104 



R. F. SOGNNAES 



flattened (C, D, E), irregular (F), figured (G), circumscribed, and 

 wedge-shaped (H, I). 



Though tooth brushing had been considered an etiological factor 

 in erosion prior to the studies of Miller, it is noteworthy that several 

 years before the turn of the century, Kirk (1887) emphasized that 

 erosion could be found even in people who only brushed occasion- 

 ally, sporadically, or not at all. Further, he noted, as we have amply 

 illustrated above (Fig. 1), that there could be a great variation in 

 the intraoral orientation of the lesions on difi^erent teeth. He found, 

 furthermore, that people who brushed horizontally could neverthe- 

 less have lesions of erosion in the form of vertical grooves, that 

 eroded teeth could be separated by non-eroded ones, and that ero- 

 sion could occur, as we have noted, in teeth which were not acces- 

 sible to the toothbrush at all. 



Though it is true that typical dental erosion may ultimately as- 

 sume a very wedge-shaped appearance with sharp angles, this is 

 actually an advanced stage of pathology. In an earlier stage, we 



Fig. 3. Segment of labial surface of incisor with beginning erosion of 

 enamel (upper part) passing through dentin-enamel junction at one point and, 

 near cementum-enamel junction (below), producing deep wedge into the 

 dentin. (X 12.) 



Fig. 4. View of outer enamel surface removed from top of segment seen 

 in Fig. 3. To the left of the erosion grooves, prior to gross loss, is seen a slight 

 chalklike change in the opacity of the enamel. ( X 12.) 



