## 2 Virtual Reality in Periodontology (Gum Diseases)  
To understand the practicality for the utilization of a virtual reality simulator, it is essential to seek the foundations of diagnosing periodontal disease. Periodontal disease as newly classified as, _\"a chronic multifactorial inflammatory disease associated with dysbiotic plaque biofilms and characterized by progressive destruction of the tooth-supporting apparatus\"_[22]. The initial characteristics include loss of periodontal tissue support and bone loss, which may be assessed radiographically by the appearance of periodontal pocketing along with gingival bleeding. Other features include the presence of plaque/calculus and gingival inflammation. The biomarkers of periodontal probing pocket depth (PPD) and percentage bleeding on probing (BoP) are important parameters in classifying the disease and are dependent on the skills of a dentist. The measurement of these parameters involves the use of a periodontal probes [23]. These instruments require careful probing of the gingival sulcus around six areas per tooth with a standard pressure of 0.25 Newton (N) to chart the pockets. The probing pressure required to measure peri-implant disease is further reduced to 0.15 N [24]. Thus, motor skills and tactile perception of the gingival sulcus by the dentist are paramount in  
Figure 4: Classification of simulators based on their application in dental departments. aiding diagnosis of diseases. Furthermore, the removal of plaque/calculus by mechanical or ultra-sonic means also involves operator variability. The removal of calculus during non-surgical periodontal therapy also requires the operator to be alert with his perceptions of sub-gingival plaque or calculus. Traditional interventions allowed for the utilization of models or animal heads for the development of periodontal skills such as tissue handling and flap surgeries. However, in the modern era, various studies have reported success in using a virtual reality-based computer system. In Table 2, a detailed description of the reported studies is mentioned. A haptic virtual reality simulator system (PerioSim(r)) was introduced by [PERSON] et al. in 2007, the idea of which was taken from another audio-visual reality simulator called DentiSim [25]. PerioSim(r) introduced the haptic \"touch to feel\" sensation by having a stylus to interact with a physical dental model which is then portrayed visually in 3D. The result of the study indicated that it increased the students' tactile ability (although the representation of gingiva could not be registered into the system and some limitations were observed). Similarly, [PERSON] et al. introduced a haptic feedback system which registered pressure and pathway demonstrations [26]. Although it improved the tactile perceptions of its users, the accurate reconstruction of gingiva could not be registered into the system. Furthermore, [PERSON] et al. also proposed a haptic feedback virtual reality system which was specifically designed for periodontology [27]. It involved the simulation of probing skills and caries removal. The results obtained from his study indicated remarkable improvement in students' perception and tactile ability to replicate performances, but the system could not fully replicate the environment of a clinical setting or cutting instrument. The major advantage which was seen as being common in all the aforementioned studies was the improved tactile perception and ability of a student to detect and appreciate the anatomical considerations. Another advantage was that these virtual reality systems were less time consuming than conventional training classes. Considering that drawbacks in delivering pristine education can sometimes occur due to tight schedules and lower strength of professional faculty available, these systems can prove to be useful as they do not require more training staff and are self-explanatory in their use. Despite all the benefits of this technology, the major drawback is the cost-effectiveness of the devices.