gold

2. INTRODUCTION

3.  Since antiquity, pure gold has been a
metal of special intrinsic and practical
value. From the dawn of civilization until
the present time, man has utilized gold in
some form or other in the practice of
dentistry.

4. In its pure form, gold has the unusual
ability to cohere to it self at room
temperature. Gold is quite soft, and in a
compressible form, increments can be
welded by pressure into a solid metal
mass.

5. Another unique feature about gold is it
inertness. Under most conditions it does
not tarnish, corrode or stain.

6.  Its chief disadvantages are its color, high
thermal conductivity(53.20), and technical
difficulties in forming a dense restoration.
It has one of the highest densities of all
elements (19.3 g/cm3)

7. Indications;
 Incipient carious lesions
Class I and pits
Class V
Class III
 Erosions
 Repair of defective cast margins

8. Advantages: 
 No tarnish and corrosion
 Insoluble in oral cavity
 Good adaptation to cavity walls
 High wear resistance

9. Disadvantages
Colour
Manipulation
Thermal conductivity

11. They are Classified into three categories:
II. Foil
A. Sheet
1. Cohesive
2. Noncohesive
B. Ropes
C. Cylinders
D. Laminated foil
E. Platinized foil

12. I. Electrolytic precipitate
A. Mat gold
B. Mat foil (mat gold plus gold foil)
C. Gold – calcium alloy

13. III Powdered gold (encapsulated gold
powder)

14. Gold Foil ( Robert
Woffendale 1795)
Oldest of all products standard No. 4 Gold foil
4 x 4 inch sheets weight 4 grains (0.259g) and
0.51µm thick
No. 3 weight 3 grains – 3 µm thick.

15. Cohesive - Noncohesive
Gold:
Gold attracts gases and any adsorbed gas
film prevents intimate atomic contact
required for cold welding
- Manufactures supply free of surface

16. NON COHESIVE FOIL:
Majority are provided with an adsorbed
protective gas film like ammonia
-
Prevents premature cohesion of sheets
that may come into contact. Volatile film
is removed by heating to restore the
cohesive character of the foil.

17. Gold Foil Cylinders:
Formed by rolling cut segments of
No. 4 foils into a desired width
- 3.2mm, 4.8mm, 6.4mm using modified
No.22 tapestry needle.

18. Preformed Gold Foils:
 Cylinders and ropes are now
available in preformed shapes made
from No.4 foil which has been
‘carbonised’ or corrugated
• Historical interest Great Chicago fire of
1871

19. Platinised Gold Foil:
 It is a laminated structure can be
produced in
one of the 2 ways.
4. 2 sheets of No.4 pure gold foil and a
layer of pure platinum foil sandwiched
between there can be hammered until
the thickness of No.4 sheet is obtained.

20. 2. Layers of platinum and gold can
be bonded together by cladding
process during the rolling
operation.
Objective of adding platinum:
Increases hardness and wear
resistance

21. Electrolytic Precipitate:
 Crystalline gold powder formed by
electrolytic precipitation.
 Powder is formed by sintering at an
elevated temp. well below the melting point of
gold, it causes self diffusion between
particles where they are in contact.

22. Mat Gold ( Rule 1937)
Is a crystalline, electrolytically
precipitated gold form that is formed
into strips .Preferred ease in building
up the internal bulk, more easily
compacted within and adapted to the
retentive portion of the prepared
cavity.

23. Disadvantages:
 Because it is loosely packed it is
friable and contain numerous void
spaces.
 2- material technique mat is
covered with a veneer of foil.

