DENTAL HARD TISSUE DESTRUCTION 131 



preliminary in nature) seem pertinent with regard to (1) in vitro 

 and in vivo tests of the gross and microradiographic appearance of 

 hard tissues exposed to deminerahzing agents, and (2) in vivo 

 capacity for remineraHzation of such partially demineralized lesions, 

 followed by (3) a few comments on the theoretical and practical 

 significance of such observations. 



7/1 Vitro Demineralization 



In following up earlier studies on various demineralization gra- 

 dients found in pathological destruction of enamel, dentin, and bone 

 (Sognnaes, 1959), it appeared of interest to determine to what ex- 

 tent these gradients were due to structural characteristics of the 

 tissues themselves. 



With this in mind various hard tissues such as enamel, dentin, 

 ivory, bone, and shells have been exposed to comparable chemical 

 agents capable of withdrawing minerals. Furthermore, these agents 

 have been placed in juxtaposition to the hard tissues with or with- 

 out prior removal of the natural surface lavers and with or without 

 admixture of other agents that mav influence the surface chemistry, 

 such as organic polymers ( hydroxyethyl cellulose) simulating sali- 

 vary mucin. At this point, only a few observations will be cited, 

 based on gross appearance and high-resolution microradiography 

 (Fig.25AtoE). 



When different mammalian hard tissues are exposed to identical 

 environments capable of withdrawing minerals, only the enamel ex- 

 hibits to any appreciable degree the characteristic opacity that is 

 so familiar in the naked-eve appearance of incipient caries. The 

 dentin and other mesenchvmal hard tissues, even if exposed within 

 the same over-all specimen to the identical agents, fail to exhibit 

 these optical surface changes. This difference in appearance between 

 enamel and dentin (Fig. 25C) in no way provides a true clue to 

 what is going on within the tissue. In both cases there is indeed 

 subsurface demineralization (Fig. 25D and E). Similarly one may 

 conclude that the clean and intact-looking dentin surface in the 

 bottom of a dental erosion lesion may not provide a true clue as to 

 subsurface changes. 



