Anelastic Phenomena in Human Dentin below Room Temperature

The work describes the anelastic behaviour of human dentin below room temperature. Human molars, extracted from individuals as part of their dental treatment, were cut to obtain bar-shaped samples for mechanical spectroscopy (MS) experiments. Repeated cooling-heating cycles in the range 300-100 K have been carried out on the same samples. In the cooling stage of the first cycle Q^-1 exhibits a very broad maximum due to a series of phase transformations involving water present in the pores, in the interstices between fibres, between fibrils and inside collagen triple helix. The formation of ice I_h produces permanent damages to the dentin structure (rupture of fibres and fibrils) leading to a decrease of maximum intensity in the following cycles. In the heating stage of all the cycles two maxima, M1 and M2, have been observed around 155 K and 178 K. M1 is due to the transformation of low-density amorphous (LDA) ice into ice I_C while M2 to that of ice I_C to ice I_h. Above 200 K, Q^-1 progressively increases with lower damping values in the cycles after the first one. Dehydrated samples do not exhibit the aforesaid anelastic phenomena confirming that their origin is connected to water and its transformations.