672 THE TEETH. 



ivory, consisting likewise in a chemical decomposition of its elements, may 

 sometimes, though rarely, remain passive ; but most frequently they deter- 

 mine in the tissue phenomena of reaction that manifest themselves by the 

 appearance of a cone or white zone, formed by a mass of canalicules obliter- 

 ated in consequence of a formation of secondary dentine. The tooth attacked 

 by caries does not remain passive and inert, but may in some measure under- 

 take to resist its action by the phenomena of condensing dentification of the 

 ivory. The agent of dental caries is the saliva, become the medium of acid 

 fermentation or the vehicle of foreign substances susceptible of altering 

 directly the tissues of the ivory and the enamel. The intimate mechanism of 

 the production of caries is a simple solution of the mineral and calcareous 

 salts which enter into the constitution of the enamel and of the ivory, by the 

 agent of new formation." 



Leber and Rottenstein* say : " The action of acids alone does not account 

 for all the phenomena which appear in caries of the teeth. The acids attack 

 first the enamel and rapidly change it to a chalky mass ; later on their action 

 is felt in a marked manner upon the dentine, which becomes more transparent, 

 and, in fine, as if cartilaginous, by the very slow, but progressive loss of its 

 calcareous salts. Caries, on the contrary, proceeds slowly in the enamel ; it 

 is much swifter in the dentine, where it proceeds promptly along the canali- 

 culi. This difference of progress must be attributed to the participation of 

 the fungi in the work of the caries. The elements of the fungus glide easily 

 into the interior of the canaliculi, which they dilate, and thus favor the passage 

 of the acids into the deeper parts ; these same elements cannot penetrate a 

 compact enamel, or at least they enter more slowly, and only when the ele- 

 ments which form it have been greatly changed by the action of acids. . . . 

 For them (the leptothrix) to be able to penetrate thus, it is necessary that the 

 teeth be in a suitable condition ; the enamel and the dentine must have lost 

 their density by the action of acids." 



Carl Wedlt says : " It was quite natural to transfer to the teeth the signi- 

 fication implied in the expression ' Caries of bone ; ' indeed, the fundamental 

 phenomena, namely, the destruction of the hard tissues, offered a striking 

 analogy. In their development, however, the two processes by no means pre- 

 sent such an identity. Caries of bone, as is well known, is an inflammatory 

 process (osteitis) which originates in the soft parts of the bone and erodes its 

 hard tissue. This is not the case with the carious process in the teeth, which 

 commences in the hard tissues and spreads to the vascularized and nervous den- 

 tal pulp. In sections made in a direction transverse to the axis of the radiating 

 dentinal canals, a greater or less number of canals are met with whose limit- 

 ing walls (the so-called dentinal sheaths) describe unusually large circles, and 

 whose cavities are replete with a mass which has in some places a homogeneous, 

 in others a molecular appearance, and forms convex projections beyond the sur- 

 face of the section. The transverse diameters of the widened and filled canals 

 vary, some being at least three times as large as others. The intertubular 

 tissue presents a molecular cloudiness, and is beset with grains having the 

 appearance of fat. . . . Since we know that an interchange of material takes 

 place in the dentine and cement during life, as is proved by the occurrence of 

 atrophies, hypertrophies, and new formations, and that the dentine possesses 

 a degree of sensibility, we cannot reject absolutely the idea of a reaction on 

 the part of both hard tissues against the effects of external agents. Some 



* " Dental Caries and its Causes," 1873. t " Pathology of the Teeth," 1872. 



