In this study, the attrition wear, also called occlusal-contact-area wear, of human enamel was measured quantitatively with a computerized three-dimensional measuring technique over a period of four years. Tooth replicas from a clinical trial were used. A running-in wear period after restorative treatment, followed by steady-state wear, was suggested. The average steady-wear rate on occlusal contact areas was about 29 microns per year for molars and about 15 microns per year for premolars.