Decayed teeth are comparatively infrequent. The causes are said to be external injury, and chronic inflammation of contiguous structures, as gums inflamed by lodgment of food in the interdental spaces. It has been observed that caries is more frequent in horses having the teeth abnormally wide apart. Decay may commence at the fang, the neck, or the crown; the neck is perhaps the commonest seat of the disease. Among the symptoms of this disease are difficult mastication, quidding the food, slobbering at the mouth, enlargement of the jaw, which may be seen and felt from the outside, and in the case of upper molars a discharge of a fetid nature sometimes takes place through the nostrils. The fourth molar is said to suffer more frequently from caries than any other.

Caries.

Fig. 126. - Caries.

If disease begins at the fang, the life of the tooth is generally short, as nutrition is entirely cut off after a little while. Such a tooth has a dead look, is not quite so high as its fellows, and may be found to be loose. With diseased fangs abscesses are to be feared, and their presence is frequently the first intimation of anything wrong with the teeth. Unless suitable treatment is adopted, disease and disorganization may result and prove very intractable.

But little horse - dentistry has been practised beyond rasping and extraction, and there is little doubt that a good deal of discomfort might be saved, and operations avoided, by suitable stoppings being employed. Decay occurs rarely on the grinding surface, but at the sides; and the few experiments made have been so successful as to warrant us in clearing out a cavity and filling it up with a hard amalgam. This serves to keep out particles of food and prevent fetor of the breath; and provided the cavity is made dry at the time the stopping is introduced, further decay may be for a long time arrested. Gutta percha is a cheap and convenient stopping, and is worth a trial in mouths where the interdental spaces between the teeth are large and allow food to accumulate and prove a chronic source of trouble. It may also be used to fill a gap left where a tooth has been extracted.