The Mechanical Properties of Human Dentin: a Critical Review and Re-evaluation of the Dental Literature

Abstract

The past 50 years of research on the mechanical properties of human dentin are reviewed. Since the body of work in this field is highly inconsistent, it was often necessary to re-analyze prior studies, when possible, and to re-assess them within the framework of composite mechanics and dentin structure. A critical re-evaluation of the literature indicates that the magnitudes of the elastic constants of dentin must be revised considerably upward. The Young's and shear moduli lie between 20-25 GPa and 7-10 GPa, respectively. Viscoelastic behavior (time-dependent stress relaxation) measurably reduces these values at strain rates of physiological relevance; the reduced modulus (infinite relaxation time) is about 12 GPa. Furthermore, it appears as if the elastic properties are anisotropic (not the same in all directions); sonic methods detect hexagonal anisotropy, although its magnitude appears to be small. Strength data are re-interpreted within the framework of the Weibull distribution function. The large coefficients of variation cited in all strength studies can then be understood in terms of a distribution of flaws within the dentin specimens. The apparent size-effect in the tensile and shear strength data has its origins in this flaw distribution, and can be quantified by the Weibull analysis. Finally, the relatively few fracture mechanics and fatigue studies are discussed. Dentin has a fatigue limit. For stresses smaller than the normal stresses of mastication, approximately 30 MPa, a flaw-free dentin specimen apparently will not fail. However, a more conservative approach based on fatigue crack growth rates indicates that if there is a pre-existing flaw of sufficient size (approximately 0.3-1.0 mm), it can grow to catastrophic proportion with cyclic loading at stresses below 30 MPa.

Influence of material thickness on fractural strength of CAD/CAM fabricated ceramic crowns

“…In this study, dies with an E-Modulus of 2.5 GPa were fabricated with SLA technology. Compared to the E-Modulus of human dentine, reported to be between 7 and 13 GPa, these values are very low 16) . There is one study in literature showing the fracture resistance of all-ceramic crowns depending on the E-Modulus of the underlying supporting structure 17) .…”

The mechanical properties of human dentin for 3-D finite element modeling – numerical and analytical evaluation

“…The elastic properties of dentin influencing the tooth strength are usually described as stiffness including Young's modulus, shear modulus and Poisson's ratio. 14 The dentin microstructure, in combination with the whole tooth geometry, causes considerable variations in the results of experimental measurements of the dentin properties. 11,14 Dental models, like other models from the fields of biology or medicine, have a complex geometry.…”

“…14 The dentin microstructure, in combination with the whole tooth geometry, causes considerable variations in the results of experimental measurements of the dentin properties. 11,14 Dental models, like other models from the fields of biology or medicine, have a complex geometry. However, their geometry is relatively easier nowadays thanks to 3D scanners (micro-CT and CT), which offer an easy and fast way to build virtual geometry in any computer-aided engineering (CAE).…”

“…11 The dentin structure was assumed to be a transversely isotropic medium with one axis of symmetry, parallel to the direction of the dentinal tubules. 14,15 In this case, the micromechanical model used for homogenization was a unidirectional structure with long cylindrical voids embedded in an isotropic matrix. The micromechanical model allowed the strain concentration tensor and corresponding effective stiffness tensor (material properties) of the dentin structure to be determined according to Luciano and Barbero: 10 Where: P is a 4 rank tensor, which describes the geometry of the voids, microstructures, and the distribution of the voids, V f the volume fraction of the voids (lumen tubules), C f , C ms the 4 rank stiffness tensors of the voids (lumen tubules) and matrix (dentin), both isotropic.…”

Nanoindentation in teeth: influence of experimental conditions on local mechanical properties

“…Although the penetration depth of nanoindentation is small (< 1 µm); the mechanical properties thus obtained are assumed to be representative of the whole sample and are comparable to one of the most accurate ways of determining elastic constants of a material, i.e. sonic measurements [6]. Nanoindentation is a versatile, powerful and highly suitable technique for testing biomaterials, mainly because there is no need of vacuum condition and near in vivo condition can be attained quite easily.…”