DENTAL ALLOYS:
It is a combination of 2 or more metals obtained in a molten state, their properties change depending on their number and concentration.
2)-Classification: -According to the number of constituents: binary, ternary, quaternary. …..or complex.
-According to the miscibility of atoms in the solid state => the simplest alloy is that in which the atoms of two metals merge in the same spatial network, the metals are then said to be soluble in each other in the solid state (solid solution).
-According to their values:
-precious alloys:
-non-precious alloys.
3)- Qualities required of a Dental Alloy:
-Hard :
-Elastic;
-Break resistant:
-Easy to pour;
-Corrosion resistance;
-Inert in humoral fluids:
-Non-toxic;
-Well supported by soft tissues.
4)-Precious alloys:
The full range of products used for permanent prostheses ranges from yellow platinum-plated gold alloys to more or less heavily palladium-plated white golds.
4-1)-Composition: The percentage varies from one type to another depending on the carat and title. Carat (K) for gold and title for other metals.
-The carat of an alloy is the number of parts of pure gold in an alloy divided into 24 parts.
eg: 24 carat gold = fine (pure) gold;
22 carat gold = 22 parts gold + 02 other metals:
18 carat gold = 18 parts gold + 06 other metals (this is the most used in dentistry).
In general the different constituents are:
-Gold: yellow coloring and increases resistance
-Copper: increases strength and hardness;
-Silver: tends to whiten the alloy
-Platinum: hardener and strengthener
-Palladium same effect as platinum but it is cheaper
-Zinc: used in small amounts as a deoxidizer and increases fluidity.
4-2)-physical properties: Melting range = 870 to 960°C.
4-3)-Chemical properties: are more resistant to corrosion compared to non-precious alloys.
4-4)-Biological properties: the higher the concentration of noble metals, the more the alloy is well tolerated in the mouth.
Non-precious alloy: Cobalt-chromium alloy (Co-Cr)
*Composition :
The main constituents: -Co at 60% -Cr at 25 to 30% => resistance to corrosion.
Secondary constituents:
-Manganese (Mn) and silicon (Si) => increase fluidity
-Molybdenum (Mo), Tungsten (W) and Carbon (C) =>: reinforcers.
*Application in dentistry:
– Prosthetic plates (bases);
-Hooks (thread).
*Physical properties: – Tf: 1399°C to 1454°C.
*Chemical properties:
-Chlorine attacks alloys that contain chromium.
*Biological properties: -Problems are often due to poorly designed or poorly fitted prostheses.
Nickel chromium alloy (Ni, Cr):
Composition :
-Ni: 67 to 80%,
Cr: 12 to 20%;
-In addition Mo, Al, C, Mn and Si.
-Sometimes Beryllium in small quantities (0.2 to 0.5%) to lower the melting temperature.
*Application in dentistry:
-In fixed prosthesis: Crowns and bridges.
*Physical properties:
-Tf: 1232 to 1343 ° C.
*Chemical properties: -are less resistant to corrosion than gold alloys.
*Biological properties: – Beryllium can cause berylliosis (formation of granulomas on the lungs) when casting the alloy.
3)-Silver amalgams:
Composition: Silver (Ag): 65 to 74%
Tin (Sn): 24 to 29%
Copper (Cu): 00 to 06%
Mercury (HG): very pure is mixed with the alloy to produce a plastic mass which will harden from the setting reaction.
*Application in dentistry:
-Restoration of posterior teeth
-Repair of complete crown pillars .
DENTAL ALLOYS
Impacted wisdom teeth may require surgery.
Zirconia crowns are durable and aesthetic.
Bleeding gums may indicate periodontitis.
Invisible orthodontic treatments are gaining popularity.
Invisible orthodontic treatments are gaining popularity.
Modern dental fillings are both durable and discreet.
Interdental brushes are ideal for narrow spaces.
Good dental hygiene reduces the risk of cardiovascular disease.