1 A Brief Survey of Visuo-Haptic Simulators for Dental Procedures Training Crenguta M. Bogdan 1, Alexandru F. Dinca 1, Dorin M. Popovici 1 Mathematics and Informatics, Ovidius University 124 Mamaia Blvd., Constanta, ROMANIA Abstract Recent advances in haptic technology and the wider availability of the haptic devices allow developers to construct visuo-haptic interfaces and simulators employed to simulate especially medical procedures. The visuo-haptic simulators combine visual and tactile information and provide training scenarios which help gaining or improving the trainee s skills. In this paper we review visuo-haptic simulators for dental skills training. We explore these systems focusing on the simulated dental procedure, the models of the real objects from both perspectives: visual and haptic, and the system evaluation. Regarding the evaluation we were interested in the methodology employed for evaluation, the number of evaluators considered in the process and its results. The results showed that the visuo-haptic simulators may help trainees to develop dental skills and most of the existent systems need to be improved in order to provide realistic simulations. Keywords: haptic feedback interface, visuo-haptic simulator, dental training Introduction Sense of touch has four submodalities: cutaneous, kinesthetic, proprioceptive, and pain. Cutaneous sense is stimulated upon contact with an object to feel the surface properties (like smoothness, slippage, and texture) and surface temperature of the object. Kinesthetic sense is stimulated by both hand and body movements and tensions. If the hand is moving on the surface of an object, we can identify shape, surface roughness, contact pressure, weight and inertia of the object. Proprioceptive sense refers to sensing the user s body position or posture. It is stimulated by receptors placed in muscles, tendons and joints. Proprioception provides spatial and motor information about object properties also interaction is strongly based on the forces experienced during touch action. Because of differences in the submodalities there are two types of interfaces in virtual reality applications: Interfaces with tactile feedback, which combine the cutaneous and kinesthetic senses. They are used in applications to explore the contact surface of a virtual object; Interfaces with force feedback, which combine the proprioceptive and kinesthetic senses. They are only used in applications where contact forces are given during the user interaction. These types of interfaces can be built independently or can be combined. When combined, they are called haptic feedback interfaces. The classic setup of a haptic feedback interface supposes the existence of 3D (stereoscopic) visual rendering (formed by stereoscopic display, polarized mirror and stereo glasses) together with a haptic interaction device (a metaphor of the real tool) (Figure 1).
2 56 University of Bucharest and "Babeş-Bolyai" University of Cluj-Napoca The user actions are expressed using the haptic interaction device which is part of the human interface devices category. This device is also a rendering one, since it is used to give a haptic feedback to the user as consequences of his/her actions. The user is also aware of the simulated environment s reactions through visual connection Visuo-Haptic Simulators In order to treat visuo-haptic simulators term we need to briefly review multimodal and visuohaptic systems. Multimodal system is a software system enhanced with multimodal capabilities for human/machine interaction and it is capable to interpret information gathered through different communication and sensorial ways. Visuo-haptic system is a multimodal system that provides the capabilities of (immersive) graphical rendering of objects, and computation and haptic rendering of virtual objects by the system as an answer to the user s actions. Forms of answer are: force, topological changes, etc. It can simultaneously receive input from the haptic interaction device, and output results as forces to the haptic interaction device or as 3D images to the stereo display. In some cases visuohaptic systems may also output sounds to the user (Figure 1). Visuo-haptic simulator is a visuo-haptic system that simulates the structure and the functions of a real operation or process, etc., used for training or testing. The system is responsible with the coherence between the simulated environment outputs and the user input. To this end, the challenge for a visuo-haptic simulator to be successful is, first of all, to synchronize visual collision and deformation with tactile feedback, each of these signals at a proper frequency. The collision between