Implant placement aims to restore acceptable esthetic and function without affecting the surrounding soft and hard tissues. Rocharles C et al.  stated that high-density structures with great atomic numbers, such as dental implants, induce the beam hardening phenomenon in CBCT scans, affecting image quality and diagnosis. High-density materials act as filters that attenuate lower energy photons, leading to only higher energy photons left to contribute to the beam. Hence, the mean beam energy increases, resulting in data reconstruction error. This error leads to a deterioration in the image quality adjacent to these objects, demonstrated as linear structures, bands, or shadows. In addition to beam hardening, scattering also affects the image quality causing views such as cups, streaks, and dark bands between dense objects or at sharp edges. Due to the beam hardening and scattering, artifacts appear nearby high-density objects such as dental implants and thus severely reduce the diagnostic value of the images .
Studying the amount of artifacts induced by different implants helps decide the type of implant in clinical applications and can benefit the complication diagnosis and patient follow-up . However, Chagas M et al.  found no significant difference regarding diagnostic accuracy between CBCT images of peri-implant bone defects around titanium implants and zirconium dioxide implants.
Numerous literature has studied the effect of various parameters, such as FOV, kVp, mA, system type, exposure time, type of material, and surrounding bone, on artifacts by the dental implant in the CBCT images [3, 26, 27]. Though, how we should change the exposure parameters depending on the specific CBCT system or type of implant being used is still a controversial matter. Hence, this study was conducted to investigate the effect of different exposure parameters and implant materials on the amount of artifacts based on the CBCT system and exposure settings used routinely in our office. Exposure parameters, including FOV and resolution, were studied in the Cranex 3D CBCT system.
Our results showed that the amount of artifacts around zirconium implants was higher than in titanium implants. This outcome confirmed the effect of implant material on the image quality. According to the Mendeleev table, titanium atoms have an atomic number of 22 and a density of 4.506 g.cm− 3, and zirconium atoms have an atomic number of 40 and a density of 6.511 g.cm−³. This difference in atomic numbers and densities of the two implants materials may justify the higher amount of artifacts in zirconium implants.
Shokri A et al.  examined the effect of different exposure settings in a CBCT system on reducing the metal artifact around dental implants at different bone densities. The results showed that implants induce different amounts of artifacts in CBCT images by altering conditions such as FOV, bone density, time, amperage, and voltage. Notably, the effect of voltage on the amount of artifacts was more than other factors. Therefore, in order to equalize the conditions and eliminate the mediating factors, we set the same setting (90 kVp and 10 mA) and bone density in all images and conducted the study in two FOVs (4×6 cm2 and 6×8 cm2) as well as two resolutions (high and low) .
Sancho-Puchades M et al.  compared the artifacts generated by titanium, titanium-zirconium, and zirconium implants in vitro. They inserted implants in 20 bone models of human mandibles and investigated the amount of artifacts in CBCT images (KaVo Dental GmbH, Biberach, Germany). Similar to our observations, they concluded that the amount of artifacts produced by zirconium implants was more considerable than others. It should be mentioned that they used different exposure settings of 120 kVp, 5 mA, and 26 s radiation time.
Fontenele RC et al.  also investigated the amount of artifacts induced by implants inserted in the human mandible at distances of 1.5 cm, 2.5 cm, and 3.5 cm with angles of 65°, 90°, 115°, and 140° by three various CBCT systems (Picasso Trio, ProMax 3D, and 3D Accuitomo 80). Using 80 kVp and 5 mA exposure settings, they concluded that zirconium implants produce the most significant artifacts. This outcome was in line with our study. Observations showed that titanium implants created the same amount of artifacts regardless of the CBCT system type used for imaging, while zirconium implants showed different amounts of artifacts depending on the CBCT system.
In 2017, Smeets R et al.  examined artifacts caused by zirconium, titanium, and titanium-zirconium implants in magnetic resonance imaging (MRI), conventional tomography (CT), and CBCT images using almost identical exposure conditions as ours (90 kVp, 8 mA, 13.6 s). In MRI images, the amount of artifacts from the zirconium implants was the least, while in the CT and CBCT images, the titanium implants had produced the minimum amount of artifacts. As a result, they suggested MRI as the excellent choice of imaging for patients with zirconium implants and CT or CBCT for patients with titanium and titanium-zirconium implants. It is mentionable that the advantage of this study was to explore the amount of artifacts in different imaging modalities; nevertheless, it confirmed the results of the present study.
