## 1 Introduction  
Digitalization is a recent trend in dentistry, characterized by the development of digital models to replace plaster casts. Many researchers have attempted to minimize the need for conventional laboratory work by enhancing the accuracy of digital models. Thus, numerous previous studies attempted to assess the accuracy of digital models produced in various ways. However, the accuracy evaluation of digital models is challenging when compared to the actual dental arch. In previous studies, researchers set the dental cast model or the extraoral optical-scanner-generated digital model as a gold standard to which they compare digital models obtained with different methods to evaluate the accuracy [1; 2; 3; 4]. This is because there is no proper landmark for measuring true values in the oral cavity, and there is no suitable method to specify the same landmark point on a replicated digital model [5]. For the full dental arch, extraoral desktop scanning of plaster models is a clinically applicable method with acceptable stability and accuracy [6]. An intraoral scanner is advantageous in that it directly scans a patient's dental arch with no lab work involved, yet the problem of distortion in scans of the full dental arch has not been solved [7]. Moreover, for both extraoral and intraoral optical scanners, light sources have difficulty reaching areas such as proximal undercuts or complex-angled surfaces, meaning that some areas can lack information [8]. These methods generate a digital model through additional data processing steps, and the errors encountered during this process affect the accuracy of the final stereolithography (STL) data [9]. Another emerging method is the use of cone-beam computed tomography (CBCT) to obtain a digitized model by scanning an impression or plaster model in a special image acquisition mode [10]. This method is advantageous in that an additional machine is not required for digital model generation, the scanning time is relatively short, the patient experiences no discomfort, and the characteristics of the X-ray penetrance prevent information loss regardless of the shape of objects such as undercut, in contrast to direct optical scans of the patient's mouth [11; 12; 13]. Digital Imaging and Communications in Medicine (DICOM) data that are obtained from CBCT devices can also be converted into STL data using various software [14; 15; 16]. Thus, the performance of the conversion software also affects the accuracy of the digital models. As various methods of obtaining digitized models have been developed, many researchers have investigated whether various scanning methods are sufficiently accurate. As stated above, there are several obstacles in assessing the accuracy. First, acquiring precise and reproducible measurements of reference models and digitized models is a challenging process. The common reference points for the measurements are cusp or fossa of the crown, which could be differently pointed on each experiment with low intra- and interobserver reliability [5; 17; 18; 19]. Setting the appropriate reference points is the first step in obtaining reliable data for comparison of accuracy. Second, most studies have primarily involved comparative analyses of digitized data and conventional plaster models or data obtained with optical scanners [1; 2; 8; 20]. Since the digital model generation procedure is based on an impression or plaster model, which already involves distortion, the accuracy of the overall digital model should be evaluated based on the gold standard value obtained from the patient's actual dental arch. To obtain this gold standard value with high accuracy, coordinate measuring machines (CMMs) have been introduced in dentistry [21]. CMMs are widely used in industrial applications and are known to be precise and able to be used in the dental field, which requires micro-unit accuracy. This machine contacts the desired point with a probe and records its coordinates.