Effect of reusing cobalt-chromium alloy powders in direct metal laser sintering on powder characteristics and metal-ceramic bond strength.

Abstract

The purpose of this in vitro study was to evaluate the effect of reusing Co-Cr alloy powders without addition of new powder on powder characteristics, ion release, and metal-ceramic bond strength. Co-Cr alloy powders consisting of virgin powder (G1) and powders reused through the 4th (G4), 7th (G7), 10th (G10), and 13th (G13) manufacturing cycles of a DMLS system were analyzed by scanning electron microscopy (SEM), laser particle size distribution (LPSD), and X-ray diffraction (XRD). Bar-shaped Co-Cr specimens (0.5 × 3 × 25 mm) were fabricated with DMLS from the corresponding powder groups (n = 15), veneered with porcelain according to ISO 9693-1, and tested for metal-ceramic bond strength using 3-point bending. Ion release was measured with inductively coupled plasma mass spectrometry (ICP-MS). Bond strength data was analyzed with 1-way analysis of variance and Dunnett T3 tests (α = .05), and Weibull analysis was performed for reliability assessment. No significant differences were found in metal-ceramic bond strength among the groups (P > .05). Mean bond strength values ranged from 56.8 ± 8.2 MPa (G7) to 78.2 ± 39.5 MPa (G13). SEM analyses revealed progressive powder deformation with increasing reuse cycles, whereas LPSD analysis demonstrated only slight changes in particle size distribution (d50: 23.4-23.7 μm). XRD analysis demonstrated similar cubic-phase characteristics among all groups. ICP-MS analysis demonstrated increased Co, Mo, and W ion release with increasing powder reuse, whereas Cr remained undetectable in all groups. Repeated reuse of Co-Cr alloy powders without virgin powder adding did not adversely affect metal-ceramic bond strength but resulted in progressive morphological deformation and increased ion release with increasing reuse cycles.