96 R. r. SOGNNAES 



fects of radiation brought about b\' accidental ( radium dial paint- 

 ers) or therapeutic (cancer treatment) exposures. 



Dental Resorption 



The dental hard tissues are subject to bonelike resorption proc- 

 esses in the presence of osteoclast-like multinucleated giant cells 

 situated in characteristic Howship's lacunae along resorbing surfaces 

 of cementum, dentin, and, in some cases, even enamel. Of general 

 significance in this connection are, on the one hand, the environ- 

 mental and svstemic conditions under which these resorptive con- 

 ditions occur, and, on the other, the range of composition or nature 

 of the resorbing tissues themselves (Sognnaes, 1955, 1960/?). Typi- 

 cal examples of resorption within the dental apparatus are described 

 elsewhere (see Bhaskar, chapter 12, and Reichborn-Kjennerud, 

 chapter 11); we are here specifically asking ourselves what light if 

 any the dental aspects of this process may shed upon the funda- 

 mental explanation of resorbabilit\' per se. 



In the first place, it is noteworthv, in the case of dental resorp- 

 tion, that the origin of the multinucleated osteoclasts ( perhaps more 

 appropriately called "odontoclasts") cannot be attributed to the 

 fusion of antecedent uninucleated cells within the tissues undergo- 

 ing resorption. Neither enamel, dentin, nor primary cementum con- 

 tains interstitial cells. 



In physiological shedding of the teeth we have shown typical 

 lacunar giant cells in juxtaposition to the resorbing dental enamel 

 (Sognnaes, 1959, 1960i>), a tissue completelv devoid of even proto- 

 plasmatic extensions of any antecedent cellular elements. The den- 

 tin, which undergoes typical lacunar resorption both in normal 

 shedding and under pathological conditions of internal resorption 

 ("pink tooth"), has no connective tissue cells within its matrix, albeit 

 permeated by long cytoplasmic processes from the pulpal odonto- 

 blasts. In the case of cementum there are to be sure cells embedded 

 in the widest periapical zone of secondary cementum (cemento- 

 cytes ) , but the primary cementum is completelv acellular and yet in 

 no way spared from the same resorbabilitv in the presence of typi- 

 cal multinucleated giant cells which obviouslv must originate from 

 the adjacent environment (e.g. enamel resorption, see Fig. 30e). 



