Trueness of four different milling procedures used in dental CAD/CAM systems

Milling is a crucial step in producing restorations using computer-aided design and computer-aided manufacturing (CAD/CAM) systems. In this study the trueness of currently available milling devices was evaluated. Thirty clinical cases (ten inlays, ten crowns, ten onlays) were milled from ceramic blocks using four different milling approaches: five axis with IMES CORiTEC 450i, four axis with CEREC MCXL, four axis with CEREC MCXL-EF and five axis with inLab MCX5. The milled restorations were scanned and the occlusal and inner surfaces compared to the originally calculated 3D surface using difference analysis software. The (90-10 %) / 2 percentile of the distances were calculated and analysed using one-way ANOVA with the post hoc Scheff, test (alpha = 0.05). Chipping of marginal areas were visually examined and analysed using one-way ANOVA with a post hoc Tamhane test (alpha = 0.05). At inner surfaces, the milling trueness of IMES (33.9 +/- 16.3 mu m), X5 (32.3 +/- 9.7 mu m) and MCXL-EF (34.4 +/- 7.5 mu m) was significantly better (p < 0.001) than that of MCXL (62.1 +/- 17.1 mu m). At occlusal surfaces, MCXL-EF (25.7 +/- 9.3 mu m) showed significant higher accuracy (p < 0.001) than MCXL (48.7 +/- 23.3 mu m) and X5 (40.9 +/- 20.4 mu m). IMES produced the most chipping (p < 0.001). Five-axis milling devices yield high trueness. MCXL-EF is competitive and may allow chairside fabrication with good milling results. Accurate milling is required for well-fitting restorations and thereby requires fewer manual finishing steps, yields smaller marginal gaps, resistance to secondary caries and longevity of restorations.