Study on Tribological Behavior of Human Enamel Sliding against Various Counterparts under Lubrication of Artificial Saliva

The tribological behaviors of human tooth enamel sliding against human tooth enamel, titanium alloy, and pure titanium, under the lubrication of artificial saliva, were investigated and compared by conducting interval reciprocal friction and wear testing on a ball-on-flat test rig. The worn surface morphologies were observed on an optical microscope and a coincident focus laser-scanning microscope. It was found that the flat enamel specimen sliding against the spherical counterparts made of human tooth enamel, titanium alloy, and pure titanium had stable friction coefficients of 1.00, 0.92, and 0.87, respectively. It showed differences in the friction and wear behavior and the worn surface morphology, depending on the spherical counterparts. Namely, the worn surface of the enamel sliding against the spherical enamel was characterized by delamination and slight abrasion, and the enamel rods were visible on the thereon. Some ploughs, delamination scars, and enamel rods were observed on the worn enamel surface sliding against the titanium alloy counterpart, while transferred Ti film was formed on the worn enamel surface sliding against pure Ti counterpart. In terms of the evolution and stable value of the friction coefficient and the worn surface morphology and wear scar depth, the enamel/titanium alloy pair was similar to the enamel/enamel pair.