## 2 Materials and Methods
### Design and Fabrication of Ceramic Crowns  
A previous study reported that a clinically acceptable marginal gap must be less than 90 \(\upmu\)m when the crown is processed using a CAD/CAM system ([PERSON] et al., 2017). Hence, in the software for each system, the setting values of the cement space were determined to enable the fabrication of crowns with a marginal gap >90 \(\upmu\)m. Based on the preparatory experiment, the setting values of the cement space for the CEREC system, EZIS system, and Carestream system were 80 \(\upmu\)m, with an additional 60 \(\upmu\)m on the occlusal surface. Using the CEREC software (CEREC S/W 4.4.4; Dentsply Sirona, York, PA, USA, 2017) the crown was designed as follows: the patient information was entered and then the teeth to be restored, the kinds of prostheses, and the materials to be used were selected (Figure 1A). Next, the inserting axes without margins or being undercut were then determined (Figure 1B). After the design of the crown was selected in the library (Figure 1C), the location and size of the crown were adjusted (Figure 1D). Next, the setting values of the following input variables were given (cement space, 80 \(\upmu\)m; Figure 1E). At last, the location and size of the crown inside the lithium disilicate ceramic CAD block (IPS e-max CAD LT; Ivoclar Vivadent AG, Schaan, Liechtenstein, 2017) were checked using the CAM software prior to the fabrication of the crown (Figure 1F). The IPS e-max CAD block was processed using a CEREC MC XL milling device (Dentsply Sirona, Bensheim, Germany, 2017), and the milled crown was crystallized using a Programat P300 ceramic kiln (Ivoclar Vivadent AG, Schaan, Liechtenstein, 2017), as per the manufacturer's instructions. Regarding the EZIS software (EZIS VR 1.4.2.14; DDS, Seoul, Korea, 2017), the same procedure was performed to create the crown (Figure 2). The ceramic crown was fabricated from the lithium disilicate ceramic CAD block with an EZIS HM milling device (Digital Dentistry Solution, Seoul, Korea, 2017). It was then fired using the same procedure as with the CEREC system. Regarding the Carestream system, the crown was designed unlike the other two systems described above; the steps in Figure 3A were carried out with the dental CAD software (Exocad Chairside; Exocad GmbH, Darmstadt, Germany, 2017). In addition, the steps in Figure 3B-E were conducted using the crown-design feature of dental CAD software (Exocad Chairside). In these steps, all input variables were identical to the two systems discussed above. At last, the size of the crown inside the block was checked and the location was adjusted using the CAM software (CS Restore; Carestream Dental, Atlanta, GA, USA; Figure 3F). Next, the ceramic crown was fabricated from an IPS e.max CAD block using a CS3000 milling device (Carestream Dental, Atlanta, GA, USA, 2017). The crystallization step was identical to that of the previous two systems. The milling devices of the CEREC and EZIS systems, shown in Table 1, allow simultaneous processing of the inside and outside of the ceramic crown by the two milling burs. In contrast, the milling device of the Carestream system permitted milling of the inner and outer sides using one milling bur on both sides. Figure 1: Crown design process using a computer-aided design and manufacturing software with the CEREC system. (**A**) Definition of a prosthesis (tooth selection, material selection, etc. ); (**B**) margin setting; (**C**) design suggestions; (**D**) design modification of the prosthesis (size, position, etc. ); (**E**) parameter setting; (**F**) confirmation of the size and position in the block for milling. Figure 2: Crown design process using computer-aided design and manufacturing software with the EZIS system. (**A**) Selection of teeth to be restored; (**B**) design of margins and insertion axes; (**C**) selected crown from the proposed library; (**D**) crown modeling; (**E**) numerical values as parameters; (**F**) crown alignment for milling.