Three-dimensional load analysis of indentation stimulators.

The properties of three types of indentation stimulators: filament indenters, a spring gauge indenter, and an electromechanical stimulator, were evaluated by actuating each device against a 3-direction load cell. The on-axis loads produced by filament indenters were independent of the degree of buckling. The off-axis loads produced by a filament increased with the degree of buckling of the filament, and had magnitudes that were up to 25% of the on-axis load. Repeated applications of a filament produced loads whose magnitudes were very consistent. Offsetting the handle of a filament indenter altered the magnitude and the direction of the off-axis load. Because these factors were poorly controlled in hand held trials, off-axis loads were more variable in hand held trials. The spring gauge stimulator was, when hand held, very susceptible to creating large off-axis loads. When the off-axis loads were large, the spring gauge indicator underestimated the true on-axis loads. The electromechanical stimulator produced loads with a very high degree of consistency and could be arranged so that it produced very small off-axis loads.