Luthardt RG, Bornemann G, Lemelson S, Walter MH, Huls A.
An innovative method for evaluation of the 3-D internal fit of CAD/CAM crowns fabricated after direct optical versus indirect laser scan digitizing.
International journal of prosthodontics. 2004;17(6):680-5.
A procedure for 3-D analysis of the internal fit of fixed restorations has been developed. This study tested this method for investigating the fit of all-ceramic crowns.
MATERIALS AND METHODS:
Twelve data sets of a prepared maxillary canine were acquired by direct digitizing of the metal master die (CEREC 3 camera) and by digitizing gypsum dies after conventional impression taking (CEREC 3 scan), respectively. Using these data sets, 24 all-ceramic single crowns each were machined out of two glass-ceramics. The method is based on duplicated gypsum dies of the metal master, which were made for each crown. The space between the duplicate die and the internal surface of the respective crown was filled with a low-viscosity addition silicone. These silicone films (replicas) and their corresponding dies were digitized in the same measuring position. The internal fit was calculated and quantitatively and qualitatively analyzed.
The mean and maximum positive deviations were 348 microm and 986 microm (camera), respectively, and 294 microm and 830 microm (scan), respectively, for Vitablocs Mk II and 332 microm and 920 microm (camera), respectively, and 307 microm and 852 microm (scan), respectively, for ProCAD. For both systems, the deviations were highest at the edges. CEREC scan yielded significantly better internal fit accuracy compared to the CEREC camera.
Evaluation of the internal 3-D fit using the innovative method proved to be suitable. Indirect data acquisition using impression taking showed improved internal fit compared with the direct procedure. However, the differences between the data-acquisition techniques are small compared to their absolute values.