Abstract
Within the orthodontics instrumentation community, many different sensing schemes have been developed over decades for purposes of characterizing the movement of the mandible. Such information can be very useful in the diagnosis and treatment of problems such as the dental occlusion. An overview of multiple optical devices is provided and we focus specifically on intriguing kinematic processing issues associated with a device referred to as a “Mandibular Position Indicator,” invented by Roger Evenson. At the heart of the sensing scheme are 2 bow systems (upper, lower) with LASERS (4 total) fixed to the lower bow system with image plane patches and cameras fixed with respect to the skull. Measurement of the coordinates of the LASER spots in image plane coordinate frames with static registration characterization via appropriate 3D scans should provide enough information to permit solving for the unknown movement homogeneous transformation. Kinematic loop closure equations are formulated and they must be solved numerically. Validation was investigated with both physical and very accurate computer-aided-design (CAD) models. Due to apparent sensing redundancy, only 3 of the 4 LASER, image plane, and camera systems are needed for a very accurate solution by retaining results from the least singular hardware configuration.