Zhao Xiaohan, Zhu Zhuoli, Cong Yu, Zhao Yongtao, Zhang Yuru, Wang Dangxiao
Beijing Unidraw Virtual Reality Technology Research Institute Co. Ltd., Beijing, China.
State Key Laboratory of Oral Disease, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
Front Robot AI. 2020 Mar 20;7:35. doi: 10.3389/frobt.2020.00035. eCollection 2020.
Motor skill learning of dental implantation surgery is difficult for novices because it involves fine manipulation of different dental tools to fulfill a strictly pre-defined procedure. Haptics-enabled virtual reality training systems provide a promising tool for surgical skill learning. In this paper, we introduce a haptic rendering algorithm for simulating diverse tool-tissue contact constraints during dental implantation. Motion forms of an implant tool can be summarized as the high degree of freedom (H-DoF) motion and the low degree of freedom (L-DoF) motion. During the H-DoF state, the tool can move freely on bone surface and in free space with 6 DoF. While during the L-DoF state, the motion degrees are restrained due to the constraints imposed by the implant bed. We propose a state switching framework to simplify the simulation workload by rendering the H-DoF motion state and the L-DoF motion state separately, and seamless switch between the two states by defining an implant criteria as the switching judgment. We also propose the virtual constraint method to render the L-DoF motion, which are different from ordinary drilling procedures as the tools should obey different axial constraint forms including sliding, drilling, screwing and perforating. The virtual constraint method shows efficiency and accuracy in adapting to different kinds of constraint forms, and consists of three core steps, including defining the movement axis, projecting the configuration difference, and deriving the movement control ratio. The H-DoF motion on bone surface and in free space is simulated through the previously proposed virtual coupling method. Experimental results illustrated that the proposed method could simulate the 16 different phases of the complete implant procedures of the Straumann® Bone Level(BL) Implants Φ4.8-L12 mm. According to the output force curve, different contact constraints could be rendered with steady and continuous output force during the operation procedures.
对于新手而言，牙种植手术的运动技能学习颇具难度，因为这需要精细操作不同的牙科工具来完成严格预定义的程序。具备触觉的虚拟现实训练系统为手术技能学习提供了一种很有前景的工具。在本文中，我们介绍一种用于模拟牙种植过程中各种工具与组织接触约束的触觉渲染算法。种植工具的运动形式可概括为高自由度（H-DoF）运动和低自由度（L-DoF）运动。在H-DoF状态下，工具可在骨表面和自由空间中以6个自由度自由移动。而在L-DoF状态下，由于种植床施加的约束，运动自由度受到限制。我们提出一种状态切换框架，通过分别渲染H-DoF运动状态和L-DoF运动状态来简化模拟工作量，并通过定义一个种植标准作为切换判断来实现两种状态之间的无缝切换。我们还提出了虚拟约束方法来渲染L-DoF运动，这与普通钻孔程序不同，因为工具应遵循不同的轴向约束形式，包括滑动、钻孔、拧螺丝和穿孔。虚拟约束方法在适应不同类型的约束形式方面显示出效率和准确性，它由三个核心步骤组成，包括定义运动轴、投影配置差异以及推导运动控制比率。骨表面和自由空间中的H-DoF运动通过先前提出的虚拟耦合方法进行模拟。实验结果表明，所提出的方法能够模拟士卓曼®骨水平（BL）种植体Φ4.8-L12 mm完整种植程序的16个不同阶段。根据输出力曲线，在操作过程中可以通过稳定且连续的输出力来呈现不同的接触约束。
