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. 2014 Feb 6:5:1758736014520809.
doi: 10.1177/1758736014520809. eCollection 2014.

Comparison of mechanical property and role between enamel and dentin in the human teeth

Kj Chun  1 , Hh Choi  1 , Jy Lee  2
Affiliations

Comparison of mechanical property and role between enamel and dentin in the human teeth

Kj Chun et al. J Dent Biomech. .

Abstract

The mechanical properties of enamel and dentin were studied using test specimens having the same shape and dimensions because these properties might vary with the experimental conditions and specimen shapes and dimensions. Healthy human teeth were used as specimens for mechanical tests. The stress (MPa), strain (%), and elastic modulus (E, MPa) of the specimens were obtained from compression tests. The maximum stresses of the enamel, dentin, and enamel-dentin specimens were 62.2 ± 23.8, 193.7 ± 30.6, and 126.1 ± 54.6 MPa, respectively. The maximum strains of the enamel, dentin, and enamel-dentin specimens were 4.5 ± 0.8%, 11.9 ± 0.1%, and 8.7 ± 2.7%, respectively. The elastic moduli of the enamel, dentin, and enamel-dentin specimens were 1338.2 ± 307.9, 1653.7 ± 277.9, and 1628.6 ± 482.7 MPa, respectively. The measured hardness value of enamel specimens (HV = 274.8 ± 18.1) was around 4.2 times higher than that of dentin specimens (HV = 65.6 ± 3.9). Judging from the measured values of the stress and strain of enamel specimens, enamel tended to fracture earlier than dentin; therefore, it was considered more brittle than dentin. However, judging from the measured hardness values, enamel was considered harder than dentin. Therefore, enamel has higher wear resistance, making it suitable for grinding and crushing foods, and dentin has higher force resistance, making it suitable for absorbing bite forces. The different mechanical roles of enamel and dentin may arise from their different compositions and internal structures, as revealed through scanning electron micrographs of enamel and dentin.

Keywords: Mechanical properties; compression tests; dentin; enamel; hardness tests.

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Conflict of interest statement

Declaration of conflicting interests: There is no conflict of interest regarding this manuscript.

Figures

Figure 1.
Figure 1.
Specimen preparation: (a) cross-sectioned after fixing a tooth within epoxy resin, (b) dimensions of enamel and dentin specimens, and (c) dimensions of ED specimens. ED: enamel–dentin. Here, P is load or force. Specimens were machine-cut and extracted along the direction of the force applied.
Figure 2.
Figure 2.
Cross-sectioned tooth specimen in epoxy resin for hardness test with measurement points.
Figure 3.
Figure 3.
Micro-load system used in compression test: (a) selectable grip on lower part of the jig that is installed with a load cell on the upper part of the jig; (b) compression test jig—a jig cover was installed to prevent the broken pieces from popping when the specimens reached their breaking points; (c) compression test was performed after placing the specimens on the lower jig and lowering the upper jig.
Figure 4.
Figure 4.
A typical stress–strain curve of the enamel, dentin, and ED specimens. ED: enamel–dentin.
Figure 5.
Figure 5.
Dental hard tissues: colored scanning electron micrograph (SEM) of the boundary between tooth enamel (top) and dentin (bottom). Enamel is the outer covering of the crown (visible part) of the tooth. It is the hardest substance in the human body, comprising rows of hydroxyapatite (calcium and phosphorus salts) embedded in a protein matrix. Dentin makes up the majority of the tooth. It comprises mineralized connective tissue. Magnification: 500× when printed 10 cm wide (permitted by http://www.sciencephoto.com). SEM: scanning electron micrograph.
See this image and copyright information in PMC

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