Purpose: The purpose of this study was to assess precision of crown prostheses that were fabricated by using 2 kinds of bur or 3 kinds of bur. Methods: The crowns were fabricated by using the first molar of the right maxillary in this study. The abutments that were prepared were scanned by using a scanner and designed by using CAD software. Based on the crown design, NC data were created with CAM software. The created NC data were used while fabricating the crown prostheses by using 5-axis milling machine. Scanning was done for the internal and external surface of the completed crown prostheses and 3-dimensional measurement was conducted for precision assessment. Results: The $RMS{pm}SD$ value for the external surface of the crown prostheses that was fabricated by using two burs and three burs were $28.5{pm}4.1{mu}m$ and $19.1{pm}2.8{mu}m$, respectively; and the value for two burs were bigger than that for three burs with statistical significance (p<0.001). The $RMS{pm}SD$ value for the internal surface of the crown prostheses that was fabricated by using two burs and three burs were $14.9{pm}1.9{mu}m$ and $13.3{pm}2.5{mu}m$, respectively; and the value for two burs were bigger than that for three burs but with no statistical significance. Conclusion: Based on this study, the prostheses that were fabricated by using 3 bur presented better stability compared to those that were fabricated by using 2 bur and statistically significant difference was found only in the external surface.

Keywords: Dental CAD/CAM systems,Milling bur,Milling machine,Precision,Three-dimensional evaluation,5-axis milling,