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SAS 16
| Question | Answer |
|---|---|
| ALLOY (DEFINITION) | a metal made by combining two or more metallic elements, especially to give greater strength or resistance to corrosion. |
| TWO GROUPS OF METALS: | Noble Metals Base Metals |
| NOBLE METALS (DEFINE) | a metal (e.g., gold, silver, or platinum) that resists chemical action, does not corrode, and is not easily attacked by acids. |
| GOLD: used in either pure form or in alloy because of its (4) | 1. excellent resistance to corrosion 2. good malleability 3. yellow color 4. has low melting point |
| the gold content can be described | carat or karat or fineness, or in percentage. |
| PALLADIUM (3) | 1. resistant to Corrosion 2. higher melting point 3. harder than gold |
| PALLADIUM (OTHER 2 STATEMENTS) | -used as HARDENER in gold-based alloy and white in color - if 90% of gold will be mixed with 10% of palladium, white gold will be produced. |
| PLATINUM (3) | 1. has very high melting point 2. harder than palladium 3. occasionally used because it does not mix to gold |
| BASE METAL (2) | any of certain common metals such as copper, lead, zinc and tin is a common and inexpensive metal |
| has reddish color and significantly hardens gold-based alloy | COPPER |
| also a useful hardener | SILVER |
| low melting element, used to prevent oxidation of the alloy during the casting process. | ZINC |
| OTHER BASE METALS (4-9) | 4. Nickel 5. Cobalt 6. Titanium 7. Iron 8. Tin 9. Indium |
| basic structure of metal or alloy. | Grains or Crystals |
| Grains or Crystals (2) | The smaller the grain of crystal the better will be the physical property of an alloy. To reduce the size of the grains or crystals GRAIN REFINER may be used |
| GRAIN REFINER | 1. Iridium 2. Ruthenium |
| Grain Boundaries (DEFINE) | – lines between crystals, usually made of an amorphous material |
| HEAT TREATMENT (DEFINE) | Reheating of alloys may change its physical properties, by changing the grain structure and crystal structure of the alloy. |
| EFFECTS OF HEAT TREATMENT IN NOBLE ALLOY | like Gold-based alloy with sufficient copper hardener, will usually improve its properties. |
| EFFECTS OF HEAT TREATMENT IN Base metal alloys | deteriorates the properties of the alloy |
| IMPORTANT PROPERTIES OF ALLOYS(4) | 1. Melting Range 2. Density 3. Strength 4. Hardness |
| do not melt at a specific temperature | Melting Range: |
| An alloy has a melting range of | 950-1000C |
| At 950 | some metal will be liquid |
| At 975 | almost all metals will be liquid |
| At 1000 | all metals in an alloy will be liquid |
| the temperature at which all of the alloy LIQUEFIES upon heating | Liquidus |
| the temperature at which all of the alloy SOLIDIFIES. important in soldering process and for porcelain bonded alloys | Solidus |
| Density (2) | – the amount of mass in grams that occupies a volume of 1 cubic centimeter. - in casting, high density alloy is easier to cast because the gravity can accelerate the molten metal more easily into the casting mold. |
| Strength | to resist any permanent change in shape, an alloy should possess enough strength |
| Hardness | the ability of a material to resist surface abrasion and indentation. |
| HARDNESS (2) | an alloy with high strength will have high hardness and will be difficult to polish - BASE METAL ALLOYS are generally the hardest of the alloy, even harder than enamel. |
| COMMON CASTING ALLOYS (ADA) | 1. High Noble Alloys 2. Noble Alloys 3. Predominately Base Metal Alloys |
| HIGH NOBLE ALLOYS (4) | REFER SAS |
| Noble Alloys (define) | have at least 25% noble metal content, but there is no stipulation of gold content. |
| GOLD BASED ALLOY | 40% gold and higher amounts of silver or copper compared to high noble alloy |
| PALLADIUM BASED ALLOY | 77% palladium, almost no gold, contains copper or gallium. |
| SILVER BASED ALLOY (4) | = 25% palladium = moderate density 10-12 g/cm3 = hardness and strength is equal or greater than high noble alloy = corrosion resistance – equal or lesser than high noble alloy = used in crown and bridge with or without porcelain covering |
| Predominately Base Metal Alloys (9) | CHECK SAS |
| COMPOSITION OF PREDOMINANTLY BASE METAL ALLOYS | CHROMIUM (Cr) COBALT (Co) NICKEL (Ni) |
| COMPOSITION OF PREDOMINANTLY BASE METAL ALLOYS | makes up 85-90% of the weight but limited effect onphysical properties |
| Chromium Cr (2) | = responsible for tarnish and corrosion resistance because of passivating effect. = its content to an alloy should not be more than 28-30%, because in excess, it only makes an alloy brittle |
| Co and Ni increases the | = modulus of elasticity = Strength = hardness and = fusion temperature up to certain percentage. = Co – 20-35%; Ni – 10-30% |
| ALLOYING ELEMENTS (10) | CHECK SAS |
| can cause allergic reaction, because 8%-15% of the population is allergic to nickel. | NICKEL |
| BIOCOMPATIBILITY OF ALLOY (3) | CHECK SAS |
| release less mass into the mouth | High-noble alloys |
| often release more alloys, that release of higher amount of metals into the mouth pose the biggest risk for unwanted reactions. | Predominantly base-metal alloy often |
| WROUGHT ALLOYS (5) | CHECK SAS |
| USES OF WROUGHT ALLOY (3) | 1. ORTHODONTIC WIRES 2. ENDODONTIC FILES 3. CLASP IN RPD |
| formed from predominantly base metal alloys | Orthodontic wires |
| Example OF ORTHODONTIC WIRES | Stainless steel Nickel-titanium ( Nitinol ) Cobalt-chromium Nickel ( Elgiloy) |
| may be stainless steel or Niti | Endodontic files |
| High noble wrought alloy, like “PGP” wires for platinum-gold palladium | Clasp in RPD |
| It will be soldered in casted framework. Since excessive heat can degrade the properties of wrought alloys, the soldering must be done carefully so that the fibrous grain structure of the wire is preserved. | Clasp in RPD |
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