Wear and marginal quality of 14 mesio-occlusodistal amalgam restorations (Dispersalloy) were quantitatively analyzed in this in vivo study. Wear rates, measured as maximu m vertical loss of substance in the occlusal contact area, were 41, 50, 57, 79, 82, 123, 165, and 215 um after 1, 2, 3, 6, 9, 24, 36, and 48 months, respetively. In the contact-free occlusal area an expansion of 2 to 9 um was recorded. The micromorphology of the tooth-amalgam interface significantly changed within the first 9 months after restoration placement. The percentage of marginal opening increased from 91% to 100%, marginal restoration fracture from 49% to 89% and underfilled margin from 50% to 78%. Amalgam restorations have clinically proved successful despite their poor marginal adaptation and their inferior wear resistance compared to enamel. Thus, the wear resistance of amalgam substitutes, preferably metal-free, tooth-colored restorative materials, would not necessarily have to exceed that of amalgam to replace it. The wear data generated may serve as guiding figures in the development of amalgam substitutes.