116 R. F. SOGNNAES 



that Bodecker ( 1945 ) has hitherto made the only direct observations 

 on the environment in juxtaposition to dental erosion. These findings 

 led him to conclude that the erosion environment was distinctly 

 on the acidic side, a condition not requiring the involvement of a 

 chelating mechanism operating at the alkaline pH range. More 

 precise tests are badly needed. 



The assumption has been made that some keratinolytic micro- 

 organism or agent must be present as a primary factor in the de- 

 struction of enamel. On this theoretical ground, Schatz et al. (1957), 

 again from indirect observation, have concluded that wool fibers 

 may be proteolyzed by organisms indigenous to the oral environ- 

 ment. In the first place, however, the very classification of the or- 

 ganic matter of enamel as a keratin has been seriously questioned 

 in newer studies which suggest that the enamel protein is not 

 typical of either keratin or collagen (Piez and Likins, 1960; Glim- 

 cher et ah, 1961). Furthermore, we have recently been able to 

 demonstrate that during mineralization of enamel, the fibrillar 

 protein becomes so completely petrified that it would appear to 

 be virtually inaccessible until the mineral component has been 

 removed (Frank and Sognnaes, 1960; Frank, Sognnaes, and Kern, 

 1960). Until far more definitive facts are presented, one feels 

 obliged to conclude, therefore, that some agents capable of removing 

 the mineral fraction of the enamel would seem to be intimately 

 and probably primarily involved in this type of hard tissue de- 

 struction, both in erosion and in caries (see also chapter 25 by Jen- 

 kins and Dawes ) . 



Whatever the agent mav be that is responsible for such a pri- 

 mary dissolution of the mineral phase of the teeth in the initiation 

 of erosion, it seems obvious that a combination of such dissolving 

 effects with mechanical friction would lead to greater destruction 

 than one factor alone. This can be readily demonstrated in vitro. 

 Indeed, W. D. Miller (1907) arranged teeth in an artificial tooth- 

 brushing machine and showed that the abrasive action of a combina- 

 tion of gritty paste and powder, following prior exposure of the 

 teeth to acid, would result in greater tooth destruction than either 

 one of these exposures alone. More recently Steel and Browne 

 ( 1953 ) noted the more interesting point that teeth which, prior to 



