  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.
