VETE1UNART DENTAL SURFER}'. 77 



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 quan- 

 tity on the fang and at the expense of the perfectly 

 formed dentine lying in immediate contact with its 

 inner surface. That is to say, this layer of dentine is 

 converted into crusta-petrosa by the dental lacuna? 

 undergoing dilatation and becoming identical with the 

 hollow 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 oblitera- 

 tion of its pulp cavity, to serve all purposes as a part 

 of the living organism. This is the natural con- 

 dition of old teeth; but when the pulp cavity is ob- 

 literated 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 with the enamel 

 into the interior of the tooth, splitting up the tooth 

 into several perpendicular fragments from crown to 

 fang. 



