The microstructures and mechanical properties of cobalt-chromium (Co-Cr) alloys produced by three CAD/CAM-based processing techniques were investigated in comparison with those produced by the traditional casting technique. Four groups of disc- (microstructures) or dumbbell- (mechanical properties) specimens made of Co-Cr alloys were prepared using casting (CS), milling (ML), selective laser melting (SLM), and milling/post-sintering (ML/PS). For each technique, the corresponding commercial alloy material was used. The microstructures of the specimens were evaluated via X-ray diffractometry, optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy, and electron backscattered diffraction pattern analysis. The mechanical properties were evaluated using a tensile test according to ISO 22674 (n = 6). The microstructure of the alloys was strongly influenced by the manufacturing processes. Overall, the SLM group showed superior mechanical properties, the ML/PS group being nearly comparable. The mechanical properties of the ML group were inferior to those of the CS group. The microstructures and mechanical properties of Co-Cr alloys were greatly dependent on the manufacturing technique as well as the chemical composition. The SLM and ML/PS techniques may be considered promising alternatives to the Co-Cr alloy casting process.

Selective laser melting (SLM), used to fabricate metallic objects with high geometrical complexity, is currently of increasing interest to the fields of medicine and dentistry. SLM-fabricated products should have highly smooth surfaces to minimize the use of post-processing procedures such as finishing and polishing. This study investigated the effect of various laser process parameters (laser power, scan rate, and scan-line spacing) on the surface roughness of a Co–Cr dental alloy that was three-dimensionally (3D) constructed via SLM. Initially, a single-line formation test was used to determine the optimal laser power (200 W) and scan rate (128.6 mm/s) that resulted in beads with an optimal profile. During subsequent multi-layer formation tests, the 3D Co–Cr body with the smoothest surface was produced using a scan-line spacing of 100 μm. The findings of this study show that laser process parameters have crucial effects on the surface quality of SLM-fabricated Co–Cr dental alloys.

The influence of residual stress induced by sandblasting the zirconia ceramic surface on the resin bonding to the ceramic is still unclear. The effect of four different sandblasting conditions (with 50 and 110 μm alumina at pressures of 0.2 and 0.4 MPa) on the bonding of adhesive resin cement (Panavia F 2.0) to zirconia (Cercon^® ht) was investigated in terms of residual stress. The surface roughness and water contact angle of the zirconia surfaces were measured. The tetragonal-to-monoclinic (t–m) phase transformation and residual stresses (sin²ψ method) were studied by X-ray diffraction. The resin-bonded zirconia specimens were subjected to shear bond strength (SBS) tests before and after thermocycling (10,000 and 30,000 cycles) (n = 10). As the particle size and pressure increased, the roughness gradually and significantly increased (p = 0.023). However, there were no significant differences in roughness-corrected contact angle among all the sandblasted groups (p > 0.05). As the particle size and pressure increased, the m-phase/(t-phase + m-phase) ratios and compressive residual stresses gradually increased. After thermocycling, there were no significant differences in SBS among the sandblasted zirconia groups (p > 0.05). In conclusion, increased surface roughness and residual stress do not directly affect the resin bonding durability.

The present study comprehensively compared the microstructure, flexural strength, and fracture toughness of zirconia ceramics prepared via two different methods, subtractive milling (SM) and stereolithography (SLA). Disc- or rectangular-shaped zirconia specimens (Prettau (SM) and 3DMix Zirconia (SLA)) were prepared following each manufacturer’s instructions and polished. The microstructures of the two different zirconia specimens were studied by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, and electron backscattered diffractometry. The flexural strength and fracture toughness based on the indentation fracture method were measured for the two different zirconia ceramics. A greater number of small pores and smaller grains were found in the SLA specimen than in the SM specimen. The crystal structure and microstructure analysis revealed that both ceramics had a similar phase composition to each other. No significant differences in flexural strength (p = 0.242) or fracture toughness (p = 0.101) were detected between the two ceramics. The mean flexural strength of the SLA-fabricated zirconia as well as the SM zirconia satisfied the class 5 criteria (>800 MPa) in the ISO 6872 standard.

This in vitro study investigated whether different storage conditions of plasma-treated zirconia specimens affect the shear bond strength of veneering porcelain. Zirconia plates were treated with a non-thermal atmospheric argon plasma (200 W, 600 s). Porcelain veneering (2.38 mm in diameter) was performed immediately (P-I) or after 24 h storage in water (P-W) or air (P-A) on the treated surfaces (n = 10). Untreated plates were used as the control. Each group was further divided into two subgroups according to the application of a ceramic liner. All veneered specimens underwent a shear bond strength (SBS) test. In the X-ray photoelectron spectroscopy (XPS) analysis, the oxygen/carbon ratios of the plasma-treated groups increased in comparison with those of the control group. When a liner was not used, the three plasma-treated groups showed significantly higher SBS values than the control group (p < 0.001), although group P-A exhibited a significantly lower value than the other two groups (p < 0.05). The liner application negatively affected bonding in groups P-I and P-W (p < 0.05). When the veneering step was delayed after plasma treatment of zirconia, storage of the specimens in water was effective in maintaining the cleaned surfaces for optimal bonding with the veneering porcelain.

Titanium nitride (TiN) was deposited on the surface of a cobalt–chromium (Co–Cr) alloy by a hot-wall type chemical vapor deposition (CVD) reactor at 850 °C, and the coating characteristics were compared with those of a physical vapor deposition (PVD) TiN coating deposited on the same alloy at 450 °C. Neither coating showed any reactions at the interface. The face-centered cubic (fcc) structure of the alloy was changed into a hexagonal close-packed (hcp) phase, and recrystallization occurred over at 10 μm of depth from the surface after CVD coating. Characteristic precipitates were also generated incrementally depending on the depth, unlike the precipitates in the matrix of the as-cast alloy. On the other hand, the microstructure and phase of the PVD-coated alloy did not change. Depth-dependent nano-hardness measurements showed a greater increase in hardness in the recrystallization zone of the CVD-coated alloy than in the bulk center of the alloy. The CVD coating showed superior adhesion to the PVD coating in the progressive scratch test. The as-cast, PVD-coated, and CVD-coated alloys all showed negative cytotoxicity. Within the limitations of this study, CVD TiN coating to biomedical Co–Cr alloy may be considered a promising alternative to PVD technique.