Marginal evaluation of CAD/CAM generated crowns with different marginal angles

Objectives: The purpose of this study was to explore to what extend a CAD/CAM machine (CEREC system) can produce acute marginal angles creating restorations with clinical acceptable margins, in relation to three different restorative materials. Materials and Methods: For the purpose of this study three brass models were prepared with a different bevel finishing line, namely a 0° bevel (or 90° shoulders), a 30° bevel and a 60° bevel. A duplicate model of each brass model was scanned with the help of CEREC Scan^TM (Sirona). A crown restoration was designed using the Cerec3 software and three crowns were milled for each design using Paradigm MZ100^TM Blocks (3M/ESPE), Vitablocks Mark II (VITA) and ProCAD Blocks (Ivoclar-Vivadent). An image of the margins of each crown was taken and qualitative and quantitative analysis of the marginal integrity was performed with the aid of microscopy and image analysis. Results: The results of this study indicated that there were no signs of marginal chipping for the 0° bevel finishing line regardless of the restorative material used. Some signs of marginal chipping were detected in the 30° bevel group. The group of the 60° bevel had the poorest results. Also it was found that there was a relation to the material used, with the ProCAD showing the poorest margins and the Paradigm MZ100 showing margins with the fewest defects. Conclusions: When the Cerec system is used acute bevel finishing lines are not recommended due to chipping of the margins, which could impair the future clinical performance of the restoration. Acknowledgements: We are grateful to 3M/ESPE for the donation of the resin composite blocks and the impression materials and Ivoclar-Vivadent for the donation of ProCAD blocks.