MICROHARDNESS STUDIES OF INTACT SURFACE ENAMEL

¹ Department of Biochemistry, Medical College and School of Dentistry, University of Alabama, Birmingham, Ala.

With the Knoop indenter, hardness measurements can be made on the intact enamel surfaces of extracted teeth in the outer 0.005 mm. The deviations of hardness values on the intact tooth surface usually are somewhat greater than for polished surfaces. A portion of the deviation seems to arise from the curvature of the surfaces.

The average hardness of the teeth studied was about 380 Knoop Numbers, similar to that for a hard stainless steel (370 K.N). Extreme variations fell in the range 250 to 500 K.N. Variation, almost to these extremes, could be found on some single surfaces, and appeared to represent local variations, with no consistent pattern.

Variations among tooth types in the same and different mouths, between surfaces on the same tooth, between deciduous, erupted, and unerupted teeth, and between teeth from individuals of different ages were not pronounced. The observed variation seemed generally to fall in the range that could occur on a single surface.