Simodont ® haptic dental simulator

The Moog Simodont® dental trainer is a virtual reality haptic dental simulator developed by Moog Inc. (Nieuw-Vennep, Amsterdam, Netherlands) and ACTA (the Academic Centre for Dentistry, Amsterdam, the Netherlands). The

Simodont® device consists of a training console with haptic interface and an attached computer screen.

3.2.1.1 The haptic interface

The key feature of any haptic interface is that it allows user interaction with the virtual environment via simulated sensory information and force feedback that allow touch and manipulation of three-dimensional objects.

Simodont’s® _{haptic interface provides force feedback based on the admittance} control paradigm (for details see page 32,33 ) of the HapticMaster (Moog Inc. 2011) ( Figure 2-6,B), through which the simulator responds to force exerted

by the user, leading to a sense that the user is interacting with an object of equal mass.

The simulator comprises of two separate, varied frequency loops (haptic and graphics). The simulation of tooth cutting and collision detection runs via the haptic loop so that the realistic force feedback in tooth cutting simulation is computed within 1 millisecond. The force feedback robotic arm is connected to the courseware so that every movement is visualised on the attached

computer screen (Bakker et al. 2010).

3.2.1.2 Simulator Screen

The training console of the simulator consists of a small screen (5” size with a 60Hz refresh rate and 800x600 resolution) located in front of the trainee so that it simulates the patients’ head position. Underneath the screen is a

physical handpiece with a virtual tip, and dental mirror handle with virtual head. The screen size is ‘life-sized’ and accurately seen in the physical workspace of the hand piece, which is mirrored in the co-located visual display (Moog Inc. 2016). The high-resolution stereo image with real size co-located visual display (approximating the human eye acuity limits) is facilitated by 3D projection and mirror technology. Magnification (zoom in/out) of the 3D display is possible up to 125% in the current settings used with all participants in our studies, but can be increased up to 300%, similarly, the full rotation of the virtual models in the 3D display is possible.

3.2.1.3 Stereoscopic display

To obtain the 3D stereoscopic vision in Simodont®, the simulator is equipped with two digital multimedia projectors from LG™ (type HS101, resolution 800X600), which operate simultaneously resulting in projection of two images

superimposed onto the screen through a polarizing filter. The operator needs to wear passive polarised glasses for the image to be perceived as one 3D image (de Boer et al. 2016a).

For the 2D vision in Simodont®, one of the projectors can be turned off, and in our stereopsis experiment (Chapter 5, section 5.2 ) we asked the participants to wear another type of glasses (non polarized lightly tinted glasses) to perform the tasks under 2D conditions. The simulator was engineered to output a single image (to both eyes) within the non-stereoscopic conditions.

3.2.1.4 Courseware

A separate computer is attached to the Simodont® training console and it contains a specialised courseware (developed by ACTA), with two

components: the virtual clinic and the virtual lab.

The courseware comprises lesson programs and modules with a range of manual dexterity exercises, operative dentistry procedures, as well as crown and bridge cases, all with varied levels of difficulty. The manual dexterity module offers automatic evaluation and records the real-time kinematics of student performance, which appears on the attached computer screen and shows all the recorded metrics in detail (e.g. the percentage of the target removed, the percentage of errors done to the sides and bottom of the shape). Therefore, the participant will be able to monitor his/her progress in real-time. The available teeth library is derived from real extracted teeth. The volumetric data of the teeth is acquired via i-CAT™ scanner - a specialised cone beam Computed Tomography technology for dental CT scans (Imaging Sciences International, LLC) (Bakker et al. 2010). The varied force feedback of the virtual teeth is based on the density values of the manipulated dental tissue;

for example enamel is harder to remove than soft carious dentin. The virtual teeth library is expandable and editable, allowing for the addition of various shapes and sizes of virtual teeth with and without pathology (de Boer et al. 2013), with unlimited practice possibilities using imported dental cases of varied complexity, contributed by some dental schools including ACTA and Leeds School of Dentistry (Moog Inc. 2016).

3.2.1.5 Virtual handpiece and instruments

Hand instruments are simulated (true to size) as well as various types of dental bur (diamond, tungsten carbide and steel). Dental mirror allows the realistic examination of the teeth from all sides, in addition to other instruments such as dental explorer with force feedback. The dental tools have six degrees of freedom positional sensing, generating three degrees of freedom force feedback (Bakker et al. 2010).

The speed of the virtual hand piece is controlled using a realistic foot pedal. Once the operator presses the foot pedal the handpiece operates with a realistic air turbine (rotor) sound and the dental bur starts revolving. Once the bur comes in contact with the block or the virtual tooth the cutting takes place providing that the participant presses on a specific area of the virtual tooth. When a virtual tooth is cut, multimodal simultaneous visual, audio and tactile feedback are received (de Boer et al. 2013).

Figure 3-1 Simodont® simulator device with labelled components. Image courtesy of Moog (Moog Inc. 2011).

Handpiece

Virtual movement controller/mouse Dental mirror handle

Power button

Screen vertical level controller Foot pedal Computer panel Stereoscopic display screen Multimedia Projector

Figure 3-2 Simodont® trainee perspective showing the co-located visual

display as the screen appears in the physical workspace of the handpiece and the mirror. Image courtesy of Moog (Moog Inc. 2011).