## 2 Materials and Methods  
A gypsum dental model type 1 with missing tooth #36 and the antagonist dental model were prepared for the study. An implant analog (standard platform, MIS) was embedded in the agonist model, replacing the missing tooth #36. A gingival mask was used to ensure the emergence profile was optimally contoured. The scan post (standard, Sirona) was inserted on an implant analog and tightened to 30 Ncm using the manufacturer's torque driver (short driver for 0.05-inch hex, MIS), followed by screwing the scan body (Sirona) on it. The model and the antagonist were scanned using an intraoral scanner (CEREC Omnicam Scanner; Dentsply Sirona, CEREC SW 4.6.1). This was converted to a 3-dimensional (3D) virtual model (CEREC AC software 4.6.1; Dentsply Sirona). This substructure was chosen instead of zirconia crown design to match the height settings of the SEM imaging JSM-IT100. The zirconia substructure design and the finish line marking of the model for 25 meso blocks (inCoris ZI meso F2 L, Dentsply Sirona) were planned using CEREC AC software 4.1. The CAD/CAM parameters of zirconia substructure were shoulder width 100 \(\upmu\)m, telescope angle 7, radial minimum thickness 500 \(\upmu\)m, and occlusal minimum thickness 500 \(\upmu\)m.  
A milling unit (CEREC MC XL; Dentsply Sirona) was used for CAM processing of the designed zirconia substructure. Milling of each sample from meso blocks was completed in approximately 17 min. At the end of milling, the system transferred the restoration details to SpeedFire for the firing cycle by sintering for 50 min in a furnace (CEREC SpeedFire; Dentsply Sirona). The surface of the zirconia substructures was polished with HP polishers (CEREC KIT2 HP polishers, EVE Diacera). Each sample was connected to a Ti-base abutment (Z 3.5 MIS Implant Technologies). The notch in the buccal side of the samples matched the concavity in the Ti base. Specific landmarks were traced with an indelible pen on the axial surfaces of the 3 aspects of each sample using SEM imaging JSM-IT100 to standardize the SEM analysis at completion (Figure 4). Figure 3: The AMD (absolute marginal discrepancy). The 25 samples were not sectioned and scanned with SEM imaging (JSM-IT100). For image mapping, the secondary electron imaging mode (SE) for scanning was used in this study. The operating conditions in this study were: beam energy 5 kV, working distance 15-20 mm, height 15 mm, and magnification \(\times\)500. SE was used to produce a topographic SEM image from the surface. SE images have a high resolution that are independent of the material and are acquired from inelastically scattered electrons close to the surface. The MD and the AMD were measured in 3 aspects of each sample under \(\times\)500 magnification (Figures 5-7). This high magnifying power was chosen since it provides a high degree of resolution that leads to precise measurements of the MD values between the parts. The MD average was obtained by measuring 10 points of each aspect per sample that represented the marginal misfit. The 10 measurements were calculated to one single value representing the MD. The AMD value was measured according to the cosine formula by using a ruler for evaluating the angle and MD value at the edge of each aspect per sample. The average of AMD was also calculated according to the cosine formula by combining the angle that was already measured for each AMD and the MD average obtained from each aspect. The average MD was obtained with 10 SEM measurements of each aspect. The average AMD was measured by combining the extension error and the average MD. Figure 4: The three blue dots represent landmarks of the three aspects that were scanned for each sample before and after cementation to provide consistent results. Figure 5: Steps in preparing the models and samples. Ti base  
The 25 substructures were cemented using self-curing luting composite (Multilink hybrid abutment cement, Ivoclar) according to the cementation protocol (Figure 8). The parts were pressed tightly together using finger pressure [4].