Date of Award
Master of Science (MS)
Introduction: Many impressions sent to commercial laboratory dental technicians may include marginal defects. In order to fabricate accurate restorations, digital technology may be used to merge digital files of defective impressions into a single Standard Tesselation Language (STL) file, free of errors. Material and Methods: Ivorine teeth on a dentoform were prepared to receive a posterior fixed dental prosthesis (FDP). A flawless impression was made in a sectional tray using polyvinyl siloxane (PVS) impression material. An extraoral scanner was used to digitize the impression; this was the reference cast. Wax was used to create defects on the buccal and lingual margins of the preparations. Fifteen conventional sectional PVS impressions were made of the FDP preparations. After impressions were made, the wax was removed, and new defects were made on the mesial and distal margins of the preparations and an additional 15 conventional sectional PVS impressions were made in the same fashion. All impressions were digitized using the same extraoral scanner. For each pair of impressions, 2 STL files were created with the defects that had been incorporated on alternating preparation margin surfaces. The 2 STL files were then merged and a master cast was created by eliminating the defects using the scanned data. This master cast was compared to the reference cast using a reverse engineering software. Positive errors were counted as areas were the margins of the preparations on the master cast were raised in comparison to the reference cast, while negative errors were counted as areas were the margins of the preparations on the master cast were depressed in comparison to the reference cast. Statistical analysis was done using Microsoft Excel 2016 (Microsoft, WA, USA). Results: The mean average error in the sample was -0.4 μm. The average upper limit of 95% confidence interval was 36.5 μm, while the average lower limit of 95% confidence interval was -37.3 μm. The mean RMS of the errors found was 18.9 μm.Conclusions: Merging digitized definitive impressions to correct marginal defects resulted in master casts with high level of accuracy relative to the standard reference.