High frequency (75MHz) ultrasound based tooth digitization using sparse spatial compounding

Over the last decade, extra- and intraoral optical scanning for computer integrated manufacturing (CIM) of dental restorations became the focus of interest. Despite the fact that intraoral systems are getting more and more accurate, their invivo accuracy is influenced by the presence of oral fluids. Moreover, subgingival preparation margins need to be uncovered invasively prior to the scan and powder may be required to cope with different translucency and reflectivity of target materials. High frequency ultrasound (HFUS) based intraoral micro-scanning could be an alternative technology for optical impression taking. However, for accurate 3D teeth geometry reconstruction, homogenously distributed echoes of the occlusal and lateral tooth surfaces as well as margins are required. Whereas HFUS phased array technology for 3D image compounding is not yet available, mechatronic single element based transceiver concepts at most require 5 degrees of freedom (4 in case of synthetic aperture focusing). To overcome these drawbacks, a sparse spatial compounding (SSC) technique is being investigated which makes use of only a limited number of additional scanning directions under a fixed incidence angle allowing for simplification of the final micro-scanning kinematic. Measurements with extracted prepared human molar teeth have been carried by using an extraoral HFUS-SSC scanner. The results demonstrate that with SSC almost homogenously distributed spatial data coverage of tooth surface points can be achieved.