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Realistic haptic interaction for computer simulation of dental surgery
International Congress Series 1268 (2004) 1226 – 1229
www.ics-elsevier.com
Realistic haptic interaction for computer simulation of dental surgery M. Heiland a,*, A. Petersik b, B. Pflesser b, U. Tiede b, Rainer Schmelzle a, K.-H. Ho¨hne b, H. Handels b a
Department of Oral and Maxillofacial Surgery, University Hospital Hamburg-Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany b Institute of Medical Informatics, University Hospital Hamburg-Eppendorf, Hamburg, Germany
Abstract. Using the VOXEL-MAN system, a virtual three-dimensional (3D) model of a skull was created based on CT data. To achieve a realistic drilling effect with the force feedback system, special tools were integrated into VOXEL-MAN to obtain a high resolution of collision recognition. Using apicectomies as examples, realistic simulation of dental surgical procedures, even in complex anatomical models, was possible. The simulation of apicectomies was evaluated by 40 dental students. D 2004 CARS and Elsevier B.V. All rights reserved. Keywords: Apicectomy; 3D computer model; Virtual surgery
1. Introduction Defined reduction of bone without injuring therein lying structures is an essential part of surgical techniques, especially during dental surgery. A computer-based simulator with haptic feedback could reduce cost and offer new training possibilities. However, due to extremely demanding computational requirements, haptic rendering of high-detailed anatomic models together with interactive techniques for reduction of bone is still a challenge. Based on the previously described VOXEL-MAN software [1,2], we portray new algorithms which, on one hand, allow for realistic haptic rendering of even very small anatomic structures and on the other hand are capable of simulating the reduction of bone with realistic haptic sensations. This system has already been introduced in simulating petrous bone surgery [3]. As a new application, it was advanced for simulating dental surgical procedures [4]. Virtual apicectomies were evaluated by 40 clinical dental students. 2. Materials and methods From CT data, a virtual three-dimensional (3D) model of a skull was created. Both inferior alveolar nerves and apical inflammations of teeth 23, 25, 36, 35 were modelled. * Corresponding author. Tel.: +49-40-42803-8163; fax: +49-40-42803-5467. E-mail address: [email protected] (M. Heiland). 0531-5131/ D 2004 CARS and Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.03.132
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The visualization was done by a ray-casting algorithm which rendered isosurfaces directly from the segmented volume data at subvoxel resolution (Fig. 1). To get haptic feedback while touching the bone with a virtual tool, a multipoint collision detection approach was developed, which adequately considered shape and extend of the tool and, most important, was not limited to the resolution of properties. This information, together with the drilling direction, was used to calculate the underlying voxel data. The resolution enhancement was achieved by using the same subvoxel algorithm as for the visualization. This lead to a congruent graphic and haptic display. Because collisions were not detectable for regions of the model which were currently modified, we developed a ‘‘look forward’’ approach which was used while drilling. This approach detected collisions in front of the virtual tool, to determine material distributions and resulting drilling force. Additionally, vibrations were modulated onto the force to further enhance the sensation of drilling. The system was implemented on different PCs, ranging from a dual AthlonMP 1900+ to a dual XEON 3GHz. The PCs were equipped with at least 1 GB DDRAM. As haptic device, we used a Phantom Premium 1.0 A resp. a Phantom Desktop device (Sensable Technologies) with 3 active degrees of freedom (for position) and 3 passive degrees of freedom (for orientation). As operating system, RedHat Linux was used. To control the devices from Linux, we used Sensable’s Ghost for Linux. For stereoscopic viewing Nvidia Quadro4 750XGL boards in combination with ELSA Revelator shutter glasses were integrated. All algorithms worked with update rates of 3000 Hz which enabled a stable haptic rendering of hard surfaces like bone. Two working stations were available for free tuition offered to clinical dental students. Forty dental students (23 female and 17 male) of the last year performed virtual apicectomies
Fig. 1. 3D model for virtual dental surgery. Surface view (A) and magnified view of modelled apical inflammations and left inferior alveolar nerve after hiding the bone (B). In reality, views are available in colour.
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Fig. 2. Scoring results regarding the complexity of the presented model by 40 dental students. 1: too simple. . . 3: perfect. . .5: too complex.
