## 1 Introduction  
The introduction of dental computer-aided design and computer-aided manufacturing (CAD-CAM) technology has led to a decrease in practitioner errors as well as material failures [1; 2]. In addition, production efficiency is greatly superior with CAD-CAM, compared to other existing methods [3]. The CAD-CAM process produces prostheses through scanning, CAD, and then CAM processes. The development of intraoral scanners and their combination with dental CAD-CAM systems has made it possible for all prosthesis production to be performed chairside [4; 5]. Since a chairsideCAD-CAM process does not need a working model and involves a shorter prosthesis processing and postprocessing time, a prosthesis can be produced and provided to a patient more rapidly. In addition, since zirconia requires time for postprocessing sintering [6], lithium disilicate is more commonly used for chairside production [7]. In addition, previous studies have shown that lithium disilicate crowns have a higher survival rate than feldspathic porcelain and alumina-oxide crowns do [8]. To further improve chairside CAD-CAM systems (by enhancing their accuracy and production speed), the development of intraoral scanners, CAM equipment, and materials is ongoing [9]. CAM processes are classified as either subtractive or additive manufacturing [10], but milling (a subtractive process) is actually used as a CAM process. In fact, milling is the most commonly used manufacturing process. For CAM, a five-axis milling unit can produce prostheses more accurately than a four-axis machine can [11; 12; 13]. With a five-axis milling machine, it is possible to mill pointed angles more accurately, given that a wider range of milling with a greater number of axes relative to the four-axis can be used [11; 14]. With a five-axis milling machine, the contact point between the tool and the prosthesis to be milled can be controlled, thus realizing better control of the milling conditions. However, somewhat more time is required to complete machining when using a five-axis milling unit [11]. Accordingly, for chairside CAD-CAM, the use of a four-axis milling unit is preferred to keep the chairside time within a clinically acceptable range. Several studies have evaluated the impact of the use of a chairside four-axis milling unit on the inner surface of the prosthesis [11; 12]. To the best of our knowledge, however, there have been no studies that have evaluated trueness according to region. Already, as a result of many preceding studies, chairside CAD-CAM production of prostheses is clinically practical [2; 15; 16; 17; 18; 19; 20]. [PERSON] [15] compared the fit of prostheses produced by a chairside CAD-CAM process to those produced by a laboratory (CAD-CAM) process. The prosthesis produced by the chairside process had a superior fit. [PERSON] [16] compared the fit of prostheses produced by a chairside (CAD-CAM) process to those produced by a laboratory (hot-press) process using a lithium disilicate material. The crown produced by the chairside process had a clinically acceptable fit. In a three-year clinical evaluation, [PERSON] [17] predicted the growth of chairside CAD-CAM as an alternative to prosthetic therapy, given a crown survival rate of 97.0%. Three-dimensional (3D) evaluation is often applied to determine whether mass-produced products have been accurately produced by manufacturing processes [21; 22; 23]. This can save time compared to visual examinations, [21] and an accurate analysis can be conducted with the development of a scanner [9]. Visual examinations require more time because human errors can occur and given that the evaluation is done by hand. In addition, due to advances in scanning technology, very precise scanning (<10 \(\upmu\)m) can be obtained, and accurate analysis is possible. Likewise, given the take-up of CAD-CAM techniques in dentistry, three-dimensional data have been evaluated in numerous studies [5; 24; 25; 26; 27; 28].