224 



J. A. GRAY AND M. D. FRANCIS 



Comparison of in Vitro and Natural Lesions 



The equivalence of natural incipient carious lesions to those pro- 

 duced by the in vitro system will be established, and, at the same 

 time, the effects of some of the variables will be qualitatively de- 

 scribed. The microscopic appearance, using ordinary transmitted 

 light (Fig. 4), of a lesion produced in 24 hours with a solution of 



5 



Figs. 4 and 5. A section through an incipient caries-hke lesion prodviced by 

 a 24-hour exposure at 4°C to a medium consisting of 0.05 m lactic acid plus 6 

 per cent hydroxyethyl cellulose adjusted to pH 3.5. 



Fig. 4. In ordinary transmitted light, the lesion can be seen to have pene- 

 trated about 30 microns. The right side of the surface, protected from the 

 medium by a varnish coating, provides a control for comparison. ( X 200. ) 



Fig. 5. A microradiograph shows that a considerable loss of material from 

 the subsurface lesion had occurred. There is slight evidence of a relatively 

 sound outer layer at the surface over the decalcified region of the lesion. The 

 surface of this sample, when viewed under a metallurgical microscope with 

 top illumination, was slightly dissolved by the medium. (X 200.) 



