NANOINDENTATION OF TOOTH TISSUES - Nanoindentation with Biological Applications - page 254

from chewing forces especially the high localized contacts from
asperities or small hard particles trapped between teeth. Also, sliding
wear between teeth and food particles may introduce high local tensile,
compressive and shear forces around sliding contact area. This
reversible, inelastic property may be vital to limit damage accumulation
and prevent excessive wear in enamel.

3.5. Nanoindentation measurements on dentin

Most nanoindentation investigations on dentin have concentrated on
the measurement of elastic modulus and hardness with respect to
its microstructure and composition. Nanoindentation allows for the
measurement of the highly calcified peritubular dentin and the
intertubular dentin separately, demonstrating the structural dependence
of dentin mechanical behavior. Data on the mechanical properties of
dentin in both permanent and primary teeth based on nanoindentation
investigation are summarized in Table 8-3 .
From these investigations, we may conclude firstly that dentin is an
anisotropic material and nanoindentation elastic modulus and hardness of
dentin are microstructurally dependent. As with enamel, the mechanical
properties of the dentin are larger when applied loads are parallel to
tubule directions compared to orthogonal directions. 59 Intertubular dentin
has hardness and elastic modulus of 0.51 1.3 GPa,

respectively, but values decrease with proximity to the pulp. 60 In
contrast, the more mineralized structure of peritubular dentin not only
has greater hardness and elastic modulus, but also is invariant with
respect to intra-dentin position. Overall the outer dentin has higher
hardness and elastic modulus compared to the inner dentin, 61,62 which
may be due not only to the changes in the mechanical properties of
intertubular dentin, but as a consequence of thicker peritubular dentin
and fewer tubules. 61
Secondly, primary dentin is mechanically inferior to the permanent
dentin, which has been shown with nanoindentation tests by Mahoney
et al . 34 and Poolthong. 36 This is because the dentin of primary teeth is
less calcified than the dentin of permanent teeth. 63,64 And lastly, changes

± 0.02 and 21.1 ±