124 R. F. SOGNNAES 



Microscopic Examination 



The procedure used for microscopic sectioning of the teeth was 

 a petrification technique which utihzed a plastic material, methyl 

 methacrylate, for infiltration, hardening, and protection of the brittle 

 specimens during sectioning and grinding ( Sognnaes, 1947 ) . In ad- 

 dition, a few smaller slabs from selected specimens were prepared 

 as decalcified parafiin sections. 



Histologically, it was possible to distinguish between several types 

 of postmortem changes in the teeth. The enamel exhibited surpris- 

 ingly few histologic differences in appearance from that of freshly 

 extracted teeth. Cementum, dentin, and adherent alveolar bone, on 

 the other hand, showed striking histologic alterations that could 

 hardly have been predicted from gross inspection of the outer surface 

 of the specimens. 



Boring canals. It was found that abnormal canals, unlike any- 

 thing observed in freshly extracted specimens, either entered the 

 teeth from the inside through the predentin or penetrated the 

 cementum-covered roots from the outside. More than one morpho- 

 logical pattern of these canals could be recognized. One type was 

 characterized by long and naiTow canals which often penetrated 

 the whole width of the dentin in irregular fashion (Fig. 21). These 

 canals were 2 to 10 microns wide, occasionally wider, sometimes 

 exhibiting a corkscrewlike penetration, sometimes with several 

 branches, 15 to 25 microns thick. This seemed to be the commonest 

 type. The largest canals, and hence the most destructive ones, some- 

 times reached a diameter of from 50 to 100 microns and were easily 

 identified by the ampulla-shaped widenings shown in Fig. 22. 



Two of the most significant characteristics of these canals were, 

 first, their great width, which exceeded that of the normally present 

 dentinal tubules, and, second, the fact that the canals penetrated in 

 all directions and across the intertubular matrix rather than along 

 the dentinal tubules. Where the pulp cavity of the teeth was readily 

 accessible through a wide apical foramen, the canals were most fre- 

 quently found to enter the less calcified predentin zone and from 

 there to proceed toward the periphery. This type of change was 



