Comparative analysis of the surface properties and corrosion resistance of Co-Cr dental alloys fabricated by different methods

Assessment of mechanical properties and microstructure of Co-Cr dental alloys manufactured by casting, milling, and 3D printing

STATEMENT OF PROBLEM

The mechanical properties and microstructure of cobalt chromium (Co-Cr) alloys should be considered when choosing the best alloy for each clinical situation. More information is needed on the digital manufacturing methods of metals in dentistry, such as computer numerical control (CNC), and direct laser metal sintering (DMLS).

PURPOSE

The aim of this study was to investigate the effect of the 3 different Co-Cr manufacturing processes on the mechanical properties and microstructure of Co-Cr dental alloys.

MATERIAL AND METHODS

Dumbbell-shaped specimens (n=6) were fabricated using casting (CAST), CNC, and DMLS techniques. Tensile, 3-point bend, and microhardness testing were performed, and the microstructure evaluated through scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction analysis. The ANOVA test followed by post hoc Tukey tests were used for statistical analysis (α=.05).

RESULTS

DMLS showed the greatest values for 0.2% yield strength (908.0 ±13.1 MPa), tensile strength (1123.7 ±6.5 MPa), flexural strength (2273.0 ±43.2 MPa), and microhardness (438.2 ±44.9 HV), followed by CAST and CNC. No statistical differences were found for elongation between CNC and DMLS or DMLS and CAST (P>.05). No statistical differences were found in elastic modulus among all groups (P>.05). EDX revealed a slightly different chemical composition among the groups. XRD showed face-centered cubic as the dominant phase and a small amount of hexagonal close-packed structure in all groups. A peak of σ phase was identified in the CAST group.

CONCLUSIONS

The mechanical properties and microstructures of Co-Cr dental alloys were significantly influenced by the fabrication method used. DMLS and CNC milling produced better products that traditional methods, leading to the improved durability and reliability of dental prostheses. These advancements underscore the importance of selecting appropriate fabrication methods to optimize clinical outcomes and patient satisfaction.

Metal Ions Release from Welded Co-Cr Dental Alloys

Cobalt-chromium alloys (Co-Cr) are widely used in dentistry due to their excellent mechanical properties and corrosion resistance. Since prosthetic materials must be permanently stable in the oral cavity, it is very important to determine the release of ions from alloys in the oral cavity. In dentistry today, metals and alloys are mainly joined by laser and tungsten inert gas (TIG) welding. Therefore, in this work, the release of metal ions from six different Co-Cr alloys joined by these two welding methods was quantified to determine the effects of the welding method on an ion release. Static immersion tests, atomic absorption spectrometry and statistical analysis were performed for this purpose. The results showed that laser-welded alloys release a lower amount of metal ions compared to TIG-welded alloys.

In vitro study of surface properties and microbial adhesion of various dental polymers fabricated by different manufacturing techniques after thermocycling

OBJECTIVES

The study aims to investigate surface properties and microbial adhesion of various dental polymers fabricated by different manufacturing techniques before and after thermocycling.

MATERIALS AND METHODS

The following six materials were used to fabricate disk-shaped specimens: conventional denture polymer (Vertex Acrylic Resin, VAR), CAD/CAM denture polymer (Organic PMMA eco Pink, OP), conventional temporary polymer (Protemp™ 4, PT), CAD/CAM temporary polymer (Die Material, DM), conventional denture framework polymer (BioHPP, PB), and CAD/CAM denture framework polymer (breCAM.BioHPP, CB). The specimens were tested before and after thermocycling (5000 and 10,000 cycles, 5 °C/55 °C). Surface roughness (SR), hydrophobicity, and surface topography were determined by profilometry, water contact angle, and scanning electron microscopy (SEM). Then specimens were incubated with Staphylococcus aureus, Streptococcus mutans, and Candida albicans for 24 h, respectively. Microbial adhesion was assessed using colony-forming unit counts, XTT assay, and SEM.

RESULTS

SR and hydrophobicity of VAR group were higher than that of OP group. S. aureus and C. albicans adhesion on VAR and PT groups were higher than that on OP and DM groups, respectively. There was no difference in surface properties and microbial adhesion between PB and CB groups. After thermocycling, SR (expect OP group) of all materials increased and hydrophobicity decreased, and the amount and activity of S. aureus and C. albicans adhesion also increased. The adhesion of S. aureus and C. albicans showed a moderate positive correlation with SR, independent of hydrophobicity.

CONCLUSIONS

CAD/CAM denture polymers and temporary polymers showed less S. aureus and C. albicans adhesion when compared to conventional ones, which were mainly affected by surface roughness, independent of hydrophobicity. Thermocycling could increase surface roughness, decrease hydrophobicity, and affect microbial adhesion of the materials.

CLINICAL SIGNIFICANCE

CAD/CAM dental polymers may be a better choice for the manufacture of temporary restorations and dentures to reduce microbial adhesion.