DENTAL HARD TISSUE DESTRUCTION 97 



As a second aspect of general significance, there appears to be 

 no common link between the conditions under which these gener- 

 ally protected dental hard tissues succumb to resorption. In no 

 case — even in physiological shedding — can one definitely point to 

 a generalized systemic influence, such as is found in the case of deer 

 antler resorption, where a definitive sexual cycle is involved (see 

 chapter 13 by Goss). Unlike antlers, the teeth of man resorb one 

 after another, summer and winter, over a long period of time be- 

 tween the ages of 6 and 13. But from a local environmental point 

 of view, the shedding teeth share with the shedding antlers a 

 juxtaposition to a highly vascularized pad of granulation tissue 

 studded with giant cells which clearlv must originate from the ad- 

 jacent connective tissue environment. Even in pathological tooth 

 resorption — be it internal (pulpal) or external (periodontal), of 

 local origin or caused by metabolic bone disease (hyperparathy- 

 roidism), traumatic occlusion, or radiation injury — one topically 

 finds proliferation of highly vascularized granulation tissue loaded 

 with giant cells in immediate juxtaposition to the resorbing ce- 

 mentum, dentin, or enamel, as the case may be. 



Finally, there are certain important differences in the structural 

 and chemical nature of the three dental hard tissues, cementum, 

 dentin, and enamel, which may help to clarify the question as to 

 whether or not the basic phenomenon of resorbability is dependent 

 to any significant degree upon the quality of the structures being 

 resorbed. 



In general, it may be said that the prevailing concepts of hard 

 tissue biology hitherto have been largely evolved from studies of 

 bone tissue characterized by minute inorganic crystals and a col- 

 lagenous organic framework — whether the concepts deal with the 

 process of resorbability or of calcifiability (Sognnaes, 1960fl). But in 

 the dental apparatus we are faced with a less than satisfactory ex- 

 planation for the deposition and removal of the large inorganic 

 crystals contained within the inadequately identified organic matrix 

 of enamel, a product of ectodermal cells, recently classified as a 

 cross-;8-linkage protein (Glimcher et ah, 1961). At best this is a 

 sparsely distributed organic framework. Thus, irrespective of its 

 chemical nature, the quantity is so low as compared with the or- 



