Abstract: A reciprocal sliding friction and wear tester was performed to investigate and compare the friction and wear behaviors of natural teeth of different ages sliding against titanium alloy under the lubrication of artificial saliva. The microstructures and worn surface morphologies of the tested teeth were observed with an optical microscope and co-focus laser scanning electron microscope. It was found that the friction and wear behaviors of the natural teeth of different ages were strongly dependent on the age, which was related to the different microstructures of the teeth at different ages. Namely, the early-stage permanent teeth showed similar friction and wear behaviors as the medium-stage permanent teeth, and the medium-stage permanent teeth had the best wear-resistance among the teeth of different ages. This was because the medium-stage permanent teeth had the most compact and strong microstructure, which contributed to preventing them from severe scuffing and abrasion in a long run. Contrary to the above, the primary teeth and later-stage permanent teeth had relatively fragile and weak microstructures, therefore they showed relatively poorer wear-resistance than the early-stage and medium-stage permanent teeth, owing to the liability to be scuffed and abraded. This accounted for the more severe scuffing and abrasion signs on the worn surface of the primary teeth and later-stage permanent teeth as compared to that of the early-stage and medium-stage permanent teeth as well.