Scanning electron microscopy was used to compare the marginal gaps of restorations milled by machinable ceramic systems to the marginal gaps of conventional laboratory-sintered ceramic restorations. For occlusal surfaces, the average marginal gap was 80 um for both laborato ry- and Celay-produced inlays. The mean gap was 200 um and 170 um, respectively, for Cerec T (turbine motor) and Cerec EM (electric motor) inlays. For approximal boxes, the average marginal gap was 100 um for inlays produced with conventional laboratory-sintering techniques, 80 um for Celay restorations, and 280 um for the Cerec T restorations, and 260 um for Cerec EM-machined inlays. The ceramics used, as well as the different systems themselves, can influence the results and the clinical outcome of the restorations.