DISEASES OP THE ALVEOLI. 289 



(D) DISEASES OF THE ALVEOLI. 



ALVEOLAR PERIOSTITIS. 



Alveolar periostitis (Periostitis alveolaris) is by far the commonest 

 dental disease of herbivora and carnivora, and especially of dogs. As 

 its development, symptoms, and causes vary considerably in different 

 classes of animals, it will be considered separately in each class. 



Alveolar Periostitis in Herbivora. The roots of the teeth are fixed 

 in the alveoli by the alveolar periosteum or alveolar dental mem- 

 brane. The outer layer of the periosteum lines the alveolus, the 

 inner layer the root of the tooth. At the point where the periosteum 

 becomes continuous with the outer surface of the jaw-bone the gum 

 is attached, and it serves to prevent foreign bodies or food entering 

 the alveolus. 



Depending on their character, two forms of alveolar periostitis 

 may be distinguished. (1) Chronic ossifying, and (2) purulent alveolar 

 periostitis. Those forms of alveolar disease resulting from local inva- 

 sions of actinomyces or from tumour formation are described else- 

 where. The chronic ossifying form is characterised by the formation 

 of exostoses at the root of the tooth, which appears either 

 roughened, or covered with flat, or knob-like masses of new 

 bone ; the latter greatly hindering the extraction of the tooth. In 

 the purulent form the periosteum is usually thickened and extremely 

 vascular ; at points it is covered with granulations, and separated 

 from the wall of the alveolus or root of the tooth by a quantity of 

 grey-coloured offensive bone pus. Opposite these points the bone 

 or root of the tooth is often eroded to the extent of one-sixteenth 

 of an inch or more. In occasional cases, one sees extensive bone 

 necrosis followed by suppurative osteomyelitis of the lower jaw. The 

 periosteum usually becomes diseased in spots or on one side of the 

 tooth, but in very old-standing cases disease may be so extensive 

 that the tooth lies loosely in the alveolus and can be removed with 

 the fingers. Frick has seen some cases where only a few plate-like 

 fragments, the remains of the enamel, filled the alveolus. In all 

 old-standing cases the smell is very offensive. 



The above two conditions are often associated, so that at one 

 point the tooth shows discrete exostoses and at another limited areas 

 of purulent alveolar periostitis. 



Causes. Alveolar periostitis almost always results from injury 

 to the gum, or its separation from the tooth. Fissures of the tooth 

 reaching to the root, and laying open the root-canal, occasionally 

 produce it. Portions of hard food, especially hard chaff, may easily 



