Temperature dependence of water transport into the mineralized matrix of freeze-dried human dentine.

Ten dentine sections cut perpendicular to the dentinal tubules from human mature non-carious third molars, were freeze-dried and then rehydrated by immersion in water at four temperatures, 10, 25, 40 and 70 degrees C. The uptake of water by the sections was assessed as a function of rehydration time. The data were analysed using a theoretical model in which the uptake is ascribed to two processes. The first is capillary suction of water into the dentinal tubules, the second is the diffusion of water from the two faces of the section into the mineralized matrix. By fitting theory to experiment the diffusion coefficient of water in intertubular dentine at the different temperatures was found. Using the Arrhenius relation the activation energy of diffusion of water in intertubular dentine was calculated as Ea = 29.5 +/- 2.2 kJ/mol, which is of the order of the strength of a hydrogen bond. Transport of water in the mineralized matrix during rehydration is thus most likely a hopping of water molecules along the surfaces of the collagen and/or mineral, each jump involving the breaking of one hydrogen bond.