Comparison of the accuracy of fit of CAD/CAM crowns using three different data acquisition methods

Background. Earlier research evaluated the 3D internal fit of CAD/CAM crowns after direct versus indirect laser scanning. To date, no study has evaluated the marginal integrity of all-ceramic crowns milled with different type of scanning systems via different methods of scanning. The purpose of This study was conducted to assess the marginal integrity of all-ceramic crowns milled with the E4D CAD/CAM system (D4D, Richardson, Texas) using three different scanning methods of a prepared model (direct scanning and indirect scanning of a cast, and scanning of an impression material).;Methods. A metal die model of a prepared mandibular first molar was fabricated according to specifications for tooth preparation for the E4D CAD/CAM system. Fifty five all-ceramic crowns were milled using this system: 5 crowns were made from scanning of the metal die; 25 crowns were made from scanning of 5 PVS impressions of the metal die, with each impression scanned 5 times; and 25 crowns were made from scanning stone dies poured from the same previous 5 PVS impressions. Each stone die was scanned 5 times. An internal gap to provide space for cement was kept constant at 25 microns. Marginal integrity of the crowns was assessed using optical microscopy. Results. The overall mean marginal gap and standard deviation for crowns was 78.1&mgr;m (18.9) for scanning the metal dies, 148.9&mgr;m (25.4) for scanning impressions and 126.2&mgr;m (28.2) for scanning the stone casts. ANOVA revealed significant differences in marginal gap between the three different groups. Conclusions. The direct scanning of a metal die produced crowns with significantly smaller marginal gaps than the marginal gap seen from scanning a PVS impression or a stone cast (P<.05). Additionally, it was found that scanning PVS impressions or stone casts, produced crowns with unacceptable mean marginal gaps (over 120&mgr;m). It was also observed that difficulty of scanning PVS impressions and tracing the finish line lead to overhanging margins and larger marginal gaps for both crowns produced via that method.