DENTAL HARD TISSUE DESTRUCTION 109 



lain by a thin mucous plaque containing microorganisms. In such 

 cases we have noted a \'erv thin cuticular meml^rane separating 

 the microorganisms from the tooth surface proper. 



At higher magnification (Fig. 17) this thin membrane may best 

 be seen when stained with toluidine blue, with which it stains 

 green, that is orthochromatically, in contrast to the bacteria-laden 

 mucous film, which is intensely metachromatic with this dye. In 

 other instances (Fig. 16) a metachromatic mucous plaque laden 

 with bacteria appears to be in direct contact with the tooth surface 

 without being separated by the orthochromatic organic film. Under 

 this circumstance a superficial destruction of the tooth substance 

 may be visualized. At higher magnification (Fig. 18) it is note- 

 worthy that the surface destruction is primarily occurring in the 

 matrix proper between the dentinal tubules. This is in sharp contrast 

 to the bacterial invasion of the teeth in caries, in which the dentinal 

 tubules become invaded at an early stage and to considerable depth 

 prior to intertubular matrix destruction. Figure 18 illustrates this 

 characteristic feature of erosion. The dark material represents bac- 

 teria situated in a mucous film, and it will be noted that the inter- 

 tubular matrix is becoming destroyed without any widening of the 

 dentinal tubules. 



The possible bacterial implication in the etiology of dental ero- 

 sion, suggested by these findings, does not appear to have received 

 serious attention in the literature. This is perhaps not surprising in 

 view of the fact that dental erosion usually looks so extremely clean 

 to the naked eye. It must be remembered, however, that what is 

 seen in the microscopic sections represents an extremely thin film, 

 and since we have noted its relative absence in some areas of the 

 lesions as compared with others, this film may be transitory and not 

 always present. 



The basic issue raised by these observations is whether or not 

 the pathogenesis of erosion, albeit clearly different from that of 

 caries (Sognnaes, 1959), is of inherently dental or oral environ- 

 mental origin. Some peculiar characteristic of the tooth substance 

 itself could theoretically invite destruction of the intertubular ma- 

 trix along a surface area rather than invasion through the dentinal 

 tubules in depth. On the other hand, the superficial environmental 



