Haptic Simulation of Organ Deformation and 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.