RELATION OF STRUCTURE TO THE MICROHARDNESS OF HUMAN DENTIN

THE HARDNESS of human dentin has been reported by a number of in-vestigators using a variety of methods. Wright and Fenske ' used an abrasion method which gave macroscopic results and reported that there was no relationship between hardness and anatomic position in dentin. They also reported that dentin in the teeth of females was significantly harder than in males and that the hardness of dentin in both approached a maximum at an age of 31 to 40 years. Hodge and MeKay2 used a microscratch method and stated that crown dentin was somewhat harder than root dentin, although the difference observed seems to be within the limits of experimental error. Zieger3 reported that the dentin increased in hardness with age, and Richter4 observed that dentin under areas of attrition or caries was harder than normal dentin. Likewise transparent dentin was reported by Proell and Schubert5 to be harder than normal dentin. Previous microhardness measurements from this laboratory6 on crown dentin established an average Knoop hardness number (KHN) of 68. It wa