DENTAL HARD TISSUE DESTRUCTION 111 



agent or agents, be tbe\' of bacterial, saliv^ary, or other origin, could 

 be such that their action would primarily attack the mineral phase 

 in the intertubular calcified matrix rather than have the capacity 

 to destroy and invade the tooth b}' way of its natural structural 

 pathways. For the moment, this important question can be discussed 

 only on the basis of very limited observations to be alluded to 

 below. 



Tooth Structure 



The structural quality of the teeth themselves has received limited 

 attention as a factor in susceptibilitv to dental erosion. Hopewell- 

 Smith (1918) related a case of erosion which he believed was ac- 

 centuated by faulty tooth structure, because sectioning of the 

 eroded teeth also showed uncalcified interglobular dentin spaces. 

 The latter defects, however, which have also been related to caries 

 susceptibility, are exceedinglv common as compared with erosion. 

 Indeed, surveys on the microstructure of human teeth from various 

 countries and periods of time indicate that such calcification defects 

 are almost universally present in the teeth of man (Sognnaes, 1956). 



Figs. 13 to 18. Toluidine blue-stained sections through dental erosion 

 lesions in the same mandibular incisor teeth seen grossly in Fig. 1 I at an inter- 

 mediate stage, and in Fig. 2 (insert) at time of extraction for microscopic 

 study. Figures 13 and 14 are plastic-embedded ground sections (X 100). The 

 eroded tooth substance appears relatively smooth and clean near the outer 

 enamel edge of the wedge-shaped erosion lesion (Fig. 13), which Involves 

 both enamel (E) and dentin (D). There is, however, a good deal of micro- 

 scopic surface irregularity and organic debris in the bottom part of the erosion 

 "cavity" (Fig. 14). Decalcified sections, Figs. 15 to 18, show variable amounts 

 of dark-stained surface deposits. Figure 15 (X 100) shows a relatively smooth 

 "cavity" surface and minimal debris even though the erosion has extended 

 through the primary dentin (PD) into the secondary dentin (SD) . Figure 16 

 (X 100) shows a microscopically more irregular erosion surface with varying 

 amounts of organic debris. Figure 17 at higher magnification (X 700) shows 

 a mucous metachromatic deposit (MD) about 15 to 20 microns thick sepa- 

 rated from the smooth tooth surface by a delicate orthochromatic membrane 

 (OM).l to 2 microns thick. This membrane may be protective since there is 

 no significant active destruction of the underlying tooth substance. In Fig. 

 18 a zone of active tooth destruction has been enlarged (X 500). A bacterial 

 plaque (BP) is here in direct contact with the tooth substance without any 

 separating membrane. The intertubular dentin matrix is being destroyed, but 

 unlike caries, there is no invasion of the dentinal tubules. 