the virtual tool manipulated by the user through the haptic interaction device frequently produces local shape deformations on the virtual object geometry. These shape changes depend on object entropy and are counted in visuo-haptic simulator generated multimodal feedback. Here the simulator manages aspects such as friction, stiffness, viscosity and elasticity in order to compute the forces that have to be returned at haptic device level as reactions to the user actions. The role of simulators has been recognized as an important aspect of training in the health field that supports and improves the patient safety (The National Institutes of Medicine, 1999). In this paper, we provide a survey of visuo-haptic simulators for dental skills training. We explore these systems focusing on the dental procedure simulated, the real objects modelled from the both perspectives: visual and haptic, and the system evaluation. The paper is structured as follows. In Section 2 we provide a brief survey of dental visuohaptic simulators. Section 3 summarizes the results of the evaluation of some visuo-haptic systems. The paper ends with conclusions and bibliography. 2. Brief Survey of Visuo-Haptic Simulators for Dental Training Acquiring abilities and skills to perform dental procedures is essential for dental students. To date, these are gained in the laboratories of the dental medicine faculties in two stages. In the first one, dental students are trained on artificial teeth sometimes placed within a manikin head using real dental instruments, like burs, etc. The artificial models cannot provide the level of detail and material properties of real life teeth and procedures. In the second stage, the students perform dental procedures on real patients under the close supervision of their professors. So, the students go through a trial and error process achieving better and more consistent experience and safety performance of medical procedures. Haptic feedback interfaces have been introduced between the two instruction stages with better outcomes and less medical errors according to (Buchanan, 2001), (Leblanc et al, 2004) and (Jasinevicius et al, 2004). Instead of using real burs on patients, the trainee holds the haptic device
3 The 6 th International Conference on Virtual Learning ICVL stylus which has as virtual representation 3D models of real dental tools (burs, diamond tools, bevel instruments, etc.) and executes movements over virtual models of human teeth or mouth. Depending on the simulated dental procedure, the feedback of the employed simulator is represented by topological changes of the tooth structure or forces (sensations) in the hand of the trainee. The sensations are similar with those felt by the trainee when he/she executes the same dental procedure on a patient. Visuo-haptic feedback interface Real images of virtual tool and virtual object Visual (stereoscopic) display Semitransparent mirror Visual collision haptic interaction Virtual images of virtual tool and virtual object Visual and/or audio output 3D Input Haptic Real tactile sensation Visuo-haptic system Model virtual object virtual tool Figure 16. The link between a visuo-haptic interface and a visuo-haptic simulator
4 58 University of Bucharest and "Babeş-Bolyai" University of Cluj-Napoca 1.2. Dental Visuo-Haptic Simulators The followings are some of the most well-known haptic-based dental simulators developed until now. After a brief description, for each simulator we focused on the simulated dental procedure, the real objects modelled by the system and, in the next section, the results of the system evaluation. This activity has been carried out after training sessions performed by evaluators. One of the most important skills for any dentist is the ability to prepare and restore damaged tissue resulting from carious lesions. To date, this skill can be achieved by employing one of the next dental haptic simulators. Virtual Reality Dental Training System (VRDTS) has been developed by Novint Technologies and the Harvard School of Dental Medicine (Novint Technologies, 2011). It simulates the tissues which form the tooth structure (enamel, dentin, and pulp), the carries and the amalgam material that the trainee has to employ to fill a decayed tooth. The system also simulates dental instruments (explorer, drill, carrier, tamper and carver) enabling a trainee to practice cavity preparations. Iowa Dental Surgical Simulator (IDSS) has been developed by the College of Dentistry at the University of Iowa in collaboration with the Graphical Representation of Knowledge (GROK) Lab (Iowa Dental Surgical Simulator, 2011). The trainee employs a joystick and a modified handle from