## 1 Introduction  
The development of minimally invasive dentistry has made it possible to preserve natural teeth for many [1]. The number of teeth requiring primary or secondary endodontic treatment is growing. Secondary treatment is considered more difficult and is associated with a lower percentage of successful treatments and a higher number of complications. The development of new technologies, including new tools to improve diagnosis and root canals treatment, such as new generations of rotary files, surgical microscopes, computed tomography, and diode and neodymium-YAG-erbium lasers, enables dentists to reduce the failure rate [2]. Many factors influence the efficiency of both types of endodontic treatment (primary and secondary), including the most important one, namely, the precise imaging of the root canal system, tooth root, and surrounding tissues [3; 4; 5]. The commonly used technique in endodontic treatment is two-dimensional (2D) dental radiographs [6]. In turn, two-dimensional images of three-dimensional areas inevitably lead to the loss of information. More information about tooth anatomy is introduced by the application of cone beam computed tomography (CBCT) in three-dimensional (3D) endodontics [3; 7; 8; 9; 10; 11; 12]. As a consequence, performing CBCT can have a huge impact on decision-making during the diagnosis and planning of endodontic therapy, especially in complicated endodontic cases [13; 14]. Taking into account these reports, the European Societies of Endodontics supports the use of CBCT in endodontic treatment, as long as the ALARA (as low as reasonably achievable) principle is followed [15]. The failure of previous treatment procedures, which were caused by difficulties related to anatomical abnormalities or iatrogenic actions (perforation, broken file), influenced the decrease in the treatment efficiency [14]. Using a 3D hologram based on CBCT, the dentist can visualize the real anatomy of the tooth, including hidden curves, calcifications, perforations, or other structures, such as broken tools. Thanks to such detailed diagnostics and case analyses, it is possible to reduce iatrogenic errors during procedures using hand or rotary files. If the hidden curvatures of the root canal are not properly recognized, they lead to an increased load on the instrument and may lead to its fracture. Immersive technologies, including virtual reality (VR), augmented reality (AR), and mixed reality (MR), offer new possibilities for imaging root canals [16; 17; 18; 19; 20]. The application of VR for root canals was presented by [PERSON] et al. [21]. Eleven students used a virtual simulator, i.e., Dental Simulator v1.13 for iOS and Android in the Serbian language, for learning how to perform local anesthesia during the COVID-19 pandemic. Immersive technologies can also be applied to the planning of maxillofacial procedures and surgery training [22] or aesthetic dentistry [23]. An interesting case of the application of AR in dental care, namely, one patient with multiple missing teeth, diastemata, and impaired masticatory, as well as phonetic ability, was presented by [PERSON] et al. in [24]. It turned out that the use of AR improved communication between the dentist and the dental technician. In turn, the combination of CBCT and AR in the area of navigation of dental implant placement was shown by [PERSON] et al. [25]. First, the method was developed on a model and then verified experimentally on a single volunteer. In turn, [PERSON] et al. showed an accuracy of 85% in mandibular visualization with AR technologies [26]. It turns out that the use of immersion technology saves time with no loss in navigation accuracy. The mixed reality was also proposed to create anatomical structures intraoperatively in oral and maxillofacial surgery by [PERSON] et al. [27]. The method was validated experimentally for both a pig jaw and one patient operation, i.e., the case of a maxillary cyst next to the root of tooth 13. Moreover, AR technologies may also be helpful in anesthetic injection [28].