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Research Papers

Toward Stable and Realistic Haptic Interaction for Tooth Preparation Simulation

[+] Author and Article Information
Jun Wu

State Key Laboratory of Virtual Reality Technology and Systems, Beihang University, 100191 Beijing, P.R.C.;wujun@me.buaa.edu.cnDepartment of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, P.R.C.wujun@me.buaa.edu.cn

Dangxiao Wang, Yuru Zhang

State Key Laboratory of Virtual Reality Technology and Systems, Beihang University, 100191 Beijing, P.R.C.

Charlie C. L. Wang1

Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, P.R.C.cwang@mae.cuhk.edu.hk

1

Corresponding author.

J. Comput. Inf. Sci. Eng 10(2), 021007 (Jun 03, 2010) (9 pages) doi:10.1115/1.3402759 History: Received October 13, 2009; Revised March 01, 2010; Published June 03, 2010; Online June 03, 2010

In this paper, we present the methods to generate a stable and realistic simulator for dental surgery. First, a simplified force model is derived from grinding theory by considering the complex bur shape and dental handpiece’s dynamic behavior. While the force model can be evaluated very fast to fulfill the high update rate of haptic rendering, it also explains basic haptic sensation features in tooth preparation operation. Second, as direct rendering of this damping-like force model may induce instability of the haptic device, we apply a virtual coupling based method to guarantee the stability in haptic rendering. Furthermore, implicit integration of the bur’s motion equation is utilized to ensure numerical stability. Third, to overcome force discontinuity caused by locally removing tooth materials, we define a two-layer based representation for the bur, where the boundary voxels are adopted to compute forces and the interior voxels are employed to remove materials from teeth. The experimental results agree with the real sensation described by experienced dentists.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Dental surgery training in medical schools on real removed teeth on a dummy head

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Figure 2

Burs in different shapes are employed in dental treatments

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Figure 3

The illustration of tooth subsections (captured in Ref. 24)

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Figure 4

A typical grinding process. The grinding force is divided into normal grinding force Fn and tangential grinding force Ft.

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Figure 5

Force analysis on the surface of bur

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Figure 6

Virtual coupling scheme: The virtual bur is coupled with the haptic handle through a viscoelastic/elastic spring and the motion of virtual bur is governed by the coupling force and the grinding force

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Figure 7

Material removal: (a) the status at the time current t=ti and (b) the status at t=ti+1 where three voxels in the tooth have been removed. However, the contact area is constant during the material removal. For giving a better illustration, internal voxels of the bur are not displayed in (b).

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Figure 8

The left picture shows the training scenario. The internal physical structure of the platform can be found in the right picture, which consists of a computer monitor, two haptic devices, and a half-silvered mirror to co-locate the virtual environment and real hands.

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Figure 9

The specific grinding energy u of the hard enamel is 0.3 J/mm3 and the energy 0.1 J/mm3 is for the inner soft dentin. The hard enamel and the soft dentin are shown in different color in the right. The right picture shows the resultant geometry of grinding.

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Figure 10

The magnitude of velocity in y-direction is increasing when vertically moving a cylinder bur to the surface of a tooth. The resultant grinding forces (Fx,Fy) and torque (Tz) are proportional to the change in velocity.

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Figure 11

Grinding with decreased contact area during the simulation. The resultant grinding forces and torque are proportional to the contact area.

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Figure 12

Grinding using a ball bur. The trend of the forces and torque generated by using a ball bur is similar to that generated by using a cylinder bur (as in Fig. 9). The right picture shows resulting geometry using a ball bur, different from that of using a cylinder bur (as in Fig. 9).

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Figure 13

Virtual coupling based grinding on two different materials. Compared with direct force calculation in Fig. 9, the voxel effect has been eliminated.

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Figure 14

Grinding with increasing forward velocity. At first, the coupling force and torque increase proportional to the value of velocity. When the torque exceeds the stall torque, we stop moving the virtual bur even if the coupling force increases sharply.

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Figure 15

Forces generated by different approaches—direct rendering versus virtual coupling based rendering. In the interactive test, the virtual coupling based approach provides more stable feedback force than the direct rendering.

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Figure 16

The results by using our system: left—the original teeth; right—preparing the crown to mount fake teeth (top row); the prepared class II cavity (middle row); and the prepared class I cavity (bottom row)

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