Determination of elastic modulus of dentin by small spherical diamond indenters

A nano-indentation test was applied to determine elastic modulus (E) and hardness (H) of dentin. Three spherical indenters with nominal radii of 20, 5 and 1 microns were used and load/partial-unload cycles were repeated. Each cycle provided E and contact pressure or Meyer's hardness. The plot of contact pressure versus penetration depth was converted into a normalized indentation stress-strain relationship, which was used to select the optimum maximum indentation force for each indenter. The results were compared with those determined by the conventional triangular pyramidal (Berkovich) indenter technique. The comparable E value, irrespective of radius, was 19.5-20.9 GPa and the 1 micron indenter was able to provide E values of peritubular (28.0 GPa) and intertubular dentin (14.9 GPa). The H values generated with the Berkovich indentation technique were comparable to those determined by the spherical indenter technique at indentation strains of 0.9 and 0.5 for the 1 and 5 microns indenters.