## 1 Introduction  
Several efforts have been made to use virtual reality (VR) and augmented reality (AR) for medical and dental education and surgical support. In addition, these technologies have been shown to be helpful during use in several VR- and AR-assisted surgeries [1, 2, 3, 4], and beneficial in several reports of anatomy education using VR and AR [5, 6, 7, 8, 9]. The current methods still require wearing devices, such as a head-mounted display (HMD) and smart glasses, which pose challenges in hygiene management and long-term use. Several reports have also reported eye fatigue and sickness when using HMD and AR smart glasses [10; 11; 12; 13; 14; 15; 16; 17; 18].  
Additionally, it is necessary to measure the user's interpupillary distance (IPD) and to reflect it in the device settings each time to display 3D images accurately. Measuring the user's IPD takes 2-3 min each time, which makes the device unsuitable for daily use in a busy medical field, or an educational field in which dozens of students use it for a short time. Microsoft HoloLens, a common type of AR smart glasses, has a specification that requires the 3D-CG model to be placed at least 1 m from the eye to be seen in true 3D [19]. In other words, 3D-CG models located as close as 30 cm in proximity do not appear truly three-dimensional. This is a structural problem of AR smart glasses that requires a solution. It is necessary to display 3D-CG models with perfect stereoscopic effects within a close range of 30 to 50 cm for surgery and anatomy education. In the past, 3D displays that can be viewed stereoscopically with the naked eye have been researched and developed. However, these displays are not practical, as it is challenging to achieve both a high-quality image and high-speed screen refresh rates [20; 21].  
This study developed and implemented a novel anatomy education method using a spatial reality display (Sony, ELF-SR1, Tokyo, Japan, 2020) capable of stereoscopic viewing with the naked eye without an HMD or smart glasses [22]. The spatial reality display (SRD) can display a 3D-CG model with perfect three-dimensionality within a close range of 30 to 50 cm. The SRD can display 3D-CG models at 4K resolution and offers high-speed screen refresh rates, making it practical. Although 3D displays that do not require 3D glasses exist, they have low resolutions and cannot present highly accurate 3D images due to a phenomenon called \"crosstalk\", in which the image displayed to one eye is mixed with the image displayed to the other eye [20; 21]. An SRD overcomes these problems of conventional 3D displays and is the first truly practical product available for purchase on the general market. Its price is approximately USD 5000, and it requires a PC with a value of about USD 2000 to run the application. Currently, there are no commercially available applications for SRD, so users must develop their own. There are also no applications for medical and dental education. This study developed and evaluated the usefulness of two new applications for a spatial reality display: (1) a head and neck anatomy education application called SR Anatomy, which can display 3D-CG models of the skeleton and blood vessels of the head and neck region using 3D human body data available free of charge from public research institutes, and (2) a DICOM image autostereoscopic 3D viewer called DSR View, which can automatically convert 2D CT/MRI/CBCT image data into 3D-CG models.  
In total, 104 students at the School of Dentistry experienced and evaluated SR Anatomy. In addition, 12 dentists working at the University Hospital experienced DSR View and commented on its use. To evaluate the accuracy of DSR View, we compared the interdental distance of the actual dental education model and the distance of the 3D-CG naked-eye stereoscopic display of the DICOM data obtained by CT imaging from the actual model. We analyze the results of these assessments and discuss their usefulness as a new anatomy education method.