Hardness Tests on Sound Enamel and Artificially Demineralized White Spot Lesions

The accuracy and reproducability of hardness measurements have been investigated in this study. Sound and demineralized enamel were used as the main test materials. The reproducability of hardness measurements on artificial white spot lesions produced by a hydroxyethyl cellulose/lactic acid demineralizing solution was also investigated on embedded cross-sections. The operator error was found to be less than 5% when reading both steel and enamel indentations. The maximum hardness of the surface layer and the minimum hardness of the subsurface lesion were measured in three positions in each of 10 artificial white spot lesions. An analysis of the results showed that: (a) the hardness values at the same distance from the surface but in different areas of the same lesion were very similar; (b) hardness values between lesions were also very even; (c) the drop in hardness after demineralization was related to the initial hardness of the enamel.