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1. INTRODUCTION2. CLASSIFICATION3. GOLD FOIL4. ELECTROLYTIC PRECIPITATE5. POWDER GOLD6. MANIPULATION OF DIRECT FILLING GOLD7. DESORBING OR DEGASSING8. COMPACTION9. ADVANTAGES & DISADVANTAGES
Pure gold can be used as an restorative material. Most noble metal, rarely tarnishes in oral cavity Cold welding property Applications 1. Pits and small class I restorations 2. For repair of casting margins 3. For Class II and Class V restorations 4. Repair of cement vent holes in gold crowns
Oldest Manufacture:A cast ingot of 15 mm thickness is beaten to a submicroscopic thickness of 15 or 25 µm Supplied as:FIat square sheets of varying thickness. No. 4 wt. 4 grains (0.259 gram) 0.51 µm thick. No. 3 wt. 3 grains (0.194 gram) 0.38 µm thick.
Preformed foils: Ropes & cylinders available in preformed shapes. Made from No. 4 foil that has been “carbonized” or “corrugated” Platinized Foil Pure platinum foil sandwiched b/w two sheets of pure gold Bonded by cladding process Increases hardness Available in No. 4 sheet form
Cohesive & Non-Cohesive Gold Cohesive: o For cold welding gold should have a clean surface o Gold attracts gases and any absorbed gas film prevents cohesion of individual increments of gold o Cohesive gold is supplied free of contaminants Non-Cohesive: o Gold is subjected to volatile agent such as ammonia, which is absorbed on surface o Acts as a protective film o Volatile film readily removed by heating o Rarely used nowadays
Crystalline gold powder is formed by electrolytic precipitation. Powder is formed into shapes by sintering(heat fusion). Available as: mat, mat foil & alloyed Mat gold: Crystalline Formed in strips Easy to build up the internal bulk, more easily compacted & adapted Results in pitted external surface, so covered with a veneer of foil gold Mat foil: Sandwich of electrolytic precipitated gold powder b/w sheets of No.3 gold foil
Done to eliminate the need to veneer the restoration with a layer of foil No longer marketed Alloyed Electrolytic Precipitate: Newest form is Electraloy RV Alloy of gold & calcium (0.1 to 0.5% by wt) Calcium produce stronger restoration by dispersion strengthening Alloy sandwiched b/w two layers of gold
Gold powder is enclosed in a No.3 gold foil Manufacture: Fine powder is formed by chemical precipitation or atomizing the metal Pellets mixed with soft wax, burned off later & wrapped in gold foil Available as: Foil acts as an effective container and matrix for the powdered metal Powdered gold pellet increases cohesion & reduces time required for placing it, because each pellet contain more metal by volume tan same sized pellet of gold foil Powdered gold pellets have cylindrical or irregular shape & diameter of 1 – 2mm Ratio of gold foil to powder varies from 1 to 3 for small pellets to 1 to 9 for largest
There are two process involved 1. Degassing 2. Compaction
During storage & packing of cohesive gold, they absorb gasses from atmosphere Prevents it from fusing Removed by heating- DEGASSING Heating done in two ways 1. In bulk on a tray, by gas-flame or electricity 2. Piece by piece, in a well adjusted alcohol flame Totally dry cavity needed to allow complete cohesion
The gold may be compacted by 1. Hand mallet 2. Pneumatic vibratory condenser 3. Electrically driven condensers
STRENGTH:- Greatest strength-most dense area Weakest part- porous area In DFG failure occurs from incomplete cohesion, thus transverse strength is a measure of cohesion HARDNESS Indicates overall quality Indicates presence of porosity DENSITY Density of pure gold is 19.3gm/cm ³ DFG density less than pure gold because it is not possible to eliminate voids completely during compaction
EFFECT OF VOIDS Amount of voids estimated by apparent density of compacted gold Voids on surface, increase susceptibility to corrosion and deposition of plaque Voids at the restoration-tooth interface cause gross leakage and secondary caries development TARNISH & CORROSION Resistance to tarnish and corrosion is good if compacted well BIOCOMPATIBILITY Pulpal response is minimal if compacted well This procedure causes a certain amount of trauma to the tooth and supporting structures Mechanical condensor causes less trauma than the manual technique
ADVANTAGES Tarnish and corrosion resistant Good mechanical properties Good biocompatibility DISADVANTAGES Poor esthetics High coefficient of thermal expansion Manipulation is difficult