Gold

1. Gold DIRECT FILLING

2. Why gold??? • Pure gold is the noblest of all dental metal • Rarely tarnish or corrode in the oral cavity • Inactive chemically – is not affected by air, heat, moisture, or most of the solvent. • Highly durable, if proper case selection , cavity preparation and careful manipulation is done. • Direct filling gold restorations exhibit excellent marginal integrity and biocompatibility in the oral cavity. • Highest ductility & malleability – can be beaten into a very thin foil of submicron thickness

3. CLASSIFICATION of DFG 1. According to the microstructure • Hammered sheet (foils) • Electrolytic precipitated • Granulated gold (Encapsulate gold powder)

4. Hammered sheet (foils) • Foil (no- 3,4,5) • Laminated foil • Preformed – rope, cylinders • Carbonised –corrugated • Cohesive, non cohesive • Platinised • Mat foil

5. II. Electrolytic precipitated • Mat gold (sintered –strips – crystalline, spongy) • Mat – foil gold • Electralloy – Ca-alloy-strips

6. III. Granulated gold(Encapsulate gold powder) • Golden or EZ gold • Stop foil gold

7. 2. According to the surface condition • Cohesive (clean) • Non cohesive (containing adsorbed gas )

8. 3. According to the geometric form • Sheets • Ropes • Strips • Pellets • Cylinders

9. DFG supplied in 3 basic forms • Several forms of DFG are available for restorative purposes. All of them are cohesive and 99.99% pure (except platinized foil & alloyed electrolytic precipitate). • Foil ( fibrous gold) • Electrolytic precipitate ( crystalline gold) • Granulated gold (powdered gold)

10. Manufacturing methods of DFG

11. Gold Foil (fibrous gold) • Robert Woffendale 1795 • Also called as fibrous gold. • Provided in low thickness 0.6 µm • Very thin gold sheet are placed in between some special layer or Chamois leather, as alternative layer to form a ‘cutch’ & subjected to continuous hammering , until extremely thin foil is obtained • Then cut into small square pieces of 10X10 cm • Treated with ammonia gas (non cohesive form) • Placed alternatively in between the sheet of book & supplied to the dentist

12. No. 3 foil--- weighs 3 grains ( 0.194 grams) & thickness 0.38 microns • Standard no. 4 gold foil is supplied in 100 x 100 mm ( 4x 4 inch ) sheets that weighs 4 grains ( 0.259 grams) & thickness 0.51 microns. • No – 20 (20 grains), 40(40 grains), 60(60grains), 90(90 grains) foils are also available • Numbering system refers to the weight of the standard sheet

13. Sub –types of gold foil A. Sheet gold 1. Cohesive 2. Non- cohesive B. Ropes C. Cylinders D. Laminated foil E. Platinized foil F. Carbonized or Corrugated foil G. Mat –foil gold

14. A. Cohesive & non cohesive gold • Sheet gold foil can be supplied in both cohesive & non-cohesive condition • Cohesive Gold (pure form) :- • Gold attract gases eg. Oxygen, to its surface and any adsorbed gas film prevents cohesion of individual increments of gold, during their compaction. • Manufacturer therefore supplies the gold essentially free of surface contaminants, and thus inherently cohesive. This type of gold is known as cohesive gold.

15. Non – cohesive gold- • Manufacturer can subject the foil to ammonia gas, which is adsorbed on surface of gold, acts as a protective film. • Minimizes adsorption of other less volatile substance & prevents premature cohesion of sheet that may come into contact • This ammonia treated foil is called as non – cohesive gold. • Before the use volatile film should be removed by a process known as desorption (Because for cold – welding procedure gold should have a clean surface free from impurities.)

16. B. Gold foil Ropes • 10 cm square piece of No-4 Gold foil is cut into ¼, 1/8, 1/16 small pieces & rolled into ropes mechanically.

17. C. Gold foil cylinders Produced by rolling cut segments of No.4 foil into desired width 3.2 mm 4.8 mm 6.4 mm etc size & then supplied

18. D. Laminated gold foil • Prepared in clinics. • By placing few foils one over the other . • Then cut into pieces to facilitate condensation .

19. E. Platinized gold foil • Objective of adding platinum: • Increases hardness and wear resistance • It is a laminated structure ,can be produced in one of the 2 ways. 1. Two sheets of no. 4 pure gold foil and a layer of pure platinum foil sandwiched between them, can be hammered until the thickness of no. 4 foil is achieved. or 2. Layers of platinum and gold sheet can be bonded together by cladding process ( means bonding of dissimilar metal) during the rolling operation & then hammering to get No.4 sheet forms.

20. F. Carbonized or corrugated foil • Gold foil is carbonised by heating in an air –tight Co2 containing chamber • Shrivelled or corrugated foil is formed • Dentist can prepare the ropes or cylinders from this

21. II . Electrolytic precipitate • Another from of DFG is Microcrystalline gold powder formed by electrolytic precipitation

22. 1 . Sub types A. Mat gold B. Mat foil (mat gold plus gold foil) C. Electralloy {Gold – calcium alloy}

23. A. MAT GOLD (SPONGY ,CRYSTALLINE) • Is obtained from electrolytic precipitation on the cathode gold plate surface • Produced Powder consist of Dendritic crystal (0.1mm in length), is then heated (sintering ) to a temperature below the M.P (1063*c) of gold, Sintering makes the crystal to coalesce & grow together. • Powder is then formed into strips of 3-6 mm width & 15 mm long • Mat gold is sometimes called spongy crystalline gold .

