4D Clinical Imaging for Dynamic CAD

A basic 4D imaging system to capture the jaw motion has been developed that produces high resolution 3D surface data. Fluorescent microspheres are brushed onto the areas of the upper and the lower arches to be imaged, producing a high-contrast random optical pattern. A hand-held imaging device operated at about 10？cm from the mouth captures time-based perspective images of the fluorescent areas. Each set of images, containing both upper and the lower arch data, is converted to a 3d point mesh using photogrammetry, thereby providing an instantaneous relative jaw position. Eight 3d positions per second are captured. Using one of the 3d frames as a reference, incremental transforms are derived to express the free body motion of the mandible. Conventional 3d models of the dentition are directly registered to the reference frame, allowing them to be animated using the derived transforms. 1. Introduction The incorporation of patient-specific motion into the CAD used for dental prosthetics remains a desirable goal. Beginning with the work of Karlsson [1], photogrammetry has been increasingly applied to the study of the mandibular motion. Photogrammetry targets have been applied to frames [2–4] and shown capable of characterizing the mandibular motion. Targets have also been attached to the teeth using a variety of methods [5–9]. An inherent problem with the use of frames and individual targets is the required registration of the dynamic clinical data to the 3D anatomy of interest. Each reported method requires a specific technique to achieve this registration. This report presents a brief description of a new mandibular imaging system, the derivation of an associated 4D model, and its integration into CAD. The present system essentially takes expanded buccal scans at 8？Hz with sufficient data to define a local relative jaw position. Since 3D surface files are produced, they can be used to (1) derive incremental transforms to characterize the motion and (2) directly register the 3D oral anatomy of interest to be animated. 2. Imaging Method Fluorescent polystyrene microspheres (beads) of about 20？μm diameter are brushed onto the areas of the upper and the lower arches to be imaged, spanning about six teeth. These areas should lie within the oral anatomy of interest to be animated. Both hard and soft tissues can be imaged. The purpose of the beads is to produce a random high-contrast optical pattern to the imaging system. The beads are suspended in a viscous ethanol solution containing polyvinyl pyrrolidone and a colorant. After brushing on, the alcohol