## 1 Introduction
### Virtual and Augmented Reality: Two Mainstays in the ICT Era  
Extended Reality (XR) is the umbrella category that encompasses all the various forms of computer-altered reality, including Augmented Reality (AR), Mixed Reality (MR) and Virtual Reality (VR), which are Information and Communication Technologies (ICT) part of the emerging technological evolution and already widely used in the entertainment and military industries.  
VR involves the use of immersive computer simulation methods, e.g., 360\({}^{\circ}\) videos, 3D modelled videos, by the usage of a headset with headphones, a screen and a gyroscope. More affordable technologies (such as cardboards: foldable paper viewers) have been introduced in the market in past few years, promoting an increased diffusion of VR technology in everyday life. While the facilitated access to VR technology has led many costumers to develop experiences with no need for coding, the development of complex VR experiences, which include interactions with the virtual environment by joypads or other human interface devices, still requires dedicated ICT teams.  
AR can be defined as an enrichment of the perception of the real world by adding new layers of information that otherwise would not be possible to be perceived by the user. This ICT requires the usage of headsets that could be transparent or include cameras to stream the real-time video on an inside screen where the new layers are added. AR is quite expensive in comparison to VR and requires dedicated teams to create even simple AR experiences, in which the roles of the ICT developers and computer graphics are crucial. Even if AR could be considered an enhanced tool, the limits linked to the resources needed make them difficult to be developed in a broad spectrum of applications. Recently, the increasing physical elaboration capacity of the consumer-technology has piloted the development of applications that use the screen, the camera and the gyroscope of mobile devices to propose AR experiences.  
Further developmental progress has made VR integrated with AR, creating a new blended experience known as Mixed Reality (MR). The MR term usually refers to artificial products that could interact with the users in the real world. It has been introduced in different health educational scenarios, such as physiology or anatomy, in which the 3D representations of a model can help students better understand morphology and the relations of rendered objects.  
Thanks to the increase in consumer-level devices with XR capabilities, the current literature has focused on the role of the XR technologies to boost the educational patterns in different health scenarios, such as surgery [12], dentistry [13], health professions students' education [14], and patients' education [15]. Furthermore, a recent systematic review on the use of XR experiences in education reported how most of the studies available in the current literature have shown at least non-inferior results in terms of learning when compared to conventional teaching and training, while enhancing the enthusiasm and enjoyment [16]. The engagement to which XR technology leads could make this technology a useful companion to conventional education, while its growing availability could represent an opportunity for lower- and middle-income countries to gain access to more specialised training.