CBCT has excellent help in diagnosing, treating and evaluating pulp diseases, but its image quality is often affected by many factors such as artifacts. Studies have shown that differences between the actual physical conditions of the measurement equipment and the simplified mathematical assumptions used for 3D reconstruction lead to artifacts[20]. Other factors, such as initial reconstruction, artifact reduction algorithm, projection polychromatic, patient movement, FOV and photon diffraction, all affect the generation of artifacts[2]. Clinical artifacts have a stripy appearance due to the substantial absorption of low-energy (lower wavelength) rays in the polychromatic spectrum emitted by X-ray sources as they pass through an object. For example, its internal absorption wavelength acts as a filter with a high density and high atomic number of metal materials.
Nanomaterials have unique structures and properties different from other materials and have been increasingly widely used in oral materials, among which nanoparticles are the most prominent[21] .For example, nanoparticles in clinical dental prosthesis composites can promote dentin remineralization and tubule occlusion [22, 23]. In addition, they can be used in combination with sealants, obturating material[24], intracanal medicament and irrigating solutions[25] for therapeutic use, providing new strategies for treating dental pulp diseases. Previous studies have confirmed that MCSNs have low cytotoxicity and strong antibacterial activity and can induce calcified tissue formation around the apical pore. Meanwhile, the high surface area and porous interior of MCSNs can serve as a reservoir for drug molecules. It can further destroy bacterial biofilm and prevent adhesion to dentin[19].
In this study, the artifacts of MCSNs in CBCT images were quantitatively compared with AH, iRoot SP and gutta-percha. The results show that the hypodense artifacts of MCSNs are not significantly different from those of other materials (P༞0.05), suggesting that MCSNs showed the same properties as existing materials in terms of hypodense artifacts, which met the requirements of radiopaque materials for root canal filling. However, When X-rays pass through, low-energy X-ray photons are absorbed, and the remaining high-energy photons are not easy to attenuate, leading to the beam hardening effect. After all, the generation of artifacts is related to the radiopacifiers and other chemicals in the formulations of these sealants, which may lead to different densities. The density of these materials can explain no significant difference between the hypodense artifacts of AH plus and iRoot SP in the experiment, which is different from the previous experimental results[15]. Clinically, hypodense artifacts may mimic diseases such as root fissures, or fractures in root fillings, negatively affecting diagnostic accuracy [8].
In addition, the study showed that the hyperdense artifact area of MCSNs was significantly lower than that of AH plus and iRoot SP (P < 0.01). While the radiation impermeability of bioceramic sealer is markedly lower than that of AH plus, which is consistent with previous studies [10, 15, 26]. Since this is the first time that artifacts produced by MCSNs have been evaluated, the atomic number of the nanoparticle materials is lower, considering that these filling materials have different atomic compositions. Compared with AH plus (oxygen Z = 8, silicon Z = 14, calcium Z = 20, iron Z = 26, zirconium Z = 40, tungsten Z = 74) and iRoot SP(hydrogen Z = 1, oxygen Z = 8, silicon Z = 14, calcium Z = 20, phosphorus Z = 15, zirconium Z = 40), MSCNs had the lowest atomic numbers (oxygen Z = 8, silicon Z = 14, calcium Z = 20)[27]. Studies have confirmed that hyperdense artifacts have a partial volume effect [28], which will blur the anatomical morphology of the root canal, hinder the detection of the region of interest, and seriously impair the evaluation of root filling teeth and the visualization of root canals, cracks and tooth fractures. These hyperdense artifacts may negatively affect the accuracy of diagnosis, especially in the clinical diagnosis of vertical root fractures (VRF) and perforation [29], which have a poor prognosis. Therefore, we tested the artifact expression of MCSNs and confirmed its obvious advantage in reducing the image density artifact area, which can effectively avoid misdiagnosis. We believe that MCSNs will become an attractive material in root canal therapy in the future.
There were no significant differences between the AH plus and the iRoot SP groups (P > 0.05). However, there were substantial differences in hyperdense and hypodense artifacts area between the MCSNs group and the GP group (P < 0.05), which were similar to previous studies [13, 30, 31]. Interestingly, the mean area and standard deviation results showed that MSCNs produced significantly fewer artifacts and were the root canal sealant material with the smallest artifact area.
Studies have shown that the different CBCT units [12, 32, 33] and exposure parameters (such as tube voltage, tube current, FOV and reconstructed voxel) lead to significant differences in the appearance of artifacts [14, 34, 35]. In this study, we used the same CBCT units and exposure parameters to eliminate the possible influence of these different structures on gray value and area assessment. In addition, although MCSNs are not yet clinically available, given the increasing use of CBCT in current dental practice, we believe that our results on the artifacts properties of this material will contribute to significant improvements in dental nanomaterials.