## 4 Discussion
Therefore, considering the patient's exposure, the use of a low tube voltage and iMAR was a very effective CT scanning method. However, since the purpose of this study was to reduce artifacts to the maximum extent feasible and output them using a 3D printer, data obtained under high voltage were used in this experiment. Data acquired under high voltage suggested a greater effect of normalization because of low HU values in the neighboring tissue in the prior image data from which the metal signal was deleted following iMAR application. When data were acquired at high tube voltage and iMAR, the artifacts were lower. In conclusion, the 3D-printed output was enhanced when data were acquired at high tube voltage and images were subjected to iMAR. Therefore, as shown in Figure 4b, the shape of the metal artifact remained unchanged in the images not subjected to iMAR, so it was not possible to present the shape of the tooth. However, in the case of Figure 4c, metal artifacts were eliminated partially, and the original phantom shape was reproduced. In this study, the signal value of the structure under the metal component was low, which was observed in the form of a defect in the 3D-printed output, presumably due to a geometric phenomenon during the CT scan of the phantom. In general, during CT, data are collected in a helical form on the same plane as the arrangement of dentition. In this study, data were collected in the vertical direction of the plane of dentition. As for metal artifacts, if there is a metal structure in the X-ray scanning direction during CT, low-energy X-rays are absorbed as the X-rays pass through the metal, resulting in an increase in average energy. Thus, in the presence of a metal structure in the direction of X-ray scan, the average energy in the scanning axial direction reduces the uniformity and affects the HU of the subject. Therefore, if the geometrical position of the metal is considered and the angle of the CT scan is determined, the occurrence of artifacts in the raw data can be adjusted. Further, it is expected that this data loss part would be sufficiently accurate if computer-aided design (CAD) using medical images or specific software is used. In this study, it was meaningful to evaluate the degree of metal artifact reduction according to the application of the iMAR technique and to confirm the possibility of 3D printing. We did not use 3D CAD using commercially available medical images, but reduced artifacts using the iMAR algorithm with free software and limited the evaluation of its utility in 3D printing tasks. Therefore, in this study, this entailed a direct application of basic knowledge regarding the theory of CT image acquisition and methods used to reduce artifacts that are generated. It was a study that could be directly applied in actual clinical practice. Therefore, it could be said that a method for setting conditions and reducing CT artifacts in patients implanted with metal prostheses and implants was proposed. This study has several limitations. As mentioned earlier, when 3D printing was performed using iMAR, the beam hardening artifacts could be reduced effectively. However, when software was used to design bone alignment and assistive technology devices based on recent medical images, a more elaborately calibrated printout was feasible. Second, the geometrical accuracy of the 3D printed product and the reference phantom could not be evaluated. For this purpose, a comparative measurement of marginal and internal fit with the reference phantom was needed. There were many factors that caused errors in the geometrical accuracy, but the performance of the 3D printer used was the main factor, suggesting the need for related studies.