98 R. F. SOGNNAES 



ganic matter in other resorbable tissues that one is almost forced to 

 disregard the basic role of inherent organic components within the 

 tissues being resorbed — as we have already disregarded the role of 

 interstitial cellular components — in the basic process of resorbability. 

 In conclusion, then, it is believed that the general significance of 

 dental resorption phenomena rests on the observation that resorb- 

 ability must be largely controlled by the consistent presence of a 

 highly vascularized adjacent tissue environment rather than by 

 some peculiarly consistent feature characterizing the structures that 

 are being resorbed, whether these be enamel, dentin, ivory, cemen- 

 tum, or bone, in various states of calcification or with various chemi- 

 cal and physical characteristics of the organic and inorganic constit- 

 uents (Sognnaes, 1955, 1960fl, 1960fo). 



Dental Caries 



The problem of dental caries, the most universal of all human 

 ills, is being examined in several other chapters of this volume, from 

 the point of view of microstructure (Darling, chapter 6), ultra- 

 structure (johansen, chapter 7), chemistry (Gray and Francis, chap- 

 ter 8), and bacteriology (Keves and Jordan, chapter 9). 



As a preamble, however, to the principal theme of the present 

 chapter — in vivo, in vitro, and postmortem erosions — it seems im- 

 portant to recognize several characteristic features of dental caries 

 which are in sharp contrast to other types of hard tissue destruction 

 in general and to other types of dental pathology, notably dental 

 erosion, in particular (Sognnaes, 1959, 1962). 



In the first place, dental caries is characterized by a deep sub- 

 surface demineralization ( up to 1000 microns deep ) prior to collapse 

 of the tooth structure (i.e. prior to extensive proteolysis and "cavity" 

 formation). Secondly, the pathway of this process is intimately re- 

 lated to certain preformed structural patterns within the dental 

 hard tissues themselves. These are, in the enamel (a) the incre- 

 mental lines of Retzius, (b) the interprismatic substance, and (c) 

 the intraprismatic cross striations of the individual enamel prisms 

 (these zones are probably related; Sognnaes, 1949); and in the den- 

 tin (a) the normal growth rings of von Ebner, (b) the Owen's 

 contour lines (probably representing less than adequate calcification 