in small groups of four to six persons. Evaluation of this new teaching modality was performed with the help of a questionnaire using ranking scales. 3. Results The presented simulation system allowed the visual and haptic observation of complex volume based models and virtual interaction with them. The performed drilling routes were assessable both on the 3D model unveiling the route and on axial, coronal and sagittal CT reconstructions during and after the procedure. Forty dental students performed virtual apicectomies and evaluated the simulation by filling in questionnaires. The handling of the working station proved to be easy. Offering virtual training possibilities to dental students was reported to be a very valuable addition to existing teaching modalities of dental surgery. In addition, descriptive analysis revealed complexity of the used model, resolution, force feedback simulation and haptic observation of the presented computer model to be very suitable for virtual simulation of dental surgical procedures. As an example, scoring results of the evaluation of the complexity of the used model are shown (Fig. 2). However, most mentioned criticism was the lack of soft tissue simulation and the desired inclusion of further procedures like removal of impacted third molars. 4. Discussion With the example of apicectomy, we have shown that realistic simulation of dental surgical procedures, even in complex anatomical models, is possible. The computer model has been offered to clinical dental students whose feedback was very encouraging to extend the availability of this new teaching modality. According to Alessi [5] who advised not to use very complex models for beginners, the used model was limited to the relevant structures. The scoring results confirmed the appropriate proportion between complexity
M. Heiland et al. / International Congress Series 1268 (2004) 1226–1229
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and students’ practical experiences. In principle, it is possible to add virtual pathologies in data sets and/or to use further patient data sets to extend the range of simulated surgical procedures. In future, it will be possible not only to import CT or MRI data sets, but also to use data of cone beam computed tomography systems like the NewTom 9000 which is the preferred 3D imaging modality of oral pathologies [6]. Furthermore, using micro-CT data sets of single teeth will enable the realistic simulation of tooth preparations. References [1] K.H. Ho¨hne, et al., A new representation of knowledge concerning human anatomy and function, Nat. Med. 1 (1995) 506 – 511. [2] R. Schubert, et al., Applications and perspectives in anatomical 3-dimensional modelling of the visible human with VOXEL-MAN, Acta Anat. 160 (1997) 123 – 131. [3] R. Leuwer, B. Pflesser, M. Urban, Die stereoskopische Simulation ohrchirurgischer Eingriffe an einem neuartigen Computermodell, Laryngo-Rhino-Otol. 80 (2001) 298 – 302. [4] M. Heiland, et al., Virtuelle Simulation dentoalveola¨rer Eingriffe in einem dreidimensionalen Computermodell mit Kraftru¨ckkopplungssystem Mund Kiefer GesichtsChir. (in press). [5] S.M. Alessi, Fidelity in the design of instructional simulations, J. Comput. Instr. 15 (1988) 40 – 47. [6] M. Heiland, et al., Midfacial imaging using digital volume tomography, in: H.U. Lemke, M.V. Vannier, K. Inamura, A.G. Farman, K. Doi, J.H.C. Reiber (Eds.), CARS 2003—Proceedings of the 17th International Congress and Exhibition: Computer Assisted Radiology and Surgery, Excerpta Medica International Congress Series, vol. 1256, Elsevier, Amsterdam, 2003, pp. 1230 – 1234.
www.ics-elsevier.com
Realistic haptic interaction for computer simulation of dental surgery M. Heiland a,*, A. Petersik b, B. Pflesser b, U. Tiede b, Rainer Schmelzle a, K.-H. Ho¨hne b, H. Handels b a
Department of Oral and Maxillofacial Surgery, University Hospital Hamburg-Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany b Institute of Medical Informatics, University Hospital Hamburg-Eppendorf, Hamburg, Germany
Abstract. Using the VOXEL-MAN system, a virtual three-dimensional (3D) model of a skull was created based on CT data. To achieve a realistic drilling effect with the force feedback system, special tools were integrated into VOXEL-MAN to obtain a high resolution of collision recognition. Using apicectomies as examples, realistic simulation of dental surgical procedures, even in complex anatomical models, was possible. The simulation of apicectomies was evaluated by 40 dental students. D 2004 CARS and Elsevier B.V. All rights reserved. Keywords: Apicectomy; 3D computer model; Virtual surgery
1. Introduction Defined reduction of bone without injuring therein lying structures is an essential part of surgical techniques, especially during dental surgery. A computer-based simulator with haptic feedback could reduce cost and offer new training possibilities. However, due to extremely demanding computational requirements, haptic rendering of high-detailed anatomic models together with interactive techniques for reduction of bone is still a challenge. Based on the previously described VOXEL-MAN software [1,2], we portray new algorithms which, on one hand, allow for realistic haptic rendering of even very small anatomic structures and on the other hand are capable of simulating the reduction of bone with realistic haptic sensations. This system has already been introduced in simulating petrous bone surgery [3]. As a new application, it was advanced for simulating dental surgical procedures [4]. Virtual apicectomies were evaluated by 40 clinical dental students. 2. Materials and methods From CT data, a virtual three-dimensional (3D) model of a skull was created. Both inferior alveolar nerves and apical inflammations of teeth 23, 25, 36, 35 were modelled. * Corresponding author. Tel.: +49-40-42803-8163; fax: +49-40-42803-5467. E-mail address: [email protected] (M. Heiland). 0531-5131/ D 2004 CARS and Elsevier B.V. All rights reserved. doi:10.1016/j.ics.2004.03.132
M. Heiland et al. / International Congress Series 1268 (2004) 1226–1229
