108 R. F, SOGNNAES 



of a detectable demineralizatioii gradient. Indeed, the very periph- 

 ery of certain parts of the lesion can at certain stages show a 

 somewhat elevated microdensity (Fig. 6). It is qnite possible that 

 the lesion mav assume a transitionallv chronic stage in which there 

 may be some slight redeposition of minerals in the organic matrix 

 of the previously demineralized tooth substance. 



For comparative purposes, we have examined lesions believed to 

 represent uncomplicated abrasion in vivo (Fig. 11) as compared 

 with destruction produced in vitro by mechanical friction (Fig. 12), 

 For the latter purpose, extracted teeth were placed in a so-called 

 tooth-brushing machine (courtesy of the Miami Vallev Laboratories 

 of the Procter & Gamble Company, Cincinnati, Ohio), and exposed 

 to brushing with a tooth paste slurry for a period of time equivalent 

 to years of tooth brushing under practical conditions. The surfaces 

 of these lesions were similar in vivo and in vitro (Figs. 11 and 12), 

 exhibiting a smooth contour without anv evidence of subsurface 

 demineralization. Admittedly a surface which has become demin- 

 eralized, even though to a slight depth, could well be susceptible 

 to further loss by mechanical friction, if within the accessible range 

 of rigorous tooth brushing. In that case, this would be a secondary 

 factor, assuming that our observation of a superficial demineraliza- 

 tion gradient is indicative of some other chemical agent which, as 

 a primary factor, would tend to demineralize the tooth surface. 



Histopathologij 



Following the obsei^vation that dental erosion can exhibit a 

 surface demineralization, at least at certain stages, it seemed of 

 interest to explore more precisely, in stained decalcified sections, 

 whether or not the lesion mav be exhibiting anv other charac- 

 teristics which might explain this peculiar peripheral pattern. 



Paraffin sections were prepared following decalcification accord- 

 ing to the method of Morse ( 1945 ) . From a microscopic point of 

 view, the active lesions did not always look as "clean" as would 

 appear from gross appearance. Thus, we noted a thin zone of 

 organic material attached to portions of the eroded surface, as 

 illustrated in Figs. 13 to 18. In some instances (Figs. 13 to 15) the 

 tooth surface was very straight and smooth, even though over- 



