508 DISEASES AND INJUEIES OF THE FACIAL EEGION". 



I need scarcely remind the professional reader that the integrity 

 of the teeth depends upon a due supply, both as to quantity and 

 quality, of nutritive materials. On the fangs of the recently cut 

 tooth but little crusta-petrosa is met with compared with that 

 which exists in old teeth. As ao^e advances the crusta in- 

 creases, and the tooth grows from the outside. 



In man, it is generally agreed that after a given time the den- 

 tine ceases to be produced, and the pulp becomes converted into 

 osteodentine. In the horse, the pulp cavity becomes obliterated 

 gradually by the pulp continuing to form dentine, the pulp simply 

 giving way to its own product, which ultimately occupies its 

 place and fills up its cavity. 



In proportion as the pulp diminishes, so is the supply of 

 nutriment to the tooth lessened, until at length it is entirely cut 

 off from the interior ; and to provide for the vitality of the tooth 

 under these circumstances the crusta-petrosa increases in quantity 

 on the fang, and at the expense of the perfectly formed dentine 

 lying in immediate contact with its inner surface. That is to 

 say, tliis layer of dentine is converted into crusta-petrosa by the 

 dentinal lacunae undergoing dilatation, and becoming identicaJ. 

 with the jioUow spaces or cells of the crusta. The tooth now 

 draws its nourishment from the blood-vessels of the socket, and 

 thus it continues long after the obliteration of its pulp cavity to 

 serve all purposes as a part of the living organism. This is the 

 natural condition of old teeth; but when the pulp cavity is 

 obliterated at an early age, by a too rapid formation of dentine, 

 and consequent obliteration of the pulp when the crusta is not 

 yet sufficiently developed to supply nourishment to the whole 

 tooth, caries must be the result. 



Many cases of caries of the teeth that have come under my 

 observation have resulted from the above cause, and very often 

 the disease is confined to that part of the crusta-petrosa that 

 dips Avith the enamel into the interior of the tooth, splitting 

 up the tooth into several perpendicular fragments, from crown 

 to fang. 



Caries of the neck (cervixj or the tooth is seen in those horses 

 whose teeth are wide apart, and is caused by the food remaining 

 in the interspaces, and by decomposition exciting inflammation 

 in the periodontal membrane. 



Caries of the neck is very commonly met with in dogs, some- 

 times causing abscesses in the cheeks. 



