The local Young modulus of dry dentin viewed as a hierarchical composite was measured by nano-indentation using two types of experiments, both in a continuous stiffness measurement mode. First, tests were performed radially along straight lines running across highly mineralized peritubular dentin sections and through less mineralized intertubular dentin areas. These tests revealed a gradual decrease in Young's modulus from the bulk of the peritubular dentin region where modulus values of up to similar to 40-42 GPa were observed, down to approximately constant values of 17 GPa in the intertubular dentin region. A second set of nano-indentation experiments was performed on the facets of an irregular polyhedron specimen cut from the intertubular dentin region, so as to probe the modulus of intertubular dentin specimens at different orientations relative to the tubular direction. The results demonstrated that the intertubular dentin region may be considered to be quasi-isotropic, with a slightly higher modulus value (similar to 22 GPa) when the indenting tip axis is parallel to the tubular direction, compared to the values (similar to 18 GPa) obtained when the indenting tip axis is perpendicular to the tubule direction. (C) 2010 Elsevier Inc. All rights reserved.