Chromium-cobalt-molybdenum alloy
The cobalt-chromium alloy belongs to the cobalt-based alloys . It is used in prosthetics , a branch of dentistry , to manufacture dentures . In technical jargon, it is often simply called an NEM alloy . Just as simplistic (and incorrectly) one speaks of a piece of steel in dental technology and means a model cast prosthesis .
composition
Depending on the manufacturer, the following values differ slightly:
- about 62-66% cobalt
- approx. 27-31% chromium
- approx. 4-5% molybdenum
In addition, the alloys contain in small amounts: carbon , silicon , manganese and iron .
properties
Physical Properties
- Density : approx. 8 g / cm³
- Melting temperature : approx. 1250 ° C to 1500 ° C (this requires a plaster-free investment material )
- Yield strength : approx. 630 N / mm²
- Tensile strength : approx. 890 N / mm²
- Elongation at break : approx. 10%
- Brinell hardness : approx. 365 kg / mm² (for comparison: pure gold: approx. 20 kg / mm², dental (dental) gold alloys: approx. 60–145 kg / mm²)
Advantageous properties for use in dentistry
- very fluid, so it enables the finest models to be poured
- enormous hardness
- enormous elasticity (twice as large as with precious metal alloys)
- large bridge spans possible
- completely corrosion-free
- no discoloration in the mouth due to influences such as saliva or food
- good soldering properties (important for prosthesis extensions)
-
physiological properties:
- When using " biomaterials " such as gold , platinum or titanium , the physiological advantage over conventional non-precious metal alloys is emphasized . However, in the case of gold in particular, economic aspects presumably take precedence over those of patient welfare. Titanium is to be regarded as historical in prosthetics; it is used almost exclusively, and here very successfully, for endosseous implants and their superstructures. Silver-palladium alloys containing platinum are suspected of causing allergies.
See also
literature
- Paul Weikart: Materials science for dentists , 4th edition, Carl Hanser Verlag, Munich
- Walter Hoffmann-Axthelm : Lexicon of Dentistry , Quintessenz-Verlag, Berlin