Dental simulators gained prevalence in recent years. Important aspects distinguishing VR hardware configurations are 3D stereoscopic rendering and visual alignment of the user's hands with the virtual tools. New dental simulators are often evaluated without analysing the impact of these simulation aspects. In this paper, we seek to determine the impact of 3D stereoscopic rendering and of hand-tool alignment on the teaching effectiveness and skill assessment accuracy of a VR dental simulator. We developed a bimanual simulator using an HMD and two haptic devices that provides an immersive environment with both 3D stereoscopic rendering and hand-tool alignment. We then independently controlled for each of the two aspects of the simulation. We trained four groups of students in root canal access opening using the simulator and measured the virtual and real learning gains. We quantified the real learning gains by pre- and post-testing using realistic plastic teeth and the virtual learning gains by scoring the training outcomes inside the simulator. We developed a scoring metric to automatically score the training outcomes that strongly correlates with experts' scoring of those outcomes. We found that hand-tool alignment has a positive impact on virtual and real learning gains, and improves the accuracy of skill assessment. We found that stereoscopic 3D had a negative impact on virtual and real learning gains, however it improves the accuracy of skill assessment. This finding is counter-intuitive, and we found eye-tooth distance to be a confounding variable of stereoscopic 3D, as it was significantly lower for the monoscopic 3D condition and negatively correlates with real learning gain. The results of our study provide valuable information for the future design of dental simulators, as well as simulators for other high-precision psycho-motor tasks.

翻译：牙科模拟器近年来逐渐普及。区分虚拟现实硬件配置的重要方面包括三维立体渲染和用户手部与虚拟工具之间的视觉对齐。新型牙科模拟器的评估往往未分析这些模拟方面的影响。本文旨在确定三维立体渲染及手工具对准对VR牙科模拟器教学效果和技能评估准确性的影响。我们开发了一款使用头戴式显示器（HMD）和两个触觉设备的双手模拟器，该模拟器提供包含三维立体渲染和手工具对准的沉浸式环境，随后对这两个模拟方面分别进行独立控制。我们利用该模拟器训练四组学生进行根管通路开髓操作，并测量虚拟与现实学习增益。通过使用仿真塑料牙进行前测和后测来量化现实学习增益，通过评分模拟器内的训练成果量化虚拟学习增益。我们开发了一种与专家评分高度相关的自动评分指标。研究发现，手工具对准对虚拟和现实学习增益具有积极影响，并能提高技能评估的准确性；而三维立体渲染对虚拟和现实学习增益产生负面影响，但同样能提升技能评估准确性。这一发现违反直觉，且我们发现眼-牙距离是三维立体渲染的混杂变量——单目三维条件下该距离显著更低，且与现实学习增益呈负相关。本研究结果为未来牙科模拟器及其他高精度心理运动任务模拟器的设计提供了重要参考。