Untersuchung zur Genauigkeit verschiedener Abformmethoden in Kombination verschiedener Abformmaterialien bei Verwendung des Brånemark®-Implant-Systems

During the past 20 years, the oral intraosseous implantology has developed to a well-accepted treatment concept. The number of prosthetic restorations, partially or totally retained by osseointegrated dental implants, is steadily increasing. The maximum possible precision is needed in every step of fabrication of these sophisticated restorations, whereas impression-taking and fabrication of high-precision models are of utmost importance. Thus, the aim of this study was to investigate the accuracy of various techniques of impression-taking by using different impression materials, in combination with the Brånemark™-Implant-System. Both, impressions and casts have been investigated. On the basis of a virtual case, an acrylic master cast simulating an edentulous lower jaw was fabricated and provided with five Brånemark™ MK II Implants which were inserted parallel to each other. Impressions were taken by a device specially con-structed for this purpose. With this device, it was possible to take impressions un-der reproducible conditions and served as an aid in pouring the impressions as well. The following techniques and materials were investigated: 1. Indirect transfer coping technique (open tray) in combination with Monopren™ transfer using a single-phase, one-step impression technique and Provil™ P / M.C.D., using as well a single-step, putty-wash impression technique and a two-step putty-wash impression technique. 2. Direct transfer coping technique (closed tray) in combination with Impregum™, Baysilex™ C.D., Monopren™ transfer using a single-phase, one-step impression technique and Provil™ P / M.C.D using a single-step, putty-wash impression technique. For each of the seven above listed techniques, five impressions were taken and five casts were poured, reusing the transfer copings and implant analogues within one series of experiment. The distances between the implants were divided into 10 measuring sections and were measured on both impressions and casts, in the horizontal plane by using an electronic measuring projector TP 300 with an accuracy of ±7 microns. The single-phase, one-step impression materials produced the smallest deviations when used with the indirect transfer coping technique. The largest deviations occurred with Monopren™ and Provil™ (two-step putty-wash impression technique) used with the indirect transfer coping technique. Impressions and casts fabricated by the indirect transfer coping technique showed significantly smaller deviations to the master cast. The measurement of both impression and cast allowed an exact analysis of where the error occurred and made it possible to evaluate if the error produced during impression-taking was reproduced on the cast, or, if the error occurred independent from impression-taking. The subsequent correlation analysis showed a highly significant mean correlation for Impregum, direct transfer (r = 0,501***) and all indirect transfer combinations (r = 0,514*** – 0,634***). Furthermore, it was tested if reusing transfer copings and implant analogues impairs the accuracy of impressions and casts. The results indicate that reusing these components up to 4 times does not negatively affect the accuracy of both models and casts.