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

Abstract

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.

Abrasion Induced Volume Loss in Porcine Teeth Measured Using X-Ray Microtomography

“…Dentin has ∼60% hydroxyapatite, where cementum has between 45 and 50% (Ho et al, 2004;Srivicharnkul et al, 2005;Goldberg, 2011;FIGURE 4 | Plot of the average normalized changes in volume for the enamel and cementum/dentin vs. the cumulative brushing time (in minutes). Yamaguchi et al, 2016) The high mineral content of the enamel, over 90% (Habelitz et al, 2001;Goldberg et al, 2014;Yilmaz and Schneider, 2016), results in significant contrast to the cementum and dentin. Therefore, it is not possible to indicate when the abrasive behavior of the tooth brushing has completely removed the cementum and then begun to remove the underlying dentin.…”

The Role of RANKL and Involvement of Cementum in Orthodontic Root Resorption

“…Considering the abovementioned results, individual variations in the hardness and Ca/P ratio of cementum may influence the resistance or susceptibility to root resorption and could be involved in root resorption caused by orthodontic forces. Yamaguchi et al [5] demonstrated a positive correlation between the respective hardness of enamel and cemen-tum in humans (hardness: r = 0.551, p < 0.01, and elastic modulus, r = 0.552, p < 0.01). If cementum hardness can be estimated based on the value of enamel, it may be possible to accurately evaluate the risk of root resorption in each patient during orthodontic treatment.…”

“…The hardness (soft, moderate, and hard) and tissue mineral density (TMD) of the cementum in the apical region of the root have been measured using the dynamic micro-indentation method and X-ray µCT analysis, respectively. The cementum hardness values were lower in the soft and moderate groups than in a hard group [5], and the X-ray µCT analysis revealed that the teeth in the hard group had higher TMD values than those in the other two groups [6]. Therefore, the hardness of the cementum may be related to the occurrence of ORR.…”

“…Recent studies in humans have reported the presence of individual differences in the hardness of cementum near the apex and particularly the calcium (Ca)/phosphorus (P) ratio. A correlation was observed between the Vickers hardness and Ca/P ratio of the cementum in the apical region [5][6][7]. These findings suggest that the cementum hardness and the Ca/P ratio may be involved in the occurrence of ORR.…”

Heavily Induced Root Resorption Stimulates Wnt5a Expression in Cementoblasts

“…Patient-specific factors causing root resorption include allergies(1), chronic asthma (2), abnormal root (3), and the hardness and form of cementitious materials (4).…”