Figure 8. The applied force (solid line) and the tip displacement (dashed line) graphed as a function of time for a typical AFM indentation of hydrated intertubular dentin. In this example, the profile of the applied force was trapezoidal: a three-second loading phase, a three-second hold at maximum load, and a three-second unloading phase. At constant load, the indenter tip continues its inward displacement at a rate (dh/dt) that is approximated by the slope of the dashed line at the midpoint of the hold phase. The unloading rate is given by dP/dt. These factors are used to correct the AFM data for creep relaxation. In this example, the correction to the contact stiffness raises the Young’s modulus by about 20%.