Direct filling gold

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  • 1. BY,SMIJAL GM
  • 2. 1. INTRODUCTION2. CLASSIFICATION3. GOLD FOIL4. ELECTROLYTIC PRECIPITATE5. POWDER GOLD6. MANIPULATION OF DIRECT FILLING GOLD7. DESORBING OR DEGASSING8. COMPACTION9. ADVANTAGES & DISADVANTAGES
  • 3.  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
  • 4.  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.
  • 5.  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
  • 6.  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
  • 7.  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
  • 8.  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
  • 9.  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
  • 10.  There are two process involved 1. Degassing 2. Compaction
  • 11.  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
  • 12.  The gold may be compacted by 1. Hand mallet 2. Pneumatic vibratory condenser 3. Electrically driven condensers
  • 13.  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
  • 14.  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
  • 15.  ADVANTAGES  Tarnish and corrosion resistant  Good mechanical properties  Good biocompatibility DISADVANTAGES  Poor esthetics  High coefficient of thermal expansion  Manipulation is difficult