precious metal alloys, gold alloys, dental materials, dental alloys

1. Vinay Pavankumar .K
1ST Year P.G
Department of Prosthodontics
AECS Maaruti Dental College

2. Precious
metal alloys
Classification
Composition
Properties
History
Alloy
Treatment of
noble and high
noble alloys

3. Alloy
A mixture of two or more metals or metalloids that
are mutually soluble in the molten state;
distinguished as binary, ternary, quaternary, etc.,
depending on the number of metals within the
mixture.
Two or more metals that are mutually soluble in
each other in the molten state.

4. Noble metal
 Those metal elements that resist oxidation,
tarnish, and corrosion during heating, casting, or
soldering and when used intraorally; examples
include gold and platinum.
Good metallic surface that retain their surface in
dry air.
Eight noble metals
Metallurgists consider silver a noble metal, but it
is not considered a noble metal in dentistry

5. Precious metal alloy
Precious metal: a metal containing primarily elements of
the platinum group, gold, and silver.
Precious metal alloy: an alloy predominantly composed of
elements considered precious, i.e., gold, the six metals of
the platinum group (platinum, osmium, iridium, palladium,
ruthenium, and rhodium), and silver
Term precious stems from the trading of these metals on
the commodities market

7. HISTORICAL PERSPECTIVE ON PRECIOUS
METAL & ALLOYS IN DENTISTRY
C. Spence Bate at the 1883,annual meeting of the British
Dental Association, in Plymouth, entitled `A Review of the
Scientific Progress of Dental Surgery from 1771 to 1883,
contains the passage:
“We must congratulate ourselves on the great improvement
that has taken place in the power of retaining diseased
teeth and restoring to usefulness such as would, a few
years ago, have been considered hopelessly
irrecoverable. The extent of this process of repair can
best be understood by saying that, independent of
amalgam and cement stoppings, 20 000 ounces [620 kg]
of fine gold is annually used in filling teeth ...”

8. As early as the seventh centry B.C Etruscan dental
prostheses made by passing thin strips of gold round
teeth on each side of a space from which a tooth or
teeth had been lost and rivetting the strip so as to
hold the substitute teeth in place.

9.  The discoveries were dated back to 550 B.C . A canine
tooth like object made of two piece of calcite having
hardness similar to natural teeth showing wear on the
chewing surface & secured with gold wires wrapped around
the neck of adjacent teeth

10.  The first printed book on dentistry, entitled
'ArtzneyBuchlein' ('The Little Pharmacopaeia'), was
published by Michael Blum in Leipzig in 1530. Under
this title or as 'Zene Artznei' ('Dental Medicine')
“Scrape and clean the hole and the area of decay with a
fine small chisel or a little knife or a file, or with
another suitable instrument, and then to preserve the
other part of the tooth, fill the cavity with gold leaves.”

11.  Maggilio in 1809 , a dentist at the university of Nancy ,
France, author of the book called “THE ART OF THE
DENTIST”. The first reference to modern style implants.
He has described the implant & placement.
He made the tooth root shaped implant with 18 carat
gold with three prongs at the end to hold it in place in the
bone . The implant was placed in the freshly extracted
socket site retained with the prongs. After the tissues
healed the crown was attached with the help of post
placed into the hole of root section of the implant. He
placed the single stage gold implant.

12. In 1886 Harris treated a Chinese patient in Grass valley ,
California . He placed the tooth root shaped platinum post with
lead coating, lasted for 27 yrs Reported in Dental Comos.
In 1888, Charles Henry Land who fused porcelain on thin
platinum caps for use as crowns. This technique is still used in
making jacket crowns.
 In 1890, a Massachusetts minister had his lower jaw
resected & was restored with an extensive system of gold
crowns soldered & joined to hinged device attached to the
remaining dentition

13.  Bonwill in 1895 reported on the implantation of one
or two tubes of gold or Iridium as a support for
individual teeth or crown.
 In 1898 R. E Payne at the National Dental
Association meeting gave the first clinical
demonstration by placing the silver capsule in the
extracted tooth socket.
 In 1896 B. F.Philbrook, attempted to make soft,
fusible metal inlays by a lost wax process, he fitted
several white metal inlays and one gold inlay.

14. In 1897 George B. Martin demonstrated gold dummy
or artificial teeth, called `pontics', for use on fixed
bridges; these were soldered to gold crowns on the
abutment teeth.
In 1900, J. G.Schottler used a method to restore the
biting edges of front teeth by placing a platinum wire
in the root canal, building the required shape on the
tooth with wax. Invested and casted it in gold.
In 1906 John A. Lenz obtained a patent for devising
a method for lost wax casting a gold chewing surface
onto a gold band made to fit around a tooth.

