## 2 Materials and Methods  
### Sample Preparation  
Pilot experiments were conducted five times to determine the sample size and 12 samples were calculated using a power analysis software (G*Power v3.1.9.2, Heinrich Heine University, Dusseldorf, Germany) (actual power = 99.43%; power = 99%; \(\alpha\) = 0.05). To increase power, the number of samples presented in this study was determined to be 15.  
Figure 1 shows the experimental design. A maxillary resin typodont (AG-3 ZPVK, Frasaco GmbH, Tettnang, Germany) was prepared for a 3-unit FDP involving the first premolar and first molar. The margin was prepared with a depth of 1.2 mm in the chamfer form and the angle was set at 6\({}^{\circ}\). The prepared typodont was scanned using a desktop optical scanner (E1 scanner, 3 Shape, Kobenhavn, Denmark) and the scanned model was fabricated using a 3D printer (FS271M, Farsoon Technologies, Hunan, China) using Co-Cr materials. The metal model was then polished (Figure 2A).  
Figure 1: Experimental design.  
Figure 2: Scan process of model and design process of three-unit fixed dental prosthesis (3-unit FDP). (**A**) Metal model. (**B**) Scan process of model. (**C**) Virtual model. (**D**) Design process: Parameter setting of cement space. (**E**) Design process: Modification of prosthesis size and position. (**F**) Design process: Virtual 3-unit FDP.  
The 3-unit FDPs were fabricated by the in-lab (open type) and chairside (closed type) groups according to the digital workflow. The in-lab (open type) group used a partially digital workflow. An impression of the metal model was taken by simultaneously injecting light body impression materials (Aquasil Ultra Rigid, Dentsply Sirona, York, PA, USA) around the abutment along with heavy body impression materials (Aquasil Ultra Rigid, Dentsply Sirona) on a custom impression ray. Type IV stone (Fujirock, GC, Leuven, Belgium) was poured into the impression and stone casts were made. The stone casts were used to obtain a virtual model by using the desktop optical scanner (E1 scanner, 3 Shape) (Figure 2B,C). Prior to use, the desktop optical scanner was calibrated according to the manufacturer's recommendations. The acquired virtual models were transferred to the CAD software (exocad, exocad GmbH, Darmstadt, Germany), which was used to design the 3-unit FDPs (Figure 2D-F). In the CAD software, the cement space was set to 120 \(\upmu\)m from 1 mm above the preparation finish line (Figure 2D). The designed 3-unit FDPs were saved as standard tessellation language (STL) files. The STL files were loaded into a milling unit (EZIS HM, DDS, Seoul, Republic of Korea) and the 3-unit FDP was fabricated using a lithium disilicate block (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein). The milled 3-unit FDPs were crystallized according to the manufacturer's recommended settings by using a ceramic firing furnace (Multimat NTX, Dentsply Sirona) (Figure 3A).  
The chairside (closed type) group used a fully digital workflow. Anti-reflective powder with an approximate thickness of 2 \(\upmu\)m was uniformly applied to the metal model and the metal model was scanned using an intraoral scanner (CEREC Omnicam, Dentsply Sirona) according to the manufacturer's recommendations. One investigator (K.S.) performed a total of 15 scans with each intraoral scanner. The obtained virtual models were transferred to the CAD software (CEREC S/W 4.4.4, Dentsply Sirona) in order to design a 3-unit FDP. In the CAD software, the cement space was set to be the same as the in-lab (open type) group. The designed 3-unit FDPs were saved as STL files which were then loaded into a milling unit (CEREC MC XL, Dentsply Sirona) and fabricated using the same material as the in-lab (open type) group. The milled 3-unit FDPs were then crystallized (Figure 3B).