## 4 Discussion
On the other hand, conventional radiographs are two-dimensional and may present a distorted view of the imaged structures [32]. Our findings suggest that while CBCT is more beneficial for the diagnosis of strip perforation, for the detection of separated endodontic instruments, obtaining another periapical radiograph with a different horizontal angulation might be preferable to CBCT scanning. In the joint position statement developed by the American Association of Endodontists and American Academy of Oral and Maxillofacial Radiology, CBCT with limited field of view was recommended as the modality of choice for treatment complications such as separated endodontic instruments [33]. However, in our in vitro study, digital periapical radiography was superior to CBCT for the detection of separated rotary files. Similar findings were also observed in the other studies discussed above. One reason for the difficulty in the correct detection of endodontic instruments in CBCT images is the presence of artifacts. Artifacts are defined as systematic discrepancy between CBCT gray values and actual attenuation coefficients [34]. Artifacts occur as a result of several etiologic factors. For instance, area detectors in CBCT detect scatter radiation from the entire imaging field. Moreover, high-density materials create additional artifacts by hardening X-ray beams [35]. Gutta percha, endodontic instruments, and root canal sealers are materials with high density which may participate in the production of beam-hardening artifacts [36; 37; 38]. Scanning parameters such as exposure settings, voxel size, CBCT device, and field of view alter the magnitude of these artifacts [35; 39]. Blooming is another imaging artifact which may lead to overestimation of the object size in CBCT images. This artifact is a result of several factors, such as beam hardening and low spatial resolution [40]. For instance, implants placed in the jaw bones of frozen human cadaver heads showed an average blooming of 12-15% in their size [41]. Blooming can alter the shape and size of the separated instruments in CBCT images, making detection more challenging. These artifacts are not present in the periapical radiography, and thus they do not compromise the accuracy of detecting separated instruments in periapical radiographs. In addition, the low contrast resolution of CBCT, which is a result of area detectors collecting scattered radiation, can compromise differentiating file fragments from gutta percha material in the filled root canals [17]. The three-dimensional nature of CBCT imaging, however, helps in the detection of several endodontic complications. For instance, as our findings show, the strip perforation of root canals can be better detected using different CBCT image views. Axial views can show the extrusion of endodontic filling materials from the danger zone of roots. This view cannot be obtained by periapical radiography. In addition, using cross-sectional views in different planes, the root canal can be viewed with smaller thicknesses, whereas periapical radiography as a conventional imaging technique provides the ray-sum of the entire thickness of tooth, supporting bone, and soft tissues. One of the limitations of this study is its in vitro design, which relies on the simulation of clinical scenarios that may not be accurate. In addition, the poor interobserver agreement observed in the detection of separated files in CBCT images reflects the low diagnostic potential of CBCT images for detecting file fragments. It is worth noting that this study used specific types of endodontic instruments (i.e., ProTaper F2 rotary files) for the simulation of instrument separation. The results may vary for instruments with different sizes or materials. Additionally, strip perforations were made in the coronal third of the canal. Simulating perforations in different regions of the root canal may lead to different findings.