DEFINITION“Chemical substance that is a good electrical and thermal conductor, when is polished is a good reflector “
FEATURES SHINE RESISTANCE TO CORROSION THERMAL AND ELECTRICALCONDUCTOR STRENGTH AND RIGIDITY DRIVE RESISTANCE
ALLOY : This are unions of 2 or more metallic elements.
In Dentistry, alloys are use except for:• pure gold laminated• commercial pure titanium• Silver points for endodontic
CHANGES IN THE METAL STRUCTURE lackluster : Loss of gloss or sheen in a alloy or metal surface. Pigmentation : Partial impariment on metal surface, or color change. CORROSION : Actual deterioration on metal surface.
• FACTORS CAUSING CORROSION– pH of the saliva.– Wrong adapted prosthesis.– Poor dental position.– Deposits of food.– Poor hygiene.– Food that release certain chemical components.– Drugs.– Fluctuations in temperature.
ALLOYS USED IN DENTISTRY Highly noble alloys (precious) Alloys of noble metals Predominantly base alloys
PRECIOUS METALSCorrosion resistance in the oral cavity:Gold, Platinum, Palladium, Rhodium,Ruthenium, Iridium, Osmium and Silver.There are four main metals: Gold,Palladium, Platinum and Silver.
Cast Metal Or DrainProcess for the constuction of a restoration or appliance out for the previously made a mouth waxed or pattern.
CAST ALLOYS FOR HIGHLY NOBLEComposition:2. Gold: malleability, resistance to corrosion.3. Silver: Hardness4. Zinc: decreases T fusion5. Platinum or Palladium: Hardness6. Copper: resistance and bactericidalNota: the white gold casting whit less gold and copper are not.
TIPOS DE OROS PARA COLADOSType I (SOFT GOLD)For the construction of scale in class III y V Type II (MEDIUM GOLD)For all types of deposits, plus ¾ cr owns and complete Type III (HARD GOLD)For small fixed bridges and removable Type IV ( GOLD EXTRA HARD)For large fixed bridges and removable palatal bars and lingual
NOBLE METAL ALLOYS (Semiprecious) 25% of noble metals, does not require gold: Silver - Palladium Palladium - Silver Silver - Tin
Developed as an alternative to those based on gold. There are two varieties: Silver 60-70% Palladium 25-30% Note: Some containe 10% copper. Palladium 60% Silver 30% Note: El 10% of other metals to failitate bonding with porcelain.
CHEMICAL PROPERTIES Pigmentation and resistance to corrosion properly handled. Note: It is possible to achieve adequate accuracy casting and a good polishing and acceptable welds.
DISADVANTAGES Fragile marginal edges Pigmentation Can not be welded Slight corrosion resistance After a short clinical use and even before cemented in the mouth have lost shine and later changed to dark
BASE METALS These are noble elements. Is the so called because it reacts with the environment and are use to protect an alloy against corrosion by passivity.
Welds WELDING : Intermediate element that is used to join metallic surfaces each other. It’s a technique for join 2Or more metal elements,Rebuild or repair a metal surface.
REQUIREMENTS Free toxic substance Resistant Flow Similar color Lower temperature of• fusion Corrosion resitant
TECNICAS PARA SOLDARTECHNICAL COMM : Requires the useof an intermediate (welding).WELD TECHNICAL : Application of heatto melt the two metal surfaces.ELECTRICAL TECHNICAL : Applicationof electric current-tap to join metallicsurfaces.
FLUX Facilitate the flow of welding,Eliminating impurities. They come in powder and paste Composition of flux for alloys with chromium :pottasium fluoride, boric acid, borax glass, and sodium carbonate or silica. And for gold alloys: Borax powder, boric acid and silica.