Dangxiao Wang

iDental: A Haptic-Based Dental Simulator and Its Preliminary User Evaluation

Performance evaluation is indispensable for a surgical simulator to become acceptable. A haptics-based dental simulator (iDental) has been developed and preliminary user evaluation on its first-generation prototype has been carried out to gain the knowledge. Based on detailed requirement analysis of Periodontics procedures, a combined evaluation method including qualitative and quantitative analysis was designed. Construct validity was used to compare the performance difference between two groups of participants (faculty members and dental graduate students). These participants were required to perform three periodontal examination and treatment procedures including periodontal pocket probing, calculus detection, and removal. From the evaluation results, we found that penetration between tool and teeth or cheek will greatly decrease the fidelity of the simulation, therefore, it is necessary to utilize 6-DOF haptic device with both force and torque feedback in dental simulator, and accordingly it is needed to extend point-based rendering to 6-DOF haptic rendering of multiregion contacts. Furthermore, several other key research topics that will enable haptic technology to be effective in a practical dental simulator were identified, including simulation of deformable body such as tongue and gingival, and simulation of occlusion of tongue and cheek on teeth, etc.Performance evaluation is indispensable for a surgical simulator to become acceptable. A haptics-based dental simulator (iDental) has been developed and preliminary user evaluation on its first-generation prototype has been carried out to gain the knowledge. Based on detailed requirement analysis of Periodontics procedures, a combined evaluation method including qualitative and quantitative analysis was designed. Construct validity was used to compare the performance difference between two groups of participants (faculty members and dental graduate students). These participants were required to perform three periodontal examination and treatment procedures including periodontal pocket probing, calculus detection, and removal. From the evaluation results, we found that penetration between tool and teeth or cheek will greatly decrease the fidelity of the simulation, therefore, it is necessary to utilize 6-DOF haptic device with both force and torque feedback in dental simulator, and accordingly it is needed to extend point-based rendering to 6-DOF haptic rendering of multiregion contacts. Furthermore, several other key research topics that will enable haptic technology to be effective in a practical dental simulator were identified, including simulation of deformable body such as tongue and gingival, and simulation of occlusion of tongue and cheek on teeth, etc.

Configuration-Based Optimization for Six Degree-of-Freedom Haptic Rendering for Fine Manipulation

Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. We represent an object using a hierarchy of spheres, i.e., a sphere tree, which allows faster detection of multiple contacts/collisions among objects than polygonal mesh and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we compute its quasi-static motion by solving a configuration-based optimization. The constraints in the 6D configuration space of the graphic tool is obtained and updated through online mapping of the nonpenetration constraint between the spheres of the graphic tool and those of the other objects in the three-dimensional physical space, based on the result of collision detection. This problem is further modeled as a quadratic programming optimization and solved by the classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DOF Phantom Premium 3.0. We demonstrate its performance in several benchmarks involving complex, multiregion contacts. The experimental results show both the high efficiency and stability of haptic rendering by our method for complex scenarios. Nonpenetration between the graphic tool and the object is maintained under frequent contact switches. Update rate of the simulation loop including optimization and constraint identification is maintained at about 1 kHz.Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. We represent an object using a hierarchy of spheres, i.e., a sphere tree, which allows faster detection of multiple contacts/collisions among objects than polygonal mesh and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we compute its quasi-static motion by solving a configuration-based optimization. The constraints in the 6D configuration space of the graphic tool is obtained and updated through online mapping of the nonpenetration constraint between the spheres of the graphic tool and those of the other objects in the three-dimensional physical space, based on the result of collision detection. This problem is further modeled as a quadratic programming optimization and solved by the classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DOF Phantom Premium 3.0. We demonstrate its performance in several benchmarks involving complex, multiregion contacts. The experimental results show both the high efficiency and stability of haptic rendering by our method for complex scenarios. Nonpenetration between the graphic tool and the object is maintained under frequent contact switches. Update rate of the simulation loop including optimization and constraint identification is maintained at about 1 kHz.

Haptic rendering for dental training system

Immersion and interaction are two key features of virtual reality systems, which are especially important for medical applications. Based on the requirement of motor skill training in dental surgery, haptic rendering method based on triangle model is investigated in this paper. Multi-rate haptic rendering architecture is proposed to solve the contradiction between fidelity and efficiency requirements. Realtime collision detection algorithm based on spatial partition and time coherence is utilized to enable fast contact determination. Proxy-based collision response algorithm is proposed to compute surface contact point. Cutting force model based on piecewise contact transition model is proposed for dental drilling simulation during tooth preparation. Velocity-driven levels of detail haptic rendering algorithm is proposed to maintain high update rate for complex scenes with a large number of triangles. Hapticvisual collocated dental training prototype is established using half-mirror solution. Typical dental operations have been realized including dental caries exploration, detection of boundary within dental cross-section plane, and dental drilling during tooth preparation. The haptic rendering method is a fundamental technology to improve immersion and interaction of virtual reality training systems, which is useful not only in dental training, but also in other surgical training systems.