In addition to the implant's material, the present study showed that FOV is one of the factors influencing image quality. FOV size varies based on the system used for imaging, and it should be carefully set so that the resulting image can provide valuable information for the patient's diagnosis and treatment plan. Selecting the appropriate FOV size reduces the patient radiation exposure and enhances the image quality . As the radiation field enlarges, the pixel size rises, which increases the fill factor and the radiation-sensitive surface, thus reducing the amount of noise. Expansion of the radiation field results in more beam scattering, which increases the amount of artifacts and noises. However, the pixel size has a more definite effect on image quality, diminishing the beam scattering influence .
In the present study, the amount of artifacts around the implants decreased by the FOV expansion. Previous studies have also found FOV as one of the main factors affecting image quality. In agreement with our results, Pauwels R et al.  suggested that the large FOV performed better than the small one using the 3D Accuitomo 170 system (90 kVp, 5 mA) for imaging.
Shokri A et al.  studied the effect of FOV size on gray values in CBCT images. They implanted 4 acrylic cylinders in acrylic phantoms, each containing various materials used in maxillary grafts, including Nanobone, Cenobone, Cerabone, and water (as a control group). CBCT images were taken using 90 kVp, 5 mA, and two different FOVs (4×6 cm2 and 6×8 cm2). The results showed that FOV significantly affects the quality of images. The smaller FOV resulted in more variability in gray values and thus increased amounts of artifacts, which was consistent with the current study.
Whether an increase in FOV reduces or increases the amount of artifacts depends on many factors such as the CBCT system, exposure conditions (voltage and amperage), test performance, the bone or material used for implant insertion, the amount of beam scattering, and the amount of generated noise during the FOV changes.
In 2013, Parsa A et al.  examined the CBCT parameters (FOV, spatial resolution, number of projections, exposure time, and dose selection) on the gray value measurement in the implant area. This study included two CBCT systems (Accuitomo 170 and NewTom 5G) and Multislice CT (MSCT) for imaging. In both CBCT systems, selective spatial resolution and FOV significantly affected gray value measurements. The results presented more significant artifacts with FOV increment by Accuitomo 170 (90 kVp and 5 mA), which was not in line with the present study. This conflict might have resulted from image reconstruction and post-processing differences between the two studies. However, the results obtained from the NewTom 5G (110 kVp and 0.57 mA) showed that the amount of artifacts decreased with FOV increment, which is consistent with our study.
Regarding the effects of resolution alterations on imaging quality, we observed more artifacts with high resolutions in both study groups, but the results were only statistically significant for the zirconium implants group. Therefore, reducing the resolution seems to benefit the quality improvement of CBCT images from zirconium implants.
Resolution is the ability to detect small details on images, and it depends on the voxel size of the digital systems. According to Shokri A et al. , smaller voxel sizes can increase the resolution. Voxel size is a critical factor that affects the quality and duration of CBCT images reconstruction . Theoretically, as the voxel size decreases, the detector's radiation-sensitive surface decreases, resulting in higher noise levels in the images. Consequently, there is a need to increase voltage, amperage, or radiation time to improve image accuracy. Thus, reducing the voxel size increases the image's resolution at the cost of additional image noise and patient exposure .
A study by Parsa A et al.  showed that higher resolutions lead to higher amounts of artifacts. This inconsistent result with ours might be due to the differences in the systems' spatial resolution used for imaging.
In conclusion, the amount of artifacts induced by dental implants is an inevitable factor affecting the quality of CBCT images. Although, it could be diminished by enhanced precision in interpreting images, improved accuracy in choosing the type of implant, and more attention to imaging settings such as FOV and resolution. Within the limitations of this study, using CBCT Cranex 3D with exposure settings of 90 kVp, 10 mA, and 6.1 s, increasing the FOV and decreasing the resolution minimize the artifacts. Furthermore, zirconium implants induce higher amounts of artifacts than titanium ones.