DIRECT FILLING GOLD

CONTENTS1. INTRODUCTION2. CLASSIFICATION3. GOLD FOIL4. ELECTROLYTIC PRECIPITATE5. POWDER GOLD6. MANIPULATION OF DIRECT FILLING GOLD7. DESORBING OR DEGASSING8. COMPACTION9. ADVANTAGES & DISADVANTAGES

INTRODUCTION 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 restorations2. For repair of casting margins3. For Class II and Class V restorations4. Repair of cement vent holes in gold crowns

CLASSIFICATIONSHEET

COHESIVE

NON-COHESIVE

ROPES

CYLINDERS

LAMINATED

PLATINIZED

ELECTROLYTIC PRECIPITATE (mat gold)MAT

MAT FOIL

ALLOYED

POWDER

GOLD FOIL 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 surfaceo Acts as a protective filmo Volatile film readily removed by heatingo Rarely used nowadays

ELECTROLYTIC PRECIPITATE 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

POWDER 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

MANIPULATION OF DIRECT FILLING GOLD There are two process involved

1. Degassing 2. Compaction

DESORBING OR DEGASSING 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 electricity2. Piece by piece, in a well adjusted alcohol flame

Totally dry cavity needed to allow complete cohesion

COMPACTION The gold may be compacted by

1. Hand mallet2. Pneumatic vibratory condenser3. Electrically driven condensers

PROPERTIES OF COMPACTED GOLD 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/cm³ 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 & DISADVANTAGES

ADVANTAGES Tarnish and corrosion resistant Good mechanical properties Good biocompatibility

DISADVANTAGES Poor esthetics High coefficient of thermal expansion Manipulation is difficult

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