## 2 Materials and Methods  
The present study was conducted as in Figure 1. To determine the sample size, a pilot experiment was conducted five times using the same experimental method as that of the present study; based on the result of the pilot experiment, it was established using power analysis software (G*Power v3.1.9.2, Heinrich-Heine-Universitat, Dusseldorf, Germany) that there should be 15 samples (\(n\) = 15 per scanner; effect size (f) = 0.65; actual power = 99.16%; power = 99%; \(\alpha\) = 0.05). Figure 1: Experimental design. Since the present study obtained a conventional impression method with polyvinyl siloxane (PVS) (Aquasil Ultra; Dentsply Sirona, Bensheim, Germany) from the oral cavities of patients to produce reference casts, it was carried out after receiving the approval of the Institutional Review Board of the Kyungpook National University Dental Hospital (approval number: KNUDH-2019-02-02-02). The 10 participants were subjects who needed a single crown for ceramic prosthesis on the maxillary molar or premolar and the mandibular molar or premolar (premolar, 5; molar, 5). Of the participants, those who had poor oral health or who needed more than one crown were excluded. Impressions of the 10 subjects were taken from their oral cavities using a PVS impression (Aquasil Ultra; Dentsply Sirona, Bensheim, Germany) and a double-arch tray (Dual Arch Impression Tray; 3M, St. Paul, MN, USA). On the basis of these impressions, a type IV dental stone (FUGIROCK; GC, Leuven, Belgium) was used to produce reference casts (premolar, 5; molar, 5). All the reference casts were produced by a skilled dental technician (K.S.). The abutments in the reference casts were scanned using a contact 3D scanner (DS10, Renishaw plc, Gloucestershire, UK) (Figure 2). The abutments were scanned while a contact probe with a diameter of 0.5 mm was contacted lightly, moving upward at an interval of 200 \(\upmu\)m. Each abutment was scanned three times. To produce a high-definition reference model, the scanned files were merged after optimal alignment, using reverse engineering software (Geomagic Design X, 3D Systems, Rock Hill, SC, USA), and one CRM was produced for each reference cast (Figure 2). For accurate scanning, the scan files were obtained after the calibration of the equipment by an engineer from the scanner manufacturer. With the 10 types of CRMs (premolar, 5; molar, 5) obtained, the volume and area of the upper side of the abutments were measured based on their finish lines, and the results were as follows. Volume: premolar (84.2 \(\pm\) 13.6 mm\({}^{3}\)), molar (238.4 \(\pm\) 28.6 mm\({}^{3}\)); area: premolar (76.5 \(\pm\) 15.6 mm\({}^{2}\)), molar (165.6 \(\pm\) 18.6 mm\({}^{2}\)). Three types of intraoral scanner (Figure 3), including CS3600 (Carestream Dental, Atlanta, GA, USA), i500 (MEDIT, Seoul, Korea), and EZIS PO (DDS, Seoul, Korea), and one  
Figure 2: Procedure for evaluating 3D analysis. (**A**) Contact scanning procedure for CAD reference model (CRM). (**B**) CRM. (**C**) Scanning procedure for CAD test model (CTM). (**D**) CTM. (**E**) Superimposition of CRM and CTM. (**F**) 3D evaluation. laboratory scanner, E1 (3 Shape A/S, Copenhagen, Denmark), were employed (\(n=15\) per scanner) (Figure 2). First, the abutments were precisely scanned, and the adjacent teeth were scanned. Furthermore, for 3D analysis, they were extracted in a stereolithography file format and used as the CTM. The scanning accuracy analysis was performed using a 3D analysis software program (Geomagic control X; ver.2018.0.0, 3D Systems, Rock Hill, SC, USA). Based on the CRM, the CTM was superimposed (Figure 2). Optimal alignment was conducted by the following process: initial and best fit alignment. The sampling ratio was set to 100%, based on the CRM. According to the algorithm of the 3D analysis software program (Geomagic control X; ver.2018.0.0, 3D Systems, Rock Hill, SC, USA), the closest point-to-point among each point cloud of the CRM and the CTM was selected as the corresponding pairs.