Abstract
The development of digitized techniques for manufacturing implant frameworks has made possible alternative "impression" techniques for recording implant positions. The objective of the present study was to test the precision and accuracy of a three-dimensional photogrammetric technique to record implant positions in vitro and to compare casts made with this technique with conventional casts fabricated with two conventional impression techniques. Twenty casts were fabricated from 10 polyether (Impregum, ESPE Dental AG, Seefeld, Germany) impressions and 10 plaster (Kühns Abdrucksgips, Ernst Hirnischs GmbH, Goslar, Germany) impressions of one master model. The casts were measured in a coordinate measuring machine (Zeiss Prismo VAST, Oberkochen, Germany) and compared with the master model. Six separate three-dimensional photographs of the master model were taken with a special camera. After the photographs were measured with an analytic plotter, results were analyzed and compared to the coordinates of the original model and casts. A systematic pattern of distortion in the x-axis was found for the two impression techniques. Expansion of the implant arch at the terminal implants (p < .01) averaged 22 microm and 94 microm on photographs and plaster casts, respectively. Polyether casts contracted an average of 52 microm when compared with the master (p < .01). In absolute figures, photogrammetry and the polyether technique reproduced the x-axis and three-dimensional parameters more accurately than the plaster technique did when cylinder center point distortion was compared (p < .05 to p < .001). However, angular cylinder distortion in absolute figures was greater with the photographic technique than with either of the impression techniques (p < .05-p < .001). Photogrammetry is a valid option for recording implant positions and has a precision comparable to that of conventional impression techniques. At present, however, it is limited to framework fabrication techniques that are based on digital platforms.
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