222 J. A. GRAY AND M. D. FRANCIS 



ions, such as fluoride (Brudevold, 1948). It lias been shown, how- 

 ever, that a reduction in solubihtx approaching ahnost complete 

 protection results from the naturally occurring organic coating on 

 enamel, the acquired enamel cuticle ( Meckel, 1961 ) , and this de- 

 posit has since been found to penetrate enamel to a depth of several 

 microns, which makes its removal difficult. In previous studies of 

 chemical svstems which produced caries-like lesions in enamel, the 

 original enamel surface was left essentially intact, retaining either 

 all or remnants of the insoluble organic coatings and the inorganic 

 ions which reduce enamel solubilitv. 



On the basis of the preceding argument, an organic material was 

 considered to be a necessarv component of anv decalcification me- 

 dium in addition to acid and acidic buffer. Furthermore, in order 

 to define the role of the organic material to be used in making in- 

 cipient carious lesions in vitro, the enamel should retain none of the 

 original surface and should consist entirelv of subsurface enamel. 

 For this purpose, all samples of enamel used in the present studies 

 were acid etched after mounting and ground with abrasive to re- 

 move the surface laver as ascertained by solubility rate measure- 

 ments (Gray, 1962). Enamel samples consisted of squares (ap- 

 proximately 4X4 mm- ) cemented to the ends of a plastic rod with 

 a dental plastic. All sides of the enamel were coated with the plastic 

 cement, leaving onlv the surface exposed. 



A suital:)le organic material was selected experimentalh'. An ex- 

 amination of past effective in vitro systems indicated that such a 

 material should be polymeric. Meckel (personal communication) in 

 studying the components of the agar-saliva system (Francis and 

 Meckel, 1968) found agar, saliva, proteins, and selected amino acids 

 to be effective to varying degrees. A variety of water-soluble poly- 

 mers was then tested using synthetic chemicals, natural products, 

 and derivatives of natural products in an attempt to find an effective, 

 well characterized material. The test consisted of mixing the polymer 

 with a solution of 0.05 m lactic acid, immersing a sample of enamel 

 in a few grams of the medium, and examining the sample visuallv 

 at intervals for defects resembling incipient carious lesions. Con- 

 trol areas were provided by coating a corner of the enamel with a 

 dental cavitv lining varnish. The qualitative results of such tests 



