Image-based tracking of the teeth for orthodontic augmented reality.

We present image-based methods for tracking teeth in a video image with respect to a CT scan of the jaw, in order to enable a novel light-weight augmented reality (AR) system in orthodontistry. Its purpose is guided bracket placement in orthodontic correction. In this context, our goal is to determine the position of the patient maxilla and mandible in a video image solely based on a CT scan. This is suitable for image guidance through an overlay of the video image with the planned position of brackets in a monocular AR system. Our tracking algorithm addresses the contradicting requirements of robustness, accuracy and performance in two problem-specific formulations. First, we exploit a distance-based modulation of two iso-surfaces from the CT image to approximate the appearance of the gum line. Second, back-projection of previous video frames to an iso-surface is used to account for recently placed brackets. In combination, this novel algorithm allowed us to track several sequences of three patient videos of real procedures, despite difficult lighting conditions. Paired with a systematic evaluation, we were able to show practical feasibility of such a system.