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The visualization was done by a ray-casting algorithm which rendered isosurfaces directly from the segmented volume data at subvoxel resolution (Fig. 1). To get haptic feedback while touching the bone with a virtual tool, a multipoint collision detection approach was developed, which adequately considered shape and extend of the tool and, most important, was not limited to the resolution of properties. This information, together with the drilling direction, was used to calculate the underlying voxel data. The resolution enhancement was achieved by using the same subvoxel algorithm as for the visualization. This lead to a congruent graphic and haptic display. Because collisions were not detectable for regions of the model which were currently modified, we developed a ‘‘look forward’’ approach which was used while drilling. This approach detected collisions in front of the virtual tool, to determine material distributions and resulting drilling force. Additionally, vibrations were modulated onto the force to further enhance the sensation of drilling. The system was implemented on different PCs, ranging from a dual AthlonMP 1900+ to a dual XEON 3GHz. The PCs were equipped with at least 1 GB DDRAM. As haptic device, we used a Phantom Premium 1.0 A resp. a Phantom Desktop device (Sensable Technologies) with 3 active degrees of freedom (for position) and 3 passive degrees of freedom (for orientation). As operating system, RedHat Linux was used. To control the devices from Linux, we used Sensable’s Ghost for Linux. For stereoscopic viewing Nvidia Quadro4 750XGL boards in combination with ELSA Revelator shutter glasses were integrated. All algorithms worked with update rates of 3000 Hz which enabled a stable haptic rendering of hard surfaces like bone. Two working stations were available for free tuition offered to clinical dental students. Forty dental students (23 female and 17 male) of the last year performed virtual apicectomies
Fig. 1. 3D model for virtual dental surgery. Surface view (A) and magnified view of modelled apical inflammations and left inferior alveolar nerve after hiding the bone (B). In reality, views are available in colour.
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M. Heiland et al. / International Congress Series 1268 (2004) 1226–1229
Fig. 2. Scoring results regarding the complexity of the presented model by 40 dental students. 1: too simple. . . 3: perfect. . .5: too complex.
in small groups of four to six persons. Evaluation of this new teaching modality was performed with the help of a questionnaire using ranking scales. 3. Results The presented simulation system allowed the visual and haptic observation of complex volume based models and virtual interaction with them. The performed drilling routes were assessable both on the 3D model unveiling the route and on axial, coronal and sagittal CT reconstructions during and after the procedure. Forty dental students performed virtual apicectomies and evaluated the simulation by filling in questionnaires. The handling of the working station proved to be easy. Offering virtual training possibilities to dental students was reported to be a very valuable addition to existing teaching modalities of dental surgery. In addition, descriptive analysis revealed complexity of the used model, resolution, force feedback simulation and haptic observation of the presented computer model to be very suitable for virtual simulation of dental surgical procedures. As an example, scoring results of the evaluation of the complexity of the used model are shown (Fig. 2). However, most mentioned criticism was the lack of soft tissue simulation and the desired inclusion of further procedures like removal of impacted third molars. 4. Discussion With the example of apicectomy, we have shown that realistic simulation of dental surgical procedures, even in complex anatomical models, is possible. The computer model has been offered to clinical dental students whose feedback was very encouraging to extend the availability of this new teaching modality. According to Alessi [5] who advised not to use very complex models for beginners, the used model was limited to the relevant structures. The scoring results confirmed the appropriate proportion between complexity
M. Heiland et al. / International Congress Series 1268 (2004) 1226–1229
1229
and students’ practical experiences. In principle, it is possible to add virtual pathologies in data sets and/or to use further patient data sets to extend the range of simulated surgical procedures. In future, it will be possible not only to import CT or MRI data sets, but also to use data of cone beam computed tomography systems like the NewTom 9000 which is the preferred 3D imaging modality of oral pathologies [6]. Furthermore, using micro-CT data sets of single teeth will enable the realistic simulation of tooth preparations. References [1] K.H. Ho¨hne, et al., A new representation of knowledge concerning human anatomy and function, Nat. Med. 1 (1995) 506 – 511. [2] R. Schubert, et al., Applications and perspectives in anatomical 3-dimensional modelling of the visible human with VOXEL-MAN, Acta Anat. 160 (1997) 123 – 131. [3] R. Leuwer, B. Pflesser, M. Urban, Die stereoskopische Simulation ohrchirurgischer Eingriffe an einem neuartigen Computermodell, Laryngo-Rhino-Otol. 80 (2001) 298 – 302. [4] M. Heiland, et al., Virtuelle Simulation dentoalveola¨rer Eingriffe in einem dreidimensionalen Computermodell mit Kraftru¨ckkopplungssystem Mund Kiefer GesichtsChir. (in press). [5] S.M. Alessi, Fidelity in the design of instructional simulations, J. Comput. Instr. 15 (1988) 40 – 47. [6] M. Heiland, et al., Midfacial imaging using digital volume tomography, in: H.U. Lemke, M.V. Vannier, K. Inamura, A.G. Farman, K. Doi, J.H.C. Reiber (Eds.), CARS 2003—Proceedings of the 17th International Congress and Exhibition: Computer Assisted Radiology and Surgery, Excerpta Medica International Congress Series, vol. 1256, Elsevier, Amsterdam, 2003, pp. 1230 – 1234.