The micro-hardness of enamel and dentin.

THE hardness of enamel and dentin has been determined by a variety of methods including abrasion," 2 pendulum,' scratch,4-7 and indentation" teehnics. Since the hardness of enamel and dentin has been shown to have considerable local variations, the methods using a microscratch or microindentation have been preferred. One of the more common types is the Knoop diamond indenter14 which has been used by a number of investigators.', 12, 15, 16 It should be mentioned, however, that in spite of the fact that the indentations are extremely small, they still represent a macroindentation when compared to the microstructure of enamel and dentin. The majority of the published hardness data for enamel and dentin has been measured on ground sections, although several papers'0 13 reported the hardness of intact enamel surfaces. The conclusions in regard to the difference in hardness from one section of a tooth to another are at times in variance with each other. This study of dentin and enamel was undertaken in an attempt to establish any trends in hardness existing from one area of a tooth to another or between different types of teeth. With this purpose in mind, this research did not attempt to relate the hardness values to the histologic tooth structure, but a sufficiently large number of hardness measurements were made so that the data could be treated on a statistical basis.