The trueness of CAD-CAM custom-milled post-and-cores: a comparison of three materials and two milling systems

The purpose of this in-vitro study was to evaluate the 3D digital trueness of CAD/CAM custom milled post-and-cores fabricated from three contemporary materials using two different 5-axis milling machines.

A standardized virtual post-and-core CAD design, augmented with landmarks for the standardization of milling, scanning, and 3D analysis protocols, was imported into the CAM software of two different 5-axis milling machines: the CORiTEC 350i and the InLab MC X5. Custom post-and-cores were fabricated from three distinct materials: zirconia, fiber-glass composite, and polyetheretherketone (PEEK). For each material, 10 post-and-cores were milled on each machine, resulting in a total of 60 custom samples. After milling, these post-and-cores were scanned using a standardized method. The resulting scan meshes were superimposed onto the reference CAD design mesh to evaluate 3D surface deviations. A two-way analysis of variance (ANOVA) was employed to determine the effects of material and milling machine on the trueness of the milled post-and-cores.

No significant interaction between material and milling machine was found (p=0.813). PEEK showed significantly lower deviations (mean of 37.2 μm) compared to zirconia (57.2 μm, p<0.001) and glass-fiber composite (48.8 μm, p=0.017). The 350i produced PEEK post-and-cores with mean deviations of 12.7 μm less than the MC X5 (p=0.03), with no significant differences for other material-machine combinations.

Both milling machines demonstrated high trueness in milling post-and-cores. PEEK outperformed zirconia in trueness. When milled with the CORiTEC 350i, PEEK showed a small improvement in trueness over glass-fiber; however, no significant difference was observed with the InLab MC X5. The CORiTEC 350i excelled in milling PEEK, achieving the least 3D deviation, highlighting the influence of both material and machine on the trueness of milled post-and-cores.