Microindentation in bone: hardness variation with five independent variables.

Microindentation is an investigational tool often used to determine hardness and other derived material properties of the material bone. This study explored the variation of microindentation hardness results with five independent variables. The variables were: applied mass, dwell time, drying time, time between indentation and measurement, and distance between the center of an indentation and the edge of other indentations and pores. These variables were selected because they represented a reasonable range of specimen investigational steps. We also investigated the cross sections of typical indentation residual impressions to determine the degree of material pile-up at the edges of the impressions. We found that microindentation hardness varied with applied mass and with distance between the indentation and neighboring indentations and pores but not with the other variables. Our recommended minimum applied mass is 0.10 kg versus a previously published value of 0.05 kg. We also found no discernable material pile-up at the residual impression edges, in contrast to reports of others.