an explorer, a dental instrument with which he or she can explore tooth surfaces for carious lesions. During the exploration, he or she can feel healthy enamel, healthy dentin and carious dentin of a virtual tooth (Thomas et al, 2001). During the HapTEL (haptics in technology-enhanced learning) project (HapTEL, 2011) a visuo-haptic system has been developed in order to teach dental students how to operate the drill. The students feel the difference between drilling hard enamel and softer decayed tooth and gain experience in how much pressure is needed. The dental drilling simulation for the cavity preparation is also provided by the Virtual Dental Patient system (Marras et al, 2006). The trainee can perform drilling operation directly on the virtual model of tooth using either the mouse or the stylus of a Phantom Desktop haptic device. In the second case, the virtual representation of the stylus is the model of a dental bur. Holding the stylus, the trainee feels the contact/resistance forces which were calculated depending on the properties (stiffness, static and dynamic friction) of the objects. The removal of caries at various locations is also simulated by the VOXEL-MAN Dental (VOXEL-MAN Dental, 2011). In order to perform the dental procedure, the trainee employs the stylus of a haptic device to make cavities in the decayed teeth. The stylus has as virtual representation on the 3D display virtual models of burs of various shapes which are controlled by a foot pedal, as well as a dental mirror. Another study has proposed a visuo-haptic system that simulates probing and cavity preparation (Konukseven et al, 2010). To this end, the properties of enamel, dentin, pulp and carries were modelled and a trainee can feel the differences among these tissues. The system also renders 3D models of maxillary and mandibular dental arches and various dental instruments such as mouth mirror, probe and dental drills. The same process of drilling and removing of carious lesions is also simulated by the system introduced in (Kim et al, 2005). In order to increase the realism of the application, a drilling sound plays when the virtual drill collides with the virtual tooth. Simodont Dental Trainer simulates tasks for removal of tooth decay, filling cavities or crown and bridge preparation (Moog Inc., 2010). Achieving the skills needed to differentiate pathological and normal conditions, as well as to diagnose and treat periodontal diseases, can be realized by employing one of the two visuo-haptic systems: PerioSim (Steinberg et al, 2009) and a periodontal simulator. PerioSim has been developed at the University of Illinois at Chicago through the collaboration between the Colleges of Dentistry and Engineering (Steinberg et al, 2003). The application
5 The 6 th International Conference on Virtual Learning ICVL simulates clinical periodontal procedures, such as periodontal probing, the use of the periodontal explorer in the detection of subgingival calculus and a variety of other subgingival topographies (Steinberg et al, 2007). The periodontal simulator was designed and implemented by the Electronic Visualization Laboratory of the Department of Computer Science, the Industrial Virtual Reality Institute of the Department of Mechanical and Industrial Engineering, and the Department of Periodontics at the University of Illinois at Chicago (Luciano, 2006). The application simulates three dental instruments: a periodontal probe, a scaler and an explorer. With the first tool, the trainee measures the pocket depth and determines the tissue health and, in case of pathological situations, the severity of the periodontitis. The second one is used by the trainee to feel the virtual calculus on the root surface. With the same instrument, the trainee removes plaque and calculus from below the gum line. The third one may be employed to determine if the calculus has been completely removed. The periodontal explorer is also used to evaluate the area of the root surface covered by the gingiva to assess for the presence of dental caries on the root surface, assess abnormalities in root morphology and evaluate the presence of improperly finished dental restorative margins (Luciano, 2006). The system presented in (Wang et al, 2003) simulates two operations used in surgical dental training: probing and cutting using a high-speed rotating tool. These are essentially performed in cavity preparation and other procedures. The cutting tool is simplified to the geometry of a sphere. The centre of the sphere is corresponding to the top of a Phantom stylus. The cutting procedure for tooth preparation is also simulated by the system proposed in (Rhienmora et al, 2008). The