## 1 Introduction  
During periodontal diseases such as tooth decay, the shape of the tooth is acquired using a dental impression. The treatment entails the insertion of a dental implant. An irreversible hydrocolloid material, known as alginate, is used to obtain the dental impression conventionally [1, 2]. However, in this conventional method, since the alginate must be firmly maintained on the teeth, the patients may complain of discomfort during the acquisition method. The peculiar smell of alginate is not only repulsive to the patient but also affects the accuracy of the tooth shape during the patient's movement whilst taking the dental impression. In addition, areas in the tooth lacking firm bonding between alginate and the tooth during the extraction process can lead to errors in the tooth shape. Therefore, in order to overcome these limitations, and to alleviate patients' discomfort, digital data are being utilized to obtain impressions [3, 4]. A 3D scanner does not generate the unique odor of alginate, and thus avoids patient discomfort. The 3D scanner acquires the 3D surface data of the teeth and the model of the tooth and, based on the 3D printout, generates an implant appropriate for the patient's periodontal disease [5, 6]. The patient's information is processed digitally, obviating the need to store the patient's dental plaster model. The storage and management of the patient's dental information is easy and the optimal treatment method can be established via various simulations. The raw 3D data obtained with the scanner is converted into a stereophotography CAD software file (STL) and output to a 3D printer [7, 8]. However, the accuracy of 3D scanners with digital advantages is limited in the oral cavity and by changes in the scanner angle in the case of a patient with a small mouth or multiple structures in the oral cavity [9]. Recent advances in 3D printing technology using 3D medical imaging via computed tomography (CT) have been shown to overcome the disadvantages of 3D scanners and utilize the advantages of digital approaches [10; 11]. CT images can accurately express the morphological data of a mandible, including the tooth, and retain the advantages of digital data, such as simulations before and after treatment. CT images not only provide accurate coordinates, but also facilitate the acquisition of data via X-rays externally, eliminating the need for a separate instrument for obtaining a patient's oral impressions [12]. Notably, since surface data can be extracted by controlling the degree of absorption attenuation of human tissue, information associated with the density of teeth can be selectively post-processed. Accurate diagnoses of the internal condition, in addition to the surface information of the teeth, enables customized treatment based on the patient's condition. CT images contribute to scalability of the treatment; however, beam hardening artifacts due to metal can occur in the case of patients with metal implants in their teeth. In fact, 3D printing is impossible if there is a metal artifact in the CT image, with almost no practical clinical, use until now. As X-rays pass through the metal structure, beam hardening artifacts, which are generated in the form of flashes due to the changed X-ray spectrum, adversely affect the pathological diagnosis. Several efforts have been made to reduce the artifacts. Recent efforts have been made to increase image uniformity by applying an iterative metal reduction algorithm (iMAR) [13; 14; 15; 16]. However, taking impressions via 3D printing is not popular in the dental field to reduce such metal artifacts. The application of 3D printing by reducing metal artifacts has hardly been attempted in the dental field, until now. Therefore, the use of CT images in dental impressions could increase in the future if metal artifacts can be reduced. First, in this study, we identified the optimal conditions for reducing metal artifacts by acquiring CT data under various conditions and applying iMAR to minimize the metal artifacts in CT images.