## 2 Materials and Methods  
The sectional method has been previously described by [PERSON] et al. [12,21] for evaluating the marginal gap: 60 typodont maxillary right first molars (FLUX 8634; Columbia Denttoform, Lancaster, PA, USA) were used. The CS group included 30 typodont teeth scanned with an intraoral scanner (CEREC(r) AC Omnicam; Dentsply Sirona, Milford, DE, USA), the finish line was marked, and the restoration was designed (CEREC(r) SW 4.5.2; Dentsply Sirona, Milford, DE, USA) and milled from zirconia-reinforced lithium silicate ceramic blocks (CELTRA(r) DUO, Sirona Dentsply, Milford, DE, USA) using a CAM milling unit (CEREC inLab MC XL(r); Dentsply Sirona, Milford, DE, USA) (Figure 1).  
The open system group included 30 typodont teeth which were scanned with an intraoral scanner (CEREC(r) AC Omnicam; Dentsply Sirona, Milford, DE, USA). The 30 scans were converted from RST files, which are specific for CEREC(r) software, to universal STL files, using a CEREC(r) Dongle, and data were imported to an open CAD system (EXOCAD(r) DentalCAD 2.2 Vallenta, Darmstadt, Germany). The finish line was marked, and the restoration was designed. Crowns were milled from zirconia-reinforced lithium silicate ceramic blocks, CELTRA(r) DUO (Sirona Dentsply, Milford, DE, USA), using a CAM milling unit (CEREC inLab MC XL(r); Dentsply Sirona, Milford, DE, USA).  
Specific parameters for all 60 crowns included in this study were identical, as follows: radial spacer--120 \(\upmu\)m; occlusal spacer--120 \(\upmu\)m; proximal contacts--25 \(\upmu\)m; radial minimal  
Figure 1: First maxillary right molar tooth and zirconia-reinforced lithium silicate crown.  
thickness--800 \(\upmu\)m; occlusal minimal thickness--1000 \(\upmu\)m; absolute marginal thickness--50 \(\upmu\)m; marginal ramp angle--45\({}^{\circ}\); marginal ramp width--150 \(\upmu\)m.  
All crowns were cemented with self-adhesive resin cement (Rely X U-200; 3M ESPE), while using a pressing machine Lutron Electronic Enterprise Co. Ltd FG-20 KG (Taipei City, Taiwan) which exerted a constant force of 50 Newtons on the model and crown at the time of cementation, in order to avoid the effect of diverse compressive forces on the marginal compatibility. At this point, 60 samples (30 for each group) were made up of a custom crown for the model being scanned and pasted into one unit. All units (crown and abutment) were cut by a precision saw (Isomet Plus cutting saw; Buehler), first from buccal to lingual then from mesial to distal, creating four samples from each unit (Figure 2):  
mesio-lingual (ML), disto-lingual (DL), disto-buccal (DB), and meso-buccal (MB). All specimens were evaluated by using a scanning electron microscope (JSM-IT100, JEOL, Peabody, MA, USA) at 250\(\times\) magnification in two regions of interest. Two parameters were measured in this study: first, in the vertical dimension (MG), which represents the micro gap between the restoration and the preparation; secondly, in the horizontal dimension (AMD), which represents the under- or over-extension of the restoration in relation to the finish line of the preparation (Figure 3).  
Statistical analysis was performed using the Statistical Package for Social Sciences for Windows Release 23.0 (SPSS Inc., Chicago, IL, USA).  
Independent-samples Mann-Whitney U tests were used for the comparison of fit between the production methods. A reliability test was performed by a BH-correct statistical test. The statistical significance level for this work was \(p\) <0.05.