## 2 Material and Methods  
### Fabrication of the Master Model, Definitive Casts, and Digital Models  
Fourteen polyetheretherketone (PEEK, US Korea, Seoul, Korea) cylinders with 5-mm diameter and 15-mm length were milled using an industrial computer numerically controlled (CNC) lathe (OC-24 BR-200, Ohmiya Machinery, Saitama, Japan) with a tolerance of less than 2 \(\upmu\)m. All the artificial teeth were removed from an acrylic maxillary model (D85 DP-500B, Nissin Dental Products Inc., Kyoto, Japan), and utility wax (Dental Utility Wax Rods Round, Kerr Corporation, Orange, CA, USA) was filled into the empty spaces. An impression of the model was made using high-viscosity (Exafine putty type, GC Corp., Tokyo, Japan) and low-viscosity polyvinyl siloxane impression materials (Aquasil XLV, Dentsply Sirona, York, NY, USA) with a metal stock tray (Coe Metal Impression Tray, GC America Inc., Alsip, IL, USA). After complete polymerization of impression materials, the tray was removed from the model, and epoxy resin (Polyurock, Cendres + Metaux,Biel/Bienne, Switzerland) was mixed according to the manufacturer's instructions, poured into the impression, and allowed to stand for 10 h to complete polymerization. The epoxy resin model was removed from the impression, and a hole of 5.5-mm diameter and 10-mm length was made at each tooth position using a carbide bur (HP701-012, Komet USA LLC, Rocky Hill, CT, USA) to receive the PEEK cylinder. The PEEK cylinders were fixed using autopolymerizing acrylic resin (Jet; Lang Dental Manufacturing Co. Inc., Wheeling, WV, USA), and roughly 5 mm of the 14 PEEK cylinders were extruded from the crest. Each cylinder was assigned the corresponding tooth number accompanied by the letter C (i.e., #17C, C means cylinders). In a pilot study, an intraoral scanner failed to differentiate each cylinder due to the identical configuration of PEEK cylinders; therefore, various irregular patterns, such as V, inverted V, and small oval circles, were engraved using a carbide bur (1.104.018, Komet USA LLC, Rocky Hill, CT, USA) around the cylinders to differentiate each cylinder (Figure 1). Conventional impressions of the master model were made using a low-viscosity polyvinylsiloxane impression material (Aquasil XLV) and a custom tray (Fastray, Bosworth Co. Evanston, IL, USA). Tray adhesive (VPS tray adhesive, Kerr, Orange, CA, USA) was applied and dried 5 min before the impression, and the tray was positioned for 10 min before removal from the master model. Type IV stone (MG Crystal Rock; Maruishi Gypsum Co. Ltd., Tokyo, Japan) was vacuum-mixed and poured into the impression following the manufacturer's instructions, and was removed from the tray after 1 h. A pilot study showed that the estimated sample size was more than 23, with \(\alpha=0.05\) and power of 95%. The procedure was repeated to fabricate 25 definitive casts, and these were assigned as Group CI (Figure 2). Digital scans of the master model were performed using an intraoral scanner (Trios 3, 3 Shape, Copenhagen, Denmark) to fabricate digital models. 3D calibration procedure preceded each scan using a black cylindrical calibration object supplied by the manufacturer. The scan sequence was conducted by following the manufacturer's instructions (Figure 3) without any scan spray application, and the acquired digital data were saved in a standard tessellation language (STL) file format. Twenty-five digital models were fabricated using the same method, and the digital models were assigned to Group ISO. A single operator ([PERSON]) performed all the calibration and digital impression procedures.