## 4 Discussion  
For the purpose of this study, the fitness and trueness of the 3-unit FDP fabricated by two digital workflows and their correlation were evaluated. The first null hypothesis (the 3-unit FDP fabricated by the two digital workflows was not different in the assessment of fitness and trueness) was rejected (\(p<0.001\)), while the second null hypothesis (which has no correlation with fitness and trueness) was partially rejected. Based on our findings, it can be seen that the difference in the equipment used in the digital workflow affects the fitness and trueness of the 3-unit FDP. In the same way, previous studies were carried out with different digital workflows according to the equipment used, and there were significant differences according to the workflow [2; 11]. In [PERSON]'s study [26], the digital workflow (\(222.5\pm 124.6\)\(\upmu\)m) showed a significantly higher marginal fit than the conventional workflow (\(118\pm 49.7\)\(\upmu\)m). The results were similar to the marginal fit (\(210.8\pm 83\)\(\upmu\)m) of the chairside (closed type) group presented in this study. [PERSON] [27] also reported a higher marginal fit with the digital workflow (\(86.17\pm 27.61\)\(\upmu\)m) than the conventional workflow (\(77.26\pm 29.23\)\(\upmu\)m). [PERSON] [28] also reported a higher marginal fit with the digital workflow (\(120.4\pm 54.5\)\(\upmu\)m) than the conventional workflow (\(75.4\pm 16.6\)\(\upmu\)m). However, in [PERSON]'s study [29], the marginal fit was significantly higher in the conventional workflow (\(11.56\pm 8.74\)\(\upmu\)m) than in the digital workflow (\(1.85\pm 1.50\)\(\upmu\)m). Previous studies have shown different results. According to the systematic review of multiunit FDPs fabricated using digital workflow [25], single FDPs fabricated using the digital workflow have been generally studied, but multiunit FDPs have been insufficiently examined, and further studies are required for clinical reliability. In this study, the marginal and internal fit of the in-lab (open type) group were significantly lower at all measurement positions (\(p<0.001\)). The most significant steps for the fabrication of FDPs are the scan acquisition process and the CAM process [21]. Among them, the scan acquisition process can  
Figure 9: Relationships between the trueness of the milling unit and fitness. (**A**) In-lab group (trueness and marginal fit, \(p=0.070\)). (**B**) In-lab group (trueness and internal fit, \(p=0.013\)). (**C**) Chairside group (trueness and marginal fit, \(p=0.855\)). (**D**) Chairside group (trueness and internal fit, \(p=0.701\)). have the greatest influence on FDP fitness [30]. [PERSON] [2] evaluated the accuracy of casts produced using conventional and digital workflows and reported poor accuracy of the digital workflow using intraoral scanners. [PERSON] [1] reported that the scan error increases as the range of the intraoral scans increases, and the recommended scanning range from single to 3-unit FDP, according to the intraoral scanner. Thus, the limited scan range of the intraoral scanner is responsible for the poor fit of the 3-unit FDP. In our study, a fully digital workflow was designed using only one manufacturer's product (CEREC). Recently released equipment from different manufacturers can be used in each process [2]. Therefore, additional studies using a combination of recently introduced intraoral scanners, CAD software, and milling units from various manufacturers are needed. Trueness indicates the similarity between the CAD reference model and the CAD test model [21]. Previous studies have evaluated the trueness of the CAM process [21]. [PERSON] [31] reported excellent trueness when using the three mill burs rather than the two mill burs. [PERSON]'s study [32] showed excellent trueness using the five-axial milling unit compared to the four-axial milling unit. In this study, two mill burs were used in the four-axial milling unit for both the chairside (closed type) and in-lab (open type) groups, and our findings show that the milling unit influences the trueness.