## 4 Discussion  
This study compared the MD and AMD values of samples before and after cementation. The values of MD and AMD were significantly higher (\(p<0.05\)) after cementation compared with the values before cementation. Therefore, the null hypothesis of no difference was rejected. Previous studies have reported similar results. [PERSON] et al. concluded that the mean MD values of different types of crown systems cemented on Ti and zirconia implant abutments, which were measured using SEM, showed an increase ranging from 38.34 \(\upmu\)m to 46.58 \(\upmu\)m after cementation [18] Even using different types of cement did not change the outcomes. [PERSON] et al. used two groups of cements and ceramic crowns and reported that mean MD values were significantly lower before cementation (32.7 \(\pm\) 6.8 \(\upmu\)m and 33 \(\pm\) 6.7 \(\upmu\)m, respectively), compared to after cementation (44.6 \(\pm\)6.7 \(\upmu\)m and 46.6 \(\pm\) 7.7 \(\upmu\)m, respectively) [20]. Using a measuring microscope, [PERSON] et al. found higher MD values after cementation for three ceramic systems and two different cements. The mean MD value before cementation was 82.87 \(\pm\) 20.74 \(\upmu\)m, whereas it was 121.0 \(\pm\) 35.09 \(\upmu\)m after cementation [21]. [PERSON] et al. found that the MD of metal-ceramic and In-Ceramic implant-supported crowns before cementation were (52.65 \(\pm\) 11.83 \(\upmu\)m and 85.73 \(\pm\) 14.06 \(\upmu\)m, respectively), smaller than after cementation (66.80 \(\pm\) 15.86 and 89.36 \(\pm\) 22.66 \(\upmu\)m, respectively) [22]. Another study supported these results among teeth and implant crowns. The mean MD of all test groups before cementation was 45.7 \(\upmu\)m for teeth crowns and 15.17 \(\upmu\)m for implant crowns. A significant increase in the MD was found after cementation within the experimental tooth-implant-supported fixed dental prostheses (implants, 11.7-18.7 \(\upmu\)m and teeth, 13.4-24.2 \(\upmu\)m) [23]. Although there is no consensus among researchers regarding the definitions of marginal fit and measurement methods, several studies considered the MD values that [PERSON] and [PERSON] defined as the standard acceptable misfit [24]. They observed in their in vivo study of more than 1000 crowns that MD values less than 120 \(\upmu\)m between teeth preparation and crowns fabricated by conventional casting techniques were more likely to be successful. Most studies considered the prosthetic-abutment MD to be clinically acceptable around 100 \(\upmu\)m in casting techniques; although, some authors showed acceptable values ranging from 50 to 160 \(\upmu\)m [15]. However, the current study used CAD/CAM for fabrication and exhibited clinically acceptable MD values, with no MD measurement greater than 100 \(\upmu\)m reported for this system. According to a systematic review, the MD values of implant-supported prostheses using CAD/CAM showed MD values smaller than 110 \(\upmu\)m [11]. The few studies that examined AMD values were not related to implants but reported clinically acceptable values similar to those in the present study. An in vitro study evaluated the AMD of ceramic crowns fabricated using conventional and digital methods and measured the values using three-dimensional scanning. The AMD of the ceramic crowns fabricated using conventional methods and digital techniques were 115 \(\pm\) 15.2 \(\upmu\)m and 110 \(\pm\) 14.3 \(\upmu\)m, respectively [25]. Another in vitro study showed that the AMD value achieved for the four zirconia-based ceramic crown systems analyzed was within the range of clinical acceptance (120 \(\upmu\)m) [26]. The mean AMD values reported in the current study before and after cementation were smaller than 120 \(\upmu\)m. Since the AMD is the angular combination of the MD and the extension error, the MD values were smaller than the AMD values, as was expected [3]. Similar results were concluded by [PERSON] et al.