## 2 Materials and Methods
Using this design, twenty-four anatomic copings were fabricated using cobalt-chromium bonding alloy for the manufacturing of removable and fixed restorations by selective laser melting (SLM) using the same powder used for SLS copings (Starbond CoS Powder 30, S&S Sheftner GmbH, Mainz, Germany) free of beryllium and nickel. Laser power was 80 W, powder layer 20 \(\upmu\)m, under-protected N2 atmosphere \(<\)0.3 L/min, using Mysint 100 (Sisma, Piovene Rocchette, Italy). The other set of twenty-four copings were milled from a cobalt-chromium metal disc (White Peaks Dental Systems GmbH & Co. KG, Essen, Germany) using a 5-axis milling machine (Datron D5, Datron AG, Muhltal-Traisa, Germany) and the same design. Relief-firing was performed for SLS and SLM copings (Figure 6): They were heated to 450\({}^{\circ}\) within 60 min, held at this temperature for 45 min, heated to 800 \({}^{\circ}\)C within 45 min, kept for 60 min, then slowly cooled, under nitrogen atmosphere. SLS and SLM frameworks were placed on the building platform with the occlusal face parallel with and towards the plate, and the post-processing step was performed with the copings still attached to the plate. For porcelain veneering, the same design was made for all ninety-six copings, which were scanned with a D700 3D scanner (3 Shape, Copenhagen, Denmark). All copings were prepared for veneering by sandblasting (75 \(\upmu\)m alumina particles), degreased using steam, and dried. Opaque firings were conducted after two applications of Opaquer paste IPS InLine System (Ivoclar Vivadent, Schaan, Principality of Liechtenstein), following manufacturers indications. Ceramic veneering was made by over-pressing, to eliminate the subjectivity and variations generated by conventional technology. For that, veneering copings were obtained by milling of Harvest ZCAD Wax Press (Harvest Dental Laboratory Products) using Zenotec (Wieland Dental + Technik GmbH & Co. KG, Pforzheim, Germany) unit. These patterns were attached to previously prepared frameworks, sprues were attached, and the weighted ensemble was invested in specific material PressVEST Speed (Ivoclar Vivadent, Schaan, Principality of Liechtenstein). After preheating the molds at 850 \({}^{\circ}\)C for 75 min, the ceramic (IPS InLine PoM, Ivoclar Vivadent, Schaan, Principality of Liechtenstein) was over-pressed using the specific program of the furnace Programat EP 3010 (Ivoclar Vivadent, Schaan, Principality of Liechtenstein). The crowns were divested, processed, and glazed according to the material's recommendations. Figure 6: SLM frameworks after relief firing. The initial and final gap was evaluated to establish if and how veneering firings affect internal and marginal adaptation. Measurements were made using silicon replicas for each framework before ceramic opaquer appliance and after glazing for each crown. Low viscosity silicone used for this purpose Black Fit Checker (GC Corporation, Tokyo, Japan) was inserted inside frameworks and crowns to mimic the cement, under constant pressure, until set. This silicone layer was placed between a layer of light-consistency silicone Oranwash L ([PERSON], Badia Polesine, Italy) and a putty Zetalabor ([PERSON], Badia Polesine, Italy). Silicone blocks obtained have been sectioned and photographed under an optical microscope (Leica DM500, Leica, Wetzlar, Germany) with a hundred micron scale for image calibration at 20\(\times\) magnification. ImageJ software was used for measurements after calibration using the scale (Figure 2). For the gap measurements, nine different points were analyzed for each specimen, for the following sites: marginal gap (MG), cervical gap (CG), axial internal gap in the middle of axial wall (AG), and occlusal internal gap wall on cusps and in the central fossa (OG).