DENTAL HARD TISSUE DESTRUCTION 125 



particularly common in teeth which presented a dull, porous appear- 

 ance of the external root surface, a lower than normal weight, and 

 a greater penetration by x-rays. The presence of the canals in the 

 dentin explains the enhanced transmission of x-rays as well as the 

 scattering and, hence, hampered transmission of ordinary light 

 through ground sections, especially when viewed at low power. 



The cementum covering the root dentin of the teeth did not prove 

 a barrier to the agents responsible for the canals. Where primary 

 penetration of the cementum occurred near the enamel junction, the 

 destruction might clinically and roentgenologically be mistaken for 

 cementum caries. Histologically, on the other hand, there were dis- 

 tinctive differences between the postmortem penetration and the in- 

 tra vitam type of invasion characteristic of caries. Unlike caries, 

 which usually follows definite pathways in a consistent relationship 

 to the morphological pattern of the teeth, the postmortem canals 

 were very irregular, running across rather than along the direction 

 of the dentinal tubules. Another histological characteristic, hinting 

 at postmortem destruction, was the absence of vital response in the 

 neighborhood of the "cavities" produced in the teeth after death. No 

 evidence of either secondary or transparent dentin, botli of which 

 are familiar reactions to intra vitam lesions of the teeth, could be 

 observed in a logical proximity to destruction of the type just de- 

 scribed. 



The enamel, which during life is so extremely susceptible to de- 

 struction in the form of dental decay, was not found to be invaded 

 or destroyed by the postmortem canals described above. The enamel 

 protein is very sparse and differs from typical collagen. 



Diffuse disintegration. Occasionally, the teeth had lost their 

 normal microscopic appearance owing to a more diffuse change in 

 the dentin. Ground sections of such teeth had lost their normal 

 transparency and appeared as if decalcified in strong acid, and yet 

 the hardness of the tooth substance indicated the presence of a high 

 content of relatively homogeneous inorganic matter believed to be 

 caused by secondary petrification. 



Surface erosion. In addition to the above-mentioned changes 

 in the internal tooth substance, the surface of the teeth occasionally 



