When a dentist determines that a patient's tooth cannot be saved and a dental crown or dental bridge is necessary, a time-consuming treatment marathon ensues. The dentist first has to make a silicone impression. The patient is sent home with a provisional repair while dental technicians model a plaster impression, which is scanned using digital cameras. From the geometric measurement data the matching dental prosthesis is produced.
Thanks to a new system developed by Fraunhofer Institute scientists, though, this intricate and laborious process could soon be a thing of the past. Their 3-D digitizer will provide the teeth contours--without a plaster model. "The three-dimensional coordinates of the tooth surface can be determined on the basis of measurements taken in the patient's mouth," says Dr. Peter Kühmstedt, group manager for 3-D measurement technology at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF (Jena, Germany).
Under a contract from German dental company Hint-Els, the Fraunhofer team developed an optical digitization system that scans the oral cavity and captures three-dimensional data of the teeth using camera optics. A complete picture of the individual tooth is created from several data records. After an all-round measurement, it is even possible to represent the complete jaw arch as a virtual computer image.
The measurement conditions in the confined oral cavity are challenging--so to obtain precise results, the scientists use fringe projections in which a projector shines strips of light on the tooth area to be measured. From the phase-shifted images the evaluation software determines the geometric contour data of the tooth. Two camera optics provide the sensor chip with image information from different measurement perspectives.
After the pixel-precise comparison of various camera images, the evaluation program recognizes any image faults and removes them from the complete image.
Because it is problematic if the patient moves while the images are being taken, .the scientists have made sure that the process takes place quickly. "The image sequence for each measurement position is captured in less than 200 milliseconds," explains Kühmstedt.