24. Mat foil
Sandwich of electrolytic precipitated
gold powder between sheets of No.3
gold foil
Purpose – Try to eliminate the need
to veneer the restoration with a layer of
foil
No longer Marketed

25. Alloyed electrolytic
precipitate
The newest forms of electrolytic
precipitate electro alloy RV is alloyed
with calcium. Calcium content of the
finished product is about 1%
Purpose is to produce stronger
restoration by dispersion strengthening

26. Powdered Gold:
1st used in early 1960’s
Gold powder was enclosed in No. 3
gold foil .maximum particle size is 74
µm Avg 15 µm

27. The atomized and chemically
precipitated powders are
1st mixed with a soft wax to form pellets
These wax – gold pellets wrapped with
foil

28. Removal of Surface
Impurities:
With the exception of non cohesive
gold the DFGs are received by the
dentist in a cohesive condition.
During storage and packaging they are
exposed to the atmosphere

29. It is necessary to heat the foil or pellet
before it is carried into the prepared
cavity. It is called
Annealing, heat treatment, degassing a
more appropriate term is desorption. It
is essential to achieve a cohesive mass.

30. Chamois finger tips should be worn by the
dentist to protect the gold from
contamination.

31. Proper desorption is a matter of heating
long enough at a temperature that removes
gases and in case of powdered gold burns
away the wax.
Temperatures in the range of 600-13000F
must be produced
Under heating should be avoided because it
does not adequately remove the impurities

32. Overheating should be avoided because
excessive sintering causes the material to
become more stiffer less ductile and
difficult to condense.
- Too Long time
- Too high temperature
Temperatures below 3150C are inadequate

33. The Gold can be heated in
two ways
1.Flame Heating
Flame annealing, held The alcohol flame
near the top of the is transparent; the
flame, flame from the
pellets is visible

34. 2.Electric Annealing
Pellets are being heated on
a tray

35. When heating in bulk on a tray, excessive
amounts should be avoided, since the
difficulties arising from prolonged
heating can arise, from repeated heating
as well.

36. Handle the pieces with stain less steel wire
points that will not contaminate the gold.
Flame desorption occurs when the gold
segment has exhibited a dull red glow.

37. The fuel may be alcohol or gas but
alcohol is preferred because there is less
danger of contamination.
Alcohol must be pure methanol or
ethanol without colorants or additives.

38. Advantages of flame desorption
3. Ability to select a piece of
appropriate size.
4. Desorption of only these pieces used.
5. Less exposure to contamination.
6. Less danger of over sintering

39. DISADVANTAGES OF ELECTRIC ANNEALING
- Pellets may stick together, if the tray is
moved.
- Air currents may effect the uniformity of
heating
- Difficult to anneal appropriate amounts of
gold.

40. - Oversintering.
- Greater exposure to contamination.
- Size selection among the pieces of
desorbed gold is limited.

41. COMPACTION OF DIRECT FILLING
GOLD
Condensation is the procedure used to
condense and harden gold inside the cavity
preparation
2 main process
6. Welding
7. Wedging

42. Welding:
Forming atomic bonds between pellets or
layer as result of condensation.

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

44. Straight points are cut in the prepared
cavity and the 1st pieces of foil are
wedged into these areas

45. COMPACTION:
Can be done by:
3. Hand mallet.
4. Pneumatic vibratory condensers.
5. Electrically driven condensers.

46. a. Nichrome wire used for carrying gold;
b. Pneumatic condenser
c. Detachable condensing tins

47. PHYSICAL PROPERTIES OF COMPACTED GOLD
1. Strength and Hardness:
BHN of pure gold is 25. During
condensation its hardness rises to 75.
Tensile strength rises from 19000 psi to
32000 psi.
Yield strength rises from 0 to 30,000 psi

48. 3) Density:
Density of pure gold is 19.3. Density of
well compacted direct gold is 16.5 cm3
The difference is due to the presence of
porosity and voids
4. Melting point of Gold-1063O C

49. 5.Tarnish and Corrosion Resistance:
Is good, there is very little marginal
leakage between the filling and cavity
walls, if the compaction is good.
6. It dissolves in aqua regia
7. high thermal conductivity (.710cal /sec

50. 6 Biocompatibility:
It is biocompatible. Produces
only a minimal pulpal response, if
compacted properly. The technique,
however, does involve a certain amount of
trauma to the tooth and its supporting
tissues.