^90 ALVEOLAR PERIOSTITIS. 



become insinuated between the tooth and the gum and remain fast, 

 movements of the tongue and cheeks not sufficing to remove them. 

 Purulent periostitis, with separation of the periosteum from the 

 tooth, supervenes. Masses of food penetrate into this enlarged 

 space, widening the division between the alveolar wall and the tooth, 

 and increasing inflammatory action. Separated from the periosteum, 

 the tooth loses its firm seat in the alveolus, and, yielding to the 

 resistance of its neighbour, is diverted from the common line, and 

 may be so displaced that it can be removed with the fingers. Its 

 root appears completely denuded of periosteum and bathed in pus. 

 Similar results are produced by the entrance of food between the 

 teeth, as happens in old age when the crowns are not in close contact. 



In dogs and horses, alveolar periostitis may result from epulis, 

 the 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 process, the root canal and pulp are 

 laid bare on the grinding surface ; food or decomposing buccal 

 secretions enter, and occasion purulent inflammation of the pulp 

 (pulpitis purulenta). This may extend downwards to the base of 

 the alveolus, reach the alveolar periosteum, and finally produce 

 purulent periostitis. In a 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 alveoli 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 teeth, especially in 

 shear mouth, and where the teeth are far separated. In consequence 

 of their slighter make and less strength, the lower molars are oftener 



