## 4 Discussion
For internal adaptation, while some studies have indicated that an ideal range is between 70 and 120 um [24], there are also studies that suggest values between 50 and 100 um could result in the most favorable resin cement performance [25; 26]. In this study, the internal gap values (CBCT group: 224.64 \(\pm\) 49.98 um; intraoral scanner group: 124.55 \(\pm\) 26.51 um; model scanner group: 153.73 \(\pm\) 19.02 um) are above the clinically ideal gap values for all groups. Notably, axial internal gap (AIG) measurements showed higher values than occlusal internal gap (OIG) values. Therefore, it is suggested that the more retentive axial regions could affect the internal fit. Studies investigating the effect of cavity preparation on fit have similarly shown that non-retentive preparations have better adaptation [12; 27]. CBCT is used in many areas of dentistry, but its application in tooth-supported restorations is relatively recent and more limited. [PERSON] et al. [7] evaluated the marginal fit of crown restorations fabricated from CBCT data. They reported that restorations produced from images obtained at three different voxel sizes (0.125 mm, 0.20 mm, and 0.30 mm) exhibited clinically acceptable marginal gap values. Similarly, [PERSON] et al. [2] highlighted that interim crowns produced from CBCT data were within clinically acceptable marginal gap ranges. [PERSON] et al. [1] also stated that monolithic zirconia crowns produced with CBCT data exhibited marginal gap values below 120 um. The fabrication of restorations with CBCT data in the literature is limited to crowns, and no articles have been found regarding its use in inlay restorations. In this study, however, both the marginal and internal fits of inlay restorations fabricated with data obtained from CBCT scans (0.075 mm) were evaluated. For inlay restorations, CBCT did not show as successful gap values as intraoral and model scanners; the marginal gap range of inlay restorations produced from CBCT was found to be above the acceptable limits. [PERSON] et al. [9] reported that intracoronal restorations showed less trueness and precision compared to extracoronal restorations. Similarly, [PERSON] et al. [28] in their study examining the effect of restoration type on marginal fit, emphasized that crown restorations tend to have less marginal gap compared to inlay and onlay restorations [28]. The high marginal and internal gap values of CBCT, which have shown successful results in crown studies, in this study could be attributed to the complex geometry of inlays, which are a type of intracoronal restoration. The voxel size also affects accuracy by influencing the spatial resolution of orthogonal slices: the smaller the voxel size, the better the accuracy [29]. [PERSON] et al. stated that voxel size had a significant effect on the marginal integrity of CAD/CAM-fabricated crowns on virtual three-dimensional tooth models derived from CBCT imagings [7]. In this study, considering the positive effect of smaller voxel size on accuracy, a voxel size of 0.075 mm, which has not been used in previous studies for crowns or inlays restorations, was chosen. The capability of the software program to convert DICOM data obtained from CBCT into STL format may also have influenced the marginal and internal fit of the inlay restorations [2]. [PERSON] et al. [30] stated that the accuracy of segmentation is the primary factor affecting the precision of models. In this study, Planmeca Romexis version 6.2 was used as the conversion software. The program is the native software of the CBCT device and has very high precision. One of the key limitations of this study is the lack of direct validation of the STL files generated from CBCT DICOM data using a known gold standard, such as micro-CT-derived STL models.