Impact of parameter settings on normal force and gap height during tribological measurements

• Tribological surface affected friction coefficient.
• Normal force and gap height fluctuation were affected by instrument parameters.
• A data screening protocol was developed to mitigate variations in normal force.
• Proper selection of measurement parameters is critical to obtain reproducible data.

There has been increased interest over the past decade to use soft tribology to mimic conditions in the oral cavity. Tribological measurements in these studies have been performed on a variety of instruments, both commercial and custom-made. While the effects of tribological surface characteristics (e.g. roughness, modulus, hydrophobicity) on tribological measurements have been examined, there has been little study of measurement variability due to differences in tribometer settings. Therefore, this study examined the effect of different tribometer measurement parameters on the magnitude and fluctuation of normal force, gap height, and friction coefficient. The instantaneous values of normal force and gap height, and the extent of fluctuation of those measurements, were affected by multiple instrument parameters. Friction coefficient values were not significantly affected by instrumental parameters; however, fluctuations in normal force and gap height can contribute to data variation, reducing measurement precision and adding confounding factors to data.