NANOINDENTATION OF TOOTH TISSUES - Nanoindentation with Biological Applications - page 261

Porosity
Figure 8-9. Nanoindentation elastic modulus against the mineral porosity of WSL
sample.

and calculated from the gray value of micro-CT images. 83 By taking the
mineral density of sound enamel as 3.0 g/cm 3 , the porosity of every

indented lesion point can be calculated with the equation: Porosity =
ρ lesion /ρ sound , and correlated with the elastic modulus at that point
( Fig. 8-9 ) . A good exponential relationship was found and the result can
be related to Rice's minimum solid area model for porous materials. 84 In
addition, recent high resolution electron microscopy observation
provided direct evidence on the dissolving and pore formation of enamel
HAP crystals. 85
Deterioration in the mechanical properties of dentin is not only
known as an early sign of carious demineralization in dentin, but of
clinical relevance for caries assessment and treatment selections. The
nanoindentation technique enables testing of carious dentin in a hydrated
state, which is of particularly significance as the hardness and elastic
modulus of carious dentin have been shown to increase significantly with
dehydration, and a hydrated condition is considered more clinically
appropriate. 72 This difference was not evident using traditional
approaches such as Knoop indentation, which depends upon visual

ρ sound