Toward Force-Based Signature Verification: A Pen-Type Sensor and Preliminary Validation

A compact pen-type force sensor is developed to study the feasibility of force-based signature verification. A force-sensing method based on leverage effect is proposed to detect 3-D forces between the pens tip and the paper. A compact and low-cost force-sensing assembly is designed, which is integrated by five off-the-shelf 1-D force sensors. A matrix-based measurement model is established to compute the force signal in the task coordinate system (CS), which is transformed from the force signal in the sensor CS and the angle signal from a 2-D angle sensor. The structural parameters of the force sensor are determined both to achieve the required force accuracy and to meet the constraints of pen size for comfortable grasping. System performance experiments are carried out to measure the absolute and repetitive accuracy of the pen. The results show that the pen is capable for detection of 3-D force signals during real-time handwriting. Repetitive accuracy is measured to be about 0.05 N. Finally, a small-scale signature verification experiment is carried out. The verification results based on the dynamic time warping (DTW) method show that the equal error rate (EER) is about 6.3%, which illustrates the potential of the pen for force-based signature verification.

Toward Stable and Realistic Haptic Interaction for Tooth Preparation Simulation

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. DOI: 10.1115/1.3402759

VOXEL-BASED INTERACTIVE HAPTIC SIMULATION OF DENTAL DRILLING

Haptics is one of the most important sensations for dentists to prepare cavity in dental surgery, which is however not easy to simulate in a computer system because of the large drilling force and the small speed of movement and material removal. In this paper, we present a fully voxel-based approach to interactively simulate dental drilling. Different from those voxel/mesh hybrid models, the drilling forces are computed directly from the voxel-representation while considering the factors of teeth’s material properties, the posture and forward speed of dentist’s drill and the contact surface area. To overcome force discontinuity caused by removal of tooth material, we define two layers of voxels on drill, where the boundary voxels are only employed to compute force feedback and the interior voxels are adopted to remove materials from teeth. The experimental result shows that our force model can produce smooth and large force feedback at a slow movement on haptic devices. Other than haptic rendering, a real-time filtering method directly using voxel representation has also been developed to improve visual rendering in dental simulation.Copyright

Development of dental training system with haptic display

This paper discusses the development of a dental training system with haptic display capability. The system architecture is proposed firstly concerning two typical operations, probing and cutting, in dental surgery. Triangle mesh model is used for the tooth to reduce the computation time. Real time collision detection is realized between the tooth and a spherical tool. The operation force is determined from the penetration between the tool and the tooth. Material removal from the tooth is realized using vertex deformation method. Force filtering approach is proposed to eliminate vibration of the haptic device. Experiment results show that the system can provide stable simulation of probing and cutting operation.

Configuration-based optimization for six degree-of-freedom haptic rendering for fine manipulation

Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. We represent an object using a hierarchy of spheres, i.e., a sphere tree, which allows faster detection of multiple contacts/collisions among objects than polygonal mesh and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we compute its quasi-static motion by solving a configuration-based optimization. The constraints in the 6D configuration space of the graphic tool is obtained and updated through online mapping of the nonpenetration constraint between the spheres of the graphic tool and those of the other objects in the three-dimensional physical space, based on the result of collision detection. This problem is further modeled as a quadratic programming optimization and solved by the classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DOF Phantom Premium 3.0. We demonstrate its performance in several benchmarks involving complex, multiregion contacts. The experimental results show both the high efficiency and stability of haptic rendering by our method for complex scenarios. Nonpenetration between the graphic tool and the object is maintained under frequent contact switches. Update rate of the simulation loop including optimization and constraint identification is maintained at about 1 kHz.

Haptic Simulation of Organ Deformationand Hybrid Contacts in Dental Operations

There are two main challenges in simulating bi-manual dental operations with six-degrees-of-freedom (6-DoF) haptic rendering. One is to simulate large deformation and force response of a tongue under multi-region contacts with a dental mirror, and the other is to simulate the force response when a dental probe inserts into a narrow periodontal pocket, which leads to simultaneous contacts of different types between the probe and both rigid and deformable objects (i.e., a rigid tooth and its surrounding deformable gingiva), which we call hybrid contacts, as well as frequent contact switches. In this paper, we address both challenges. We first introduce a novel method for modeling deformation based on a sphere-tree representation of deformable objects. A configuration-based constrained optimization method is utilized for determining the six-dimensional configuration of the graphic tool and the contact force/torque. This approach conducts collision detection, deformation computation, and tool configuration optimization very efficiently, avoids inter-penetration, and maintains stability of haptic display without using virtual coupling. To simulate the force response due to fine manipulation of the probe inside a narrow periodontal pocket, we propose an efficient method to simulate the local deformation of the gingiva and stable haptic feedback under frequent contact switches. Simulations on typical dental operations were carried out to validate the efficiency and stability of our approach.

Configuration-based optimization for six degree-of-freedom haptic rendering using sphere-trees

This paper presents a novel constraint-based six degree-of-freedom (6-DoF) haptic rendering algorithm for simulating both contact forces and torques between interacting rigid bodies. We represent an object using a hierarchy of spheres, i.e., a sphere-tree. Such a representation allows fast detection of multiple contacts/collisions among objects and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we constrain its position and orientation, i.e., its six dimensional configuration, by solving a constrained optimization problem. The constraints in the 6-D configuration space (C-space) of the graphic tool is obtained and updated through on-line mapping of the non-penetration constraint between the spheres of the graphic tool and those of the other objects in the three dimensional physical space, based on the result of collision detection. The problem is further modeled as a quadratic programming problem and solved by classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DoF Phantom Premium 3.0. We demonstrate its performance in dental surgery simulations involving complex, multi-contact virtual environments. Our method enables stable operations and realistic feel of haptic sensation.