Resonant ultrasound spectroscopy measurements of the elastic constants of human dentin

The technique of resonant ultrasound spectroscopy (RUS) was used to measure the second-order elastic constants of hydrated human dentin. Specimens were placed between two transducers, and the resonant frequencies of vibration were measured between 0.5 and 1.4 MHz. The elastic constants determined from the measured resonant frequencies in hydrated dentin exhibited slight hexagonal anisotropy, with the stiffest direction being perpendicular to the axis of the tubules (E11=25.1 GPa). This hexagonal anisotropy was small (E33/E11=0.92), and almost disappeared when the specimens were dried. In addition, there was a pronounced anisotropy in the Poissonʹs ratio of wet dentin: ν21=0.45; ν31=0.29. With drying in air, this anisotropy vanished: ν21=ν31=0.29. The isotropic Youngʹs modulus of dried dentin was 28.1 GPa. RUS shows promise for determining the elastic constants in mineralized tissues.