DENTAL HARD TISSUE DESTRUCTION 107 



necessarily reveal gradients in demineralization near the surface. 

 Fortunateh', howe\er, through the recently refined method of 

 inicroradiograph\-, utilizing soft x-ra\s, between 5 and 30 kv, and 

 a yery fine-grained photographic emulsion (Kodak spectroscopic 

 plates, 649-GH), it is now possible to produce yery accurate x-rays 

 of thin sections of bones and teeth which can be enlarged photo- 

 graphically under the microscope up to 1000 times. The accuracy 

 of this method can be as good as 1 micron, making it possible to 

 detect differences in microdensity and potential demineralization 

 gradients near the surface of dental erosions. 



Our own microradiographic obseryations haye so far primarily 

 been made on the superficial areas in lesions extending into the 

 dentin, as exemplified in Fig. 5. In the bottom of these typical 

 wedge-shaped lesions, we haye been able to demonstrate that there 

 can occur a change in the surface of the tooth substance, charac- 

 terized by a gradient in the microdensity and indicating that de- 

 mineralization may occur to a maximal depth of 100 microns 

 (Fig. 6). This, it should be noted (as pointed out elsewhere: 

 Sognnaes, 1959), is less than one-tenth of the demineralization 

 gradient which can be observed in dental caries. In other words, 

 in erosion the alterations are strictly confined to a surface effect. 

 Occasionally the microstructure of the surface may exhibit a some- 

 what uneven configuration ( Figs. 7 to 9 ) , but even then there is no 

 evidence of the deep destruction along the dentinal tubules so 

 characteristic of caries. At other times, in certain parts of the lesion, 

 the surface mav be very smooth (Fig. 10), with little or no evidence 



Figs. 5 to 12. Microradiographs prepared by placing ground sections on 

 fine-grained spectroscopic plates (Kodak 649-GH), exposed to soft x-rays (25 

 kv). In Fig. 5 the deep wedge-shaped buccal erosion cavity appears to exhibit 

 no remarkable surface changes at low magnification (x 4). Figures 6 to 10 

 show at 100 times magnification that the erosion surface may exhibit a periph- 

 eral demineralization gradient. Figure 6, enlarged from bottom of wedge- 

 shaped defect in Fig. 5, shows that this demineralization can reach a maximal 

 depth of 100 microns. At certain stages the erosion lesions can be slightly 

 irregular (Figs. 7 to 9), and at others quite smooth and dense as though 

 there had been a redeposition of minerals in the periphery (Figs. 6 and 10). 

 By comparison, mechanical abrasion, whether produced in vivo (Fig. 11) 

 or in vitro (Fig. 12), shows verv smooth lesions with no subsurface loss in 

 microdensity. 