trainee performs the cutting operation with a cylindrical bur on one of three of maxilla (upper) teeth. The system has been enhanced to include: a) a virtual mirror that is optionally controlled by a second haptic device; and b) a video see-through head-mounted display (HMD) with an attached monocular camera. Real-time head tracking is made possible by continuously grabbing camera images, detecting augmented reality markers, and registering the 3D tooth accordingly (Rhienmora et al, 2010). The same cutting procedure of a tooth is simulated by the HAP-DENT system (Yoshida et al, 2011). The procedure is performed by a trainee that uses the stylus of a haptic device to control the bar mounted on a turbine and to feel a feedback force. Preparation of primary tooth stump is an important skill for performing the dental restorations. The other skills needed to prepare teeth for ceramic crowns are given in the paper (Bogdan and Popovici, 2011). Acquiring these skills by trainees is the main objective of using the virtual and augmented reality technologies in therapeutic interventions simulation in the fixed prosthodontics (VirDenT) system. The dental instruments (such as turbine and counter-angle hand piece with multiplication) needed in all-ceramic prosthetic restorations were modelled. To date, a trainee can carry out the procedure only on the virtual central incisor, but in the near future the procedure will be realized on other two teeth: first premolar and first molar. 3. Simulators Evaluation Most of the dental simulators reviewed in the previous section have been evaluated by trainees, novices and/or experts. The evaluation objective is to prove the effectiveness of the system for training tactile skills to dental students. Table 1 summarizes the results of the evaluation of some previously reviewed visuo-haptic simulators.
6 60 University of Bucharest and "Babeş-Bolyai" University of Cluj-Napoca Table 1. The results of the evaluation of some visuo-haptic dental simulators Visuo-haptic simulator IDSS (Konukseven et al, 2010) PerioSim Periodontal simulator Assessment procedure Questionnaire with 10 items related to the realism of the simulator execution, the usage of the haptic stylus and the importance of different improvements to the simulator. Questionnaire with 25 items intended to measure the usability, clarity, effectiveness, supportive-ness of the system and satisfaction of the users. Questionnaire with 36 items intended to measure the realism of the simulation and the usefulness of this kind of simulators (Steinberg et al, 2007). Questionnaire with 7 items and a survey with ranking questions. Number of trainees Results 12 The trainees were generally satisfied (Thomas et al, 2001). 10 The system needs further improve-ments (Konukseven et al, 2010). 30 The simulation is realistic, excepting the visuo-haptic ren-dering of the gingi-val soft tissues. 43 The virtual reality environment and haptic feedback were realistic enough to serve as a useful instruction tool with high teaching potential on periodontal procedures (Luciano, 2006). 4. Conclusion The evaluation results showed that the visuo-haptic simulators may help trainees to develop their dental skills. However, in order to assure the realism of the dental procedures simulated, more hard work is required to develop the visual and haptic components of the simulator and to properly synchronize them. Acknowledgments This review was supported by the project VirDenT, which is funded by the Romanian National Centre for Project Management in the 2008 competition with the number PNII References Bogdan, C.M., Popovici, D.M. (2011): Information system analysis of an e-learning system used for dental restorations simulation, Comput. Methods Programs Biomed., in press. Buchanan, J. A. (2001): Use of Simulation Technology in Dental Education, Journal of Dental Education, 65, 11, Iowa Dental Surgical Simulator, accessed: August, Jasinevicius, T.R., Landers, M., Nelson, S., Urbankova, A. (2004): An Evaluation of Two Dental Simulation Systems: Virtual Reality versus Contemporary Non-Computer-Assisted, Journal of Dental Education, 68, 11, Kim, L., Hwang, Y., Park, S. H., Ha, S. (2005): Dental Training System using Multi-modal Interface, Computer-Aided Design & Applications, 2, 5, Konukseven, E. I., Önder, M. E., Mumcuoglu, E., Kisnisci, R. S. (2010): Development of a Visio-Haptic Integrated Dental Training Simulation System, Journal of Dental Education, 74, 8, Leblanc, V. R., Urbankova, A., Hadavi, F., Lichtenthal, R. M. (2004): A preliminary study in using virtual reality to train dental students, Journal of Dental Education, 68, 3,
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