44 
ALVEOLAR PERIOSTITIS. 
tumour, either a sarcoma or carcinoma, having loosened the tooth and 
allowed food to enter. 
The disease develops more rapidly when the tooth has been fissured, 
allowing food or fluid to enter the alveolus, and when compound fractures 
of the jaw extend to the alveolus. Less frequently the malady arises 
from the root canal. During wear of the tooth the canal is progressively 
closed with cement substance. But should wear outstrip this protective 
piocess, the root canal and pulp are laid bare on the grinding surface; 
food or decomposing buccal secretions enter, and occasion purulent inflam¬ 
mation of the pulp (pulpitis purulenta). This may extend downwards to 
the base of the alveolus, reach the alveolar periosteum, and finally pro¬ 
duce purulent periostitis. In the lower molar of a five-year-old horse 
Frick found the pulp cavity occupied throughout its length of 4 inches by 
a fragment of straw, which had set up alveolar periostitis, and eventually 
dental fistula. 
Kitt states that in the molars of old horses the central invaginated 
portion of enamel often becomes worn away, and the pulp chamber 
exposed. Food then enters and produces pulpitis, which extends to the 
alveolar periosteum. 
Complicated fractures, or even external injuries, of the jaw may 
occasionally cause alveolar periostitis. 
This is commonest in young horses, in which the roots of both the 
upper and lower molars are at points only covered by periosteum and 
skin. In such cases injuries may directly affect the root itself or the 
alveolar periosteum, but the inflammation usually remains localised. A 
predisposition to alveolar periostitis is observed in various forms of 
faulty mouth, especially in the shear mouth, and where the teeth are far 
separated. In consequence of their slighter make and lesser strength, 
the lower molars are oftener diseased than the upper. The third and 
fourth molars are most commonly affected, which Gunther ascribes to 
their central position in the fan-shaped arrangement (fig. 27), and to 
tlieii consequent exposure to powerful compression, both from in front 
and from behind. 
Alveolar periostitis of the incisors is very rare in horses and ruminants, 
is geneially of a secondary nature, and is due to injury of the interdental 
space or compound fracture of the alveolar process. 
Though single teeth are often affected, it is common for several to 
become diseased together, frequently corresponding teeth, like the two 
third lower molars. The cause of this symmetrical occurrence is not 
quite clear, though it may be due to abnormalities during development. 
Where several neighbouring alveoli are diseased, and especially where 
the teeth are very loose, a suspicion of some new growth is always 
justified. 