24. B. Mat – foil gold • Electrolytic precipitate gold powder is sandwiched, between sheets of No.3 gold foil, sintered & cut into pieces • More preferred for building up the internal bulk of the restoration ( because compaction can be done more easily in a shorter time) • But after condensation more voids remains between the particles.

25. C.Electralloy {Gold – calcium alloy} • Mat gold is alloyed with 0.1% calcium. • Calcium alloy electrolytic precipitate powder is obtained . • This is sandwiched between gold foil & sintered, formed into thin strips • Calcium increases the strength. • This Electralloy has higher hardness

26. III Granular (powdered gold ) • 1st used in early 1960’s • Gold powder is in agglomerated form , prepared by chemical precipitation or atomization from the molten gold • EZ gold • Stop foil gold

27. A. EZ gold • Chemically precipitated & atomized gold powder are first mixed with a soft wax to form pellets or cylinders of 1-2 mm size & are wrapped with no.3 gold foil • Before insertion into the cavity wax is burnt away & removed

28. B. Stop foil gold • Prepared by keeping chemically precipitated gold powder, in between gold foil & then sintering, then cut into strips & pieces for use

29. Desorption heat treatments of DFG

30. Removal of Surface Impurities(desorption) • Prior to the insertion of DFG, dentist heats the material to remove protective coating (ammonia gas) or wax introduced by the manufacturer or contaminants on the surface (moisture or gases -O2,N2,H2) acquired during storage & packing • Process of removing gases (or other), impurities from the surface of gold is called - Annealing, heat treatment, degassing or desorption

31. Objectives of desorption heat treatment • Improves the hardness and strength of compacted gold • Also helps for better welding • Drives away impurities from the surface, thus making the surface ready for cohesive • To keep this surface devoid of any other impurities, until complete cohesion occurs during buildingup of the restoration

32. Heating time vary depending on the types & size of DFG • For Powdered gold – 15-20 sec • For Gold foil pellets & electrolytic gold pellet - 1-2 sec • Chamois finger tips should be worn by the dentist to protect the gold from contamination. • Temperature- 600-13000F • Under heating should be avoided because it does not adequately remove the impurities • Overheating should be avoided because excessive sintering causes the material to become more stiffer, less ductile and difficult to condense

33. Methods of desorption Gold can be heated in two ways • Flame annealing /Alcohol flame method - heating piece by piece • Hot plate annealing -heating bulk in a tray • For gold foil & mat gold – either method is acceptable • But for powdered gold – flame annealing is acceptable

34. 1.Flame Heating ( Heating piece by piece)

35. 1.Flame Heating ( heating piece by piece) • For flame annealing, handle the pieces with stainless steel wire point (because of less contamination). • In this individual pellets are held over an alcohol flame (ethanol or methanol) and heating is done piece by piece • Pellet catches fire and burns until volatile substance is eliminated and exhibits a dull red glow , and then it is removed and carried to the cavity for condensation • Insufficient heating of the pellet causes it to be “powdery”

36. Advantages of flame desorption • Ability to select a piece of appropriate size. • Desorption of only those pieces used • Less exposure to contamination. • Less danger of over sintering • Control of time and temperature

37. 2.Hot plate Annealing – heating bulk in a tray

38. In this method, numerous Pellets are being heated simultaneously on a mica tray over a gas flame or electric hot furnaces for 10 min at 454*c . • Hot plate annealing needs more pre-heating and also utilizes lower temp than flame annealing . • Over-heating – causes brittleness and stiffness • Under- heating – causes gold pellet noncohesive and does not stick

39. Electric Annealer

40. DISADVANTAGES • Use of excessive amounts of pellets should be avoided, because it requires prolong heating • Pellets may stick together, if the tray is moved. • Air currents may affect the uniformity of heating • Difficulty of selection of particular type • Over sintering • Greater exposure to contamination. • Less control over the time and temp • Slightly delayed compacted, results in adsorption of gases

41. Precautions • Temp – 350-700*c , DFG should become just red hot • Source – Pure alcohol, reduced zone (pale blue region) of the flame used • Time – of heating should be properly controlled (15-60 sec ) • Only required amount should be taken in the tray ,

42. COMPACTION OF DFG • Condensation is the procedure used to condense and fill the harden gold inside the prepared cavity by cold welding method • Totally dry cavity is mandatory through out the compaction process to ensure complete cohesion • Incremental technique can be maintained for compaction • Cavity first designed with required undercuts and retention points ( as DFG cannot chemically bond) • In case of deep cavity, pulp protecting insulating base should be used

43. COMPACTION OF DFG • 2 main process • Cold - Welding • Wedging

44. Cold - Welding: • Process of joining metals by metallic bonding by applying pressure between the two parts to be joined • Here metal –joining process does not occurs by heating or fusing

45. Wedging • Wedging refers to the pressurized adaptation of the gold form within the space between the tooth structure walls or corners that have been slightly deformed elastically.

46. Instrument used • Hand condenser & mallet. • Pneumatic vibratory condensers. • Electrically driven condensers.

47. Hand condenser

48. Hand mallet & condenser

49. Pneumatic condenser

50. Condenser • Condenser can be straight, curved, angled, round, square, or rectangular • Surface of the tip is smooth or serrated • Tip can be flat or convex faced • Size of the tip is about 1-3 mm • Too thin tip may pierce and damage the restoration • Too larger tip cannot be effective in producing sufficient pressure