[Abstract]
Objective
To investigate the effects of different printing orientations and heat treatment temperatures on the fit and hardness of cobalt-chromium (Co-Cr) crowns fabricated using selective laser melting (SLM) technology.
Methods
SLM Co-Cr crowns were printed at 0°, 45°, and 90° orientations and subjected to heat treatment at 750°C, 980°C, 1150°C, or none (n=10 per group). The silicone replica technique was used to assess marginal and internal gaps at 20 measurement points across five areas: occlusal, axial wall, axio-occlusal, cervical, and marginal gaps (MGs). Vickers hardness was assessed at the occlusal surface of crowns. Statistical analyses included two-way (α=0.05).
Results
Crowns printed at a 90° orientation exhibited significantly larger marginal and internal gaps than those printed at 0° or 45° orientation, regardless of heat treatment temperature (p<0.001). Occlusal region showed the largest discrepancies, while axial walls exhibited the smallest. Clinically acceptable MGs (<120 µm) were observed in crowns printed at a 0° orientation without heat treatment and at 0° or 45° with heat treatment at 1150°C. Crowns treated at 1150°C demonstrated the lowest hardness values, while those treated at 750°C or at 980°C showed significantly higher hardness but larger, clinically unacceptable MGs at certain locations (p<0.05).
Conclusions
Printing orientation and heat treatment significantly influenced both fit and hardness of SLM Co-Cr crowns. A 0° printing orientation without post-printing heat treatment, and 0° or 45° with heat treatment at 1150°C, are preferable for fabricating SLM Co-Cr crowns to achieve favorable fit and hardness.