Construction and testing of a computer-based intraoral laser scanner for determining tooth positions

An optical set-up for intraoral data acquisition based on the principle of laser triangulation was developed. The system consists of a pig-tailed lase r with line generating optics, a stepping motor driven positioning stage, a commercial CCD (charge coupled device) camera system with frame grabber in terface, a control personal computer and a mirror system compensating for t he fact that there is no possibility of watching an object directly in the mouth under a certain angle except from a facial position during intraoral scanning. Due to the size of the prototype measurements were still restrict ed to plaster casts. In order to evaluate its accuracy, the measurements we re compared with those taken with a commercial laser scanner and a coordina te measurement table. The accuracy of the prototype scanner was determined to be Delta XYZ=0.04 mm using gauge blocks of given dimensions and proved t o range between the commercial laser scanner and the coordinate measurement table (i.e., it was slightly better than that of the commercial scanner). Applications in orthodontics were demonstrated by scanning plaster casts an d measuring distances on reconstructed surfaces. The measured distances sho wed a maximum deviation of about +/-0.2 mm compared with the data of the co ordinate measurement table, which served as a reference. In addition, recon struction of three-dimensional tooth movements was performed on the scan da ta. The translational and rotational parameters gained from the superimposi tion of scanned point clouds and describing tooth movement were also in goo d accordance with the reference. The achieved accuracy proved to be suffici ent for further development which should include a reduction in size and th e use of more precise device components. (C) 2001 IPEM. Published by Elsevi er Science Ltd. All rights reserved.