## 2 Materials and Methods  
To simulate a clinically close setup, a partially edentulous maxillary model was used as an implant master model (IMM). The model shows a typical patient situation with one interrupted and one unilaterally shortened arch. The base plate (100 \(\times\) 100 mm) of the model is made of stainless steel, into which four steel tubes for implant placement (positions 16, 14, 25, and 26 of the Federation Dentaire Internationale [FDI]) were inserted. Four steel tubes for implant placement (positions 16, 14, 25, and 26 of the Federation Dentaire Internationale [FDI]) were inserted in the stainless steel base plate (10 \(\times\) 10 cm) of the IMM, and Straumann RN Standard Plus implants (Straumann, Freiburg, Germany) were adhesively luted in the tubes (14 mm length, 4.8 mm diameter; Galvano AGC-Cem adhesive, Wieland-Dental, Wurzburg, Germany). Two references cubes (RC, perpendicular to each other) were inserted in FDI positions 18 and 23. The basic structure of a partially dedentulous upper was modelled of pink-colored methyl methacrylate (PalaXpress, Kulzer, Hanau, Germany; Figure 1). To determine the implant positions, the IMM was digitized using a coordinate measuring machine (CMM, Thome Rapid, Thome precision, Messel, Germany, accuracy 2.2 \(\upmu\)m) with the corresponding software Metrolog (Metrologic Group, Meylan, France). Therefore, the upper surface of the individual scanbodies were touched and defined as a plane. Then, the lateral surfaces of the scanbodies were touched and defined as cylinders. The known length of the scanbodies made it possible to transfer the plane of the surface to the implant-abutment interface point by means of a parallel shift. To determine the length of the scanbodies precisely, they were also measured with the CMM (Thome Rapid, Thome precision, Messel, Germany) during preliminary tests. The defined plane on the scanbodies as well as the definiton of the cylinder also made it possible to determine the angulation of the scanbodies. The same applies to the rotation, which could be defined on the basis of another flat surface on the outer surface of the cylinder of the scanbody. Based on the reference cube (RC; FDI 18) on the IMM, a coordinate system was defined as reference. Scan data were exported as a standard tessellation language (STL) file format, serving as a reference file. Four intraoral scanbodies (ISBs; N1410, Medentika, Hugelsheim, Germany) were screwed in the implants (15 Ncm) of the IMM for the digital impressions. The H1410 ISB consists of a cylindrical titanium base and a flattened plane in the upper part. Scans were performed using three different IOS families: True Definition Scanner (3M, St. Paul, MN, USA), which is based on active wavefront sampling; the TRIOS  
Figure 1: Implant master model (IMM) with two reference cubes and final setup with inserted scan bodies (FDI 16, 14, 25, 26). family (3 Shape, Copenhagen, Denmark) based on confocal laser scanning microscopy; and the Sirona CEREC Omnicam/Primescan family (Sirona, Bensheim, Germany) with an optical triangulation technique. Primescan additionally uses confocal microscopy [28; 29] as a second acquisition principle. The scanners used in the corresponding software versions are listed in Table 1.  
Two trained and calibrated examiners ([PERSON] and [PERSON]) performed 10 full-arch scans using the calibrated scanners and followed the scanning paths, recommended by the different manufacturers, which were as follows: scan started at the occluso-palatal surfaces of the right molar in the maxillary (including the RCs), moved towards the second quadrant constantly including the palatal surfaces, then again to the RCs, and to the occlusal surfaces, returning to the buccal side. It was of particular importance that both examiners had an identical level of training in scanning. Both were in the same period after their exams and were trained on all devices.