# Estimation of Distances in 3D by Orthodontists Using Digital Models
### VR in Orthopedic Dentofacial Orthodontics  
The use of VR has also seen developments in the fields of orthopedic dento-facial orthodontics and orthognathic surgery. It played a major role in the initial and continuing training of practitioners. Indeed, the 3D acquisition of the different tissues of the head and neck provides a realistic platform for training in facial and dento-facial orthopedics [9]. For example, a new approach to virtual reality has been introduced and validated for cephalometric assessment by lateral view teleradiology [10]. A series of case studies using haptically activated computer-assisted cephalometry was performed. The authors showed that by providing tactile sensory feedback, errors in the cephalometric analysis were reduced, and tracking became more feasible and more intuitive. Another example is the use of the Voxel-Man simulator [11] in virtual apicoectomy, which revealed that, out of 53 medical dentistry students who performed a virtual apicoectomy, 51 had a positive evaluation of the impact of the simulation virtual as an additional modality in dental education. Among clinical applications, techniques have been developed to obtain data on the soft and hard tissues of the maxillofacial area in order to produce virtual 3D models for analysis and surgical planning [12]. These techniques have overcome the disadvantages of 2D photographs and X-rays. Four main types of 3D imaging systems have been used to capture dental and orofacial structures, in particular conical beam tomography or CBCT, laser scanners, structured light scanners, and stereophotogrammetry [13]. Among these applications, one of the most important, in terms of impact and development, is computer-assisted 3D modeling of dental arches. Indeed, dental arch models are very useful for orthodontists [14]. They are an essential part of diagnostic information and are used to document the original condition, to design and measure the effect of treatment. They reduce the difficulty of 3D visualization of dental axes and positions during the clinical examination. Dental arch models have a central role in orthodontic practices around the world. Until recently, plaster casts obtained from an imprint of the dental arches (Figure 1) were the only means to generate three-dimensional models to accurately represent the dental arches and malocclusions. 3D digital models have recently become a dematerialized alternative [15]. These models are electronic recordings of teeth and of the occlusion of a patient obtained with an intra-oral optical camera (Figure 1). The optical imprint of the dental arches is treated by software that draws a 3D projection, obtained from stereo-lithography (STL) files, on the computer screen. The features of the software allow the observer to change the view and to pivot or incline the image of the model. The software also allows measurement and storage of the circumferences of the arch, the diameter of the teeth, etc. Digital models have the advantage of electronic storage and remote access from multiple locations, thereby reducing the risk of loss or damage to the models. This VR technology can be considered to be part of VR as it represents two of its key characteristics:  
* Manipulate the imprints virtually on the screen. There is, therefore, a real-time interaction, which allows the user to modify the properties of the environment with which he interacts [11; 16]. * Deploy, thanks to the practitioner's diagnosis and therapeutic projection, a cognitive activity in space created digitally by 3D models (which is another key element of VR) [2]. In these 3D models, the virtual environment is not immersive because the models are viewed on a computer screen. However, there are applications that allow you to create an immersive environment using a head-mounted virtual reality screen to view models [17]. Interaction with digital work models is performed using a mouse, most often a 2D mouse, although it is also possible to use a 3D mouse.