DENTAL HARD TISSUE DESTRUCTION 147 



Dental Caries 



The pattern of the initial carious lesion is intimately related to 

 certain structural pathways within the dental hard tissues that are 

 exposed to the external environment of the mouth. The destructive 

 process is pathologicallv specific. One of the most distinctive micro- 

 structural features of dental caries is a deep subsurface demineraliza- 

 tion of about 1000 microns, whether it be enamel (Fig. 30A) or 

 dentin (Fig. SOB), prior to invasion of the tissues by oral micro- 

 organisms (Fig. 30a) and proteolvtic disintegration of the organic 

 matrix (Fig. 30b). In this respect, dental caries is markedly different 

 from other tvpes of hard tissue destruction (see Fig. 31), in which 

 subsurface demineralization and preformed structural pathwavs do 

 not appear to be b\' far so significantlv involved in the pathogenesis 

 of the lesions. The relativelv higher resistance to demineralization 

 observed within a narrow surface zone of incipient enamel caries 

 ( Fig. 30A ) ma\^ be explained in part by the higher fluoride content 

 now known to be present in this zone and in part by what has been 

 suggested to be a protective interaction of organic surface films de- 

 posited on the inorganic phase of the tooth substance from the adja- 

 cent liquid phase of saliva. 



Dental Erosion 



The gross distribution and morphological variety of idiopathic 

 dental erosion defects preclude a simple mechanism of mechanical 

 wear as a primary cause of this disease. 



Microradiographic observations of ground sections have shown at 

 certain stages a minute subsurface demineralization gradient (Fig. 

 30C) never seen to exceed 100 microns in depth (i.e., less than one- 

 tenth of what can be found in incipient caries ) . Consequently, one 

 cannot, in beginning erosion, detect any change in opacity by naked- 

 e\e inspection so as to distinguish the lesion from simple abrasion, 

 in which there is no subsurface demineralization at all (Fig. 30D). 



Histological examination of stained decalcified sections suggests 

 that dental erosion is not necessarily de\'oid of surface deposits of 

 bacteria-laden mucus (Fig. 30C), though the lesion may look clean 

 to the naked e\'e. Occasionalb, these superficial deposits may be 



