DENTAL FISTULA. 
55 
almost always results from alveolar periostitis, the inflammatory process 
extending and producing an osteomyelitis purulenta, which finally leads 
to perforation externally. Inflammation then abates, until the alveolus 
alone remains inflamed. The small quantities of pus produced find exit 
through the communicating sinus. 
Dental fistula occurs oftenest in young horses. It affects the first and 
second pre-molars, seldom the third, and is commoner in the lower than 
in the upper jaw. Fistula is very rare in the molars, because their roots 
are covered by thick masses of muscle, and in the upper jaw project into 
the superior maxillary sinus. Despite these 
facts, such fistulse do occur. They open into 
the superior maxillary sinus or into the nostril, 
producing empyema of the sinus and chronic 
nasal discharge, which gives the peculiarly 
offensive smell of alveolar periostitis. 
In dogs, dental fistuhe originate most fre¬ 
quently from the upper molars. The outer 
opening is usually near the lower eyelid, and 
might be mistaken for that of a lachrymal 
fistula, were it not that probing shows it to 
communicate with a molar tooth. For a 
description of several cases of dental fistula 
in the horse, dog and cat, see p. 331 of Cadiot 
and Dollar’s “ Clinical Veterinary Medicine 
and Surgery.” 
Causes. Fistula, though generally preceded 
by alveolar periostitis, may be produced by 
complicated fractures or injuries of the 
maxilla. Hertwig believed pre-molar fistulas 
in the lower jaw to be commonly caused by 
wounds inflicted by narrow and inclined 
mangers. We can support this view, having- 
seen many cases of pre-molar fistula in young animals exhibiting no 
disease of the alveolus, but traceable to external injury of the posterior 
border of the lower jaw. The root of the tooth is often thickened, sui- 
rounded by actively-growing granulation tissue, which becomes covered 
with fresh cement; a periostitis alveolaris ossificans lesults, with 
formation of hyperostosis radicis (fig. 35), and extraction is lendeied 
difficult, or even impossible. 
The symptoms consist in the appearance of a little funnel-shaped 
depression in the skin, either of the lower margin of the under jaw, 
or of the upper jaw at the height of the roots of the pie-molais. Some¬ 
times the fistula opens within the mouth near the affected tooth. A fine 
Fig. 35.—Periostitis alveolaris 
ossificans of the third molar 
(horse). 
