Nanoindentation in teeth: influence of experimental conditions on local mechanical properties

The influence of various experimental conditions on the elastic modulus and hardness of human intertubular dentin was studied using instrumented nanoindentation at room temperature. The conditions studied were: dry (chemically dehydrated) versus wet (prepared and nanoindented under Hank's balanced salt solution (HBSS)), the influence of long-term storage under HBSS at ca. 4°C and the influence of deep-freezing under dry and wet conditions. The reversibility of chemical dehydration and the consequences of multiple deep-freezing cycles were also investigated. Two premolars of a 12-year-old human male were chosen for evaluation. The absolute values of the mechanical properties differed by a factor of ∼2 and ∼3 between dry and wet states, whereas trends were conserved. Deep-freezing wet dentin samples weakened their mechanical properties by 20–28%, whereas dehydrated samples suffered no damage. This may be due to mechanical damage via the volume increase in water freezing inside the tubules.