Marginal and internal fit of metal-ceramic crowns fabricated with a new laser melting technology

OBJECTIVES: The purpose of this in vivo investigation was to evaluate the marginal and internal fit of metal-ceramic crowns fabricated with a new laser melting procedure (BEGO Medical, Bremen, Germany), and to investigate the influence of ceramic firing on the marginal and internal accuracy of these crowns. METHODS: After tooth preparation, impression taking using polyvinylsiloxane and model casting, each preparation was contact less scanned by strip-light-projection. The finishing line and the virtual construction of the metal coping were defined by means of a computer. Using CAD/CAM software the metal copings were produced by BEGO Medical (Germany). A base metal alloy (Wirobond C) and a precious alloy (BioPontoStar, both: BEGO Medical) were used in this study with 14 restorations each. The internal and marginal accuracy of the specimens were examined using a silicone indicator paste (Fit Checker, GC, Japan). After setting, the silicone films were embedded in acrylic resin and sectioned four times. Each slice was photographed digitally at 60x magnification for marginal and at 15x magnification for occlusal adaptation, respectively. Using a light microscope the thickness of the silicone layer was measured at 10 reference points, a total of 3360 measurements. This procedure was repeated after the ceramic firing in the dental laboratory and after intraoral adjustment clinically. RESULTS: No statistically significant differences between the two alloys were found at any time. The mean marginal discrepancies ranged from 74 to 99mum for both alloys. The internal gaps ranged from 250 to 350mum. Ceramic firing increased the marginal discrepancies while the internal gaps decreased especially at occlusal surface. However, only in one case a slight statistically significance could be determined (p=0.046). SIGNIFICANCE: The results of this in vivo study show that crowns produced with laser melting technology exhibit a marginal and internal accuracy that is comparable to conventional production procedures.