1999 Volume 19 Issue 2 Pages 158-162
We have been developing a new system to fabricate crown restorations automatically by using a CAD/CAM process. The newly developed laser displacemeter was composed in the CAD/CAM device to digitize the surface of the stone model to obtain the morphological information of the abutment. Even a laser digitizer has merit to measure the object quickly, we afraid the accuracy of the digitizing, especially on the axial wall and the margin of the crown abutment. Therefore in this study, the digitizing accuracy of the stone model was investigated by using a simplified abutment model, which has a perpendicular axial wall and a shoulder margin with a different width. The developed laser digitizer could recognize both the axial wall and shoulder with a digitizing pith of 20 μm. However, since the sharp corner of the original model was recognized as a round corner, the width of the shoulder was recognized as being smaller than that of the original width. This discrepancy became smaller as the width of the shoulder enlarged. Furthermore, the digitized height of the shoulder was slightly elevated when the model was digitized along the medial-distal direction because of the secondary reflect of the irradiated laser beam on the stone model. These results suggest that the developed laser digitizer was useful, but we need more investigation on the digitizing conditions to increase the digitizing accuracy.
