Figure 3 



Fig. 3a. The section of the natural lesion of Fig. 1 as viewed with polarized 

 light using a full-wave plate, first order red, has the typical appearance de- 

 scribed and illustrated (Fig. 3b) by Gustafson (1957). All zones except the 

 last highly decalcified fifth zone of an advanced lesion are visible. ( X 200. ) 



Fig. 3b. A schematic representation of an incipient carious lesion mounted 

 in Canada balsam, as viewed with polarized light using a full-wave plate, first 

 order red, according to Gustafson, shows the five characteristic zones, (l^epro- 

 duced from Acta Odoutol. Scand., 15, Fig. X (1957), with the kind permission 

 of the author and editor. ) 



Fig. 3c. The natural lesion of Fig. 1 as viewed in darkfield illumination with 

 ordinary light. A lesion viewed this way appears lighter than the usual bluish 

 gray of normal enamel and sometimes will almost glow as the surface does in 

 this sample. However, the surface glow in this case was an edge reflection effect 

 unrelated to the presence of the lesion, (x 200.) 



Fig. 3d. A section of a lesion produced by a 96-hour exposure at 37 °C to 

 a medium consisting of 0.002 m (^aCL plus 6 per cent hydroxyethyl cellulose 

 adjusted to pH 4.5 with hvdrochloric acid, as viewed with polarized light using 

 a full-wave plate, first order red. The similarity to the natural lesion of Fig. 3a 

 and the diagram of Fig. 3b is apparent. (X 200.) 



Figs. 3e and 3f. The same sections as in Figs. 8 and 9 and Figs. 12 and 

 13, showing the effect of increasing exposure time on lesions produced at 4°G 

 with a medium of 0.05 m lactic acid and 0.03 m CaCL plus 6 per cent hv- 

 droxvethyl cellulose adjusted to pH 3.5 when viewed with polarized light, full- 

 wave plate, first order red. 



Fig. 3e. After a 30-hour exposure only zone 1 of dark blue or purple de- 

 scribed bv Gustafson was visible. The sound outer layer was just appearing. 



(X200.)' 



Fig. 3f. At 120 hours, zone 2 (gold band) had appeared. (X 200.) 



Fig. 3g. A section of a lesion produced by a 96-hour exposure at 37 °C to 

 a medium consisting of 0.01 m lactic acid and 0.03 m CaClo plus 6 per cent 

 h\'droxyethvl cellulose (with high buffer content) adjusted to pH 3.5. At this 

 high rate of decalcification a whitish zone was formed in place of the usual gold 

 appearance of zone 2. ( X 200. ) 



Fig. 3h. A section of a lesion produced by interrupted exposures at 37 °C to 

 a medium consisting of 0.05 M lactic acid and 0.03 m GaClo plus 6 per cent 

 hydroxyethyl cellulose adjusted to pH 4.0. The sample was removed every 48 

 hours, washed 5 minutes with distilled water, and returned to tlie decalcification 

 medium. The total exposure was 240 hours. Zone 2 (gold band) became very 

 broad by reason of the long cycling exposure. (X 200.) 



Fig. 3i. A section of enamel (same as in Fig. 37) after a 15-day exposure 

 at room temperature to a solution of hydrochloric acid at pH 4.5, viewed with 

 polarized light using a full-wave plate, first order red. A decalcification near 

 the svnface is visible and there are signs of zones similar to those seen in Figs. 

 3a and 3b. (X 200.) 



Fig. 3j. A section of enamel (same as in Fig. 38) after a 15-day exposure 

 at room temperature to an aqueous solution of 0.0005 m CaCL and 0.0005 M 

 NaHoP04 adjusted to pH 4.5, viewed with polarized light using a full-wave 

 plate, first order red. The appearance of the lesion bears no resemblance to 

 Figs. 3a and 3b. The uniformitv throughout the lesion is striking. (X 200.) 



218 



