A voice-coil actuated ultrasound micro-scanner for intraoral high resolution impression taking

Silicone based impression-taking of prepared teeth followed by plaster casting is well-established but potentially less reliable, error-prone and inefficient for newly emerging techniques such as computer aided design and manufacturing (CAD/CAM) of dental prosthetics. Intra-oral optical scanners have been introduced to increase efficiency of CAM but no breakthrough occurred so far. Oral liquids such as saliva, blood and sulcular fluid are still one of the main problems since the preparation area must be completely dry. Moreover, sub-gingival preparations need to be uncovered invasively prior to scanning and a reflecting powder coating is required in some cases. High frequency ultrasound (HFUS) has been recently introduced as an alternative to optical scanning. Ultrasound is less sensitive against oral fluids and in principal able to penetrate gingiva in a patient-friendly and cost-effective way. Although HFUS systems have been introduced for ophthalmology, dermatology or small animal imaging, none of them suits the challenging requirements and high accuracy demands for intra-oral micro-scanning of prepared teeth. For this reason, we conceived a new ultrasonic micro-scanning device based on a voice-coil actuated spherically focused HFUS transducer for intra-oral use. The system, which is designed for both highly dynamic accurate positioning and micrometer-resolution, is supplied with a sensor providing position feedback for motion control as well as the ultrasound trigger engine. In this contribution, we describe the set-up and evaluate the lateral displacement of the micro-scanners end-effector with respect to the oscillation rate using laser triangulation. The results are in good agreement to the requirements of an intra-oral ultrasound based micro-scanner.