Inflammation frequently follows on caries, and the pulp is usually involved. It is almost certainly attacked if the caries causes penetration into the pulp, but before this takes place there is frequently some inflammation which expresses itself in a new-formation of Secondary dentine inside the tooth around the point to which the caries is advancing (see Fig. 386). In this way the carious cavity may be shut off from the cavity of the pulp, and so a more serious inflammation warded off. Very frequently, however, a more acute inflammation of the pulp occurs, with redness, swelling, great pain, not infrequently also with complete necrosis of the pulp, and, in consequence, of the whole tooth.

The inflammation often extends to structures around the tooth. The root-membrane or dental periosteum, which covers the root portion of the tooth, is the structure most directly attacked. This membrane is, as we have seen, intimately connected, towards the neck of the tooth, with the submucous tissue of the gums and the periosteum of the alveolar process of the jaw. Inflammations of these structures, especially of the gums, very frequently ensue, resulting in the well-known Gum-Boil, which often goes on to suppuration and abscess, forming the so-called Parulis. The abscess usually bursts into the mouth, but it may produce extensive swelling of the gum, and lead even to penetration outwards, resulting in a fistulous opening in the skin.

The result may be even more serious if the periosteum of the jaw becomes inflamed, resulting, it may be, in suppuration which is apt to be chronic. With the periostitis there is usually new-formation of bone, causing thickening of the jaw.

Inflammations of the root-membrane and periosteum of the jaw sometimes occur apart from caries, as a result, for instance, of poisoning with phosphorus or mercury, and in scurvy. In that case the inflammation is not limited to the. neighbourhood of one tooth, but extends probably to a series.