Individual Variations in the Hardness and Elastic Modulus of the Human Cementum

The purpose of this study was to measure the physical properties of enamel and cementum of permanent teeth and to determine the correlation between them. This study was conducted on 50 maxillary premolars that were collected from 26 orthodontic patients (10 males and 21 females, mean age: 19.51 years, range: 12-35 years). The hardness and elastic modulus of the enamel and cementum were measured at the surface of the crown and root at three locations (cervical third: CC, middle third: CM, and apical third: CA). There were individual differences in the hardness and elastic modulus of enamel and cementum. The hardness of the cementum decreased from the cervical to apical regions on the root surfaces in the moderate and soft groups (p<0.01). Individual variations were observed in the hardness and elastic modulus of the human first premolar cementum. A correlation was noted between the hardness and elastic modulus of the enamel and cementum in the CA group (hardness: r=0.551, p<0.01, elastic modulus: r=0.552, P<0.01). These results suggested that the physical properties of cementum may be involved in the occurrence of root resorption caused by orthodontic forces.