feature is actual removal of all infected dental tissue, with a combination of protection against further infection, and that substitution for lost tissue which is effected by the use of gold, amalgam, or some of the other fillings in common use among dentists. American ingenuity has reached its acme in the discovery of means and methods for atonement of tissue thus lost by disease, and American dentists certainly lead the world in the mechanics of their art. They go much beyond the mere filling of diseased teeth, but have devised substitutes for teeth actually lost, and much of the plate work of the past is now substituted by what is known as crown and bridge work.
Dentistry as a part of oral surgery has now become a specialty by itself. A competent dentist, therefore, is a necessary coöperator in the treatment of all diseases of the teeth.
It is mainly when disease has spread from the teeth to the surrounding bone and tissues that the surgeon as such intervenes. Caries and necrosis of a small or large part of either jaw may be the result of extension of disease processes having their beginnings as above. In the chapter on the Neck, when dealing with the subject of tuberculosis of the lymphatics, it is stated that a large proportion of such cases due to the propagation of infection from the oral cavity and often from the teeth.
There are two substances used in medicine and in the arts which have a proclivity for the tissues of the mouth and jaws. These are phosphorus and mercury, the former usually affecting the bone and the latter the softer tissues. Before legislation had been enacted by which the young were prevented from working in match factories phosphorus necrosis of the lower jaw was not uncommon. Today it is rarely seen. Again, in the older days when mercury was given in large amounts, and its effects were not as well guarded against as now, mercurial stomatitis proceeding to ulceration and even loss of teeth was not an uncommon event. Now it is seen only in those who have an idiosyncrasy which makes them peculiarly liable to its effects. The mechanism of phosphorus necrosis is supposed to be an ossifying periostitis, with formation of small osteophytes in the alveolar periosteum, which lower tissue resistance and permit easier invasion of bacteria from the mouth. (See [p. 428].)
The extension of disease from the teeth, especially of the upper jaw, upward into the antrum of Highmore, with its consequent infection, is elsewhere discussed, and the reader will find the treatment of empyema of the antrum considered in Chapter XXXVII.
The teeth are also subjects of certain tumor formations which in general are spoken of as odontomas, and have been mentioned in the chapter on Tumors. (See [p. 281].)