# Abstract
## 1 Introduction
the Simodont (Nissin Dental Products Inc., Kyoto, Japan) [29; 30] and the Unidental MR simulator [31] have been reported to improve important indicators in the preprosthetic treatment of prosthetic dentistry. These simulators are capable of simulating abutment tooth formation. However, wearable displays, such as HMDs, present many challenges in terms of long-term use and hygiene: HMDs are wearable devices and can provide accurate stereoscopic viewing, but the interpupillary distance must be adjusted for each wearer and then reflected in the device. It has also been reported that there are side effects, such as headaches, dizziness, and blurred vision, in VR environments that can occur when using HMDs [32; 33; 34], making it essential to minimize so-called VR sickness as much as possible. Two-dimensional displays and HMDs have drawbacks, struggling to grasp depth perception properly, and they diverge from the actual visual environment of abutment tooth formation. In many dental practice VR simulators, teeth occupy only a small percentage of the screen, and visual recognition via the limited field of view of the HMD differs from the clinical dental treatment environment [35]. In particular, there is a discrepancy in the perception of distance sensations at close ranges [36; 37; 38]. Distance perception is very important in dental practice, especially in dentistry, which requires an accuracy of 0.1 mm at distances within 1 m. VR simulators with HMDs struggle to reproduce distance accurately and faithfully. To address these limitations, [PERSON] et al. [39] constructed a VR environment using a spatial reality display (SRD) capable of stereoscopic viewing without an HMD (Figure 2c). Measuring root canal length is crucial for endodontic treatment and it is often measured visually, using cone beam computed tomography (CBCT) in clinical practice. Traditionally, root canal length is measured using images that are sliced on a 3D axis through 3D medical image decomposition software or via 3D-CG models on conventional 2D displays. However, SRD-based software has demonstrated both high accuracy and speed [40]. One of the most important items of SRD research in dental education, namely, its use in dental practice training, has not yet been studied. The purpose of this study was to verify whether abutment formation on the SRD--which is a 3D-CG dental model that can be viewed stereoscopically with the naked eye at close range--would improve the cost-effectiveness of abutment formation practice and provide sufficient learning. This was performed by reading the digital data of dental models, obtained with an intraoral scanner, used in conventional training. This study aims to verify whether performing abutment formation on the SRD, which enables 3D-CG tooth models meant to be viewed stereoscopically with the naked eye, improves the cost-effectiveness of abutment formation practice and provides sufficient learning effects. For verification, a new abutment tooth formation simulator application using SRD was developed this time. By using this application, the accuracy of the perception of stereoscopic content without an HMD was verified. Specifically, a new abutment tooth formation simulator using a 2D display was also developed, and quantitative evaluations were conducted to compare the differences between the procedure using the naked-eye stereoscopic SRD-based abutment tooth formation simulator and the simulator with a 2D display. Through these evaluations, we analyzed the learning effect and usefulness of the 3D-CG dental teeth model on the naked eye's stereoscopic display in abutment tooth formation and automatic evaluation. Research issues include the accurate reproduction of a sense of distance that approximates clinical practice in training for abutment tooth formation using VR and the possibility of training with non-wearable devices.