15. At a meeting of the New York Odontological Society
on January 15, 1907, William H.Taggart of Chicago
read a lecture entitled `A New and Accurate Method of
Casting Gold Inlays' in which he described a lost wax
technique which can truly be said to have
revolutionized restorative and prosthetic dentistry

16.  In 1907, a Dr. Solbrig, in Paris. introduced his
casting pliers which achieved enormous popularity
for the rapid production of small inlays.
 In 1913 Dr. Edward J. Greenfield, fabricated the
hollow cylindrical basket root of 20 gauge
iridioplatinum soldered with 24 carat gold.
 The recent development of gold abutment
retainaing screws and cylinder.

17. Gold
Soft, rich yellow color and a strong metallic luster
Most malleable and ductile
0.2% lead – brittle
Soluble in aqua regia
Alloyed with copper, silver, platinum – increases hardness ,
durability and elasticity

18. Platinum
 Bluish white metal
 Hardness similar to copper
 Higher melting point ( 1772°C) than porcelain
 Coefficient of thermal expansion close to porcelain
 Lighten the color of yellow gold based alloys
 Common constituent in precision prosthetic attachments

19. Silver (Ag)
Malleable, ductile; white metal.
Stronger and harder than gold, softer than copper.
Absorbs oxygen in molten state-difficult to cast
Forms series of solid solutions with palladium and
gold .
 Neutralizes reddish color of alloys containing
copper

20. Palladium (Pd)
 White metal darker than platinum
 Density little more than half that of Pt and Au
 Absorbs hydrogen gas when heated
 Not used in pure state in dentistry
 Whitens yellow gold based alloys.

21. Iridium(Ir ) Ruthenium(Ru ), Rhodium(Rh) &
Osmium(Os)
Grain refiners
Improves mechanical properties and uniformity of
properties within alloy
Extremely high melting point of Ir - 2410°C and Ru -
2310°C – serve as nucleating centers
Osmium(Os) has a very high melting point, and is very
expensive, hence not used in dentistry.

22. Physical properties of noble and precious
metals

23. Mechanical properties of noble and precious
metals

24. History of Dental casting alloy
 1907 : Lost wax process technique -W H Taggart.
 1932 : Classification of gold based casting alloys.
 1933 : Introduction of Co-Cr and Ni-Cr alloys.
 1959 : Porcelain-fused to metal prothesis.
 1971 : End of Bretton Woods system.
 1976 : The medical and dental devices act.
 1996 : European medical devices directive.
 1998 : The clean air act.

25. Classification of dental casting alloys:
According to their use:
All metal inlays
Crowns and bridges
Metal ceramic prothesis
Post and cores
Removable partial dentures.
Implants
According to major elements :
•Gold based
•Palladium based
•Silver based
•Nickel based
•Cobalt based
•Titanium based
According Dominant Phase system:
• Single
• Eutectic
• Peritectic
• Intermetallic

26. Alloy Classification by Noble Metal Content
Alloy type Total noble metal content
High noble (HN) Contain ≥40 wt% Au and ≥60 wt% of noble
metal elements (Au, Pt, Pd, Rh , Ru, Ir, Os)
Noble (N) Contain ≥25 wt% of noble metal elements
Predominantly
Base metal (PB)
Contain <25wt% of noble metal elements

27. In 2003, the Council for Scientific Affairs revised the classification
to include titanium in a separate category because of its
extensive usage and similar properties with noble metals
class Required
noble
content (%)
Required
gold
content (%)
Required
titanium content
(%)
High noble
alloys
≥60 ≥40
Titanium and
titanium alloys
≥85
Noble alloys ≥25
Predominantly
base metals
≥25
Givan A A, Precious Metals in Dentistry, Dent Clin N Am vol 51 2007;591-601

28. Classification of Mettallic Materials for Dental
Application ISO 22674 (2006)
Type Yield Strength
(Mpa)
Elongation
(%)
Examples of Application
0 -- -- Single fixed tooth fixed restorations
1 80 18 Single fixed tooth fixed restorations
veneered or non veneered
2 180 10 For Single fixed tooth fixed restorations
3 270 5 For multiple unit fixed restorations
4 360 2 For appliances with this cross sections
that are subject to very high forces
5 500 2 For thin removable partial dentures,
parts with thin cross sections

29. According to yield strength and percentage elongation
(proposed in ISO draft international standard 1562 for casting
gold alloys 2002)
Alloy type Hardness Yield
strength
(MPa)
Percent
elongation
%
Type 1: Low strength Soft 80 18
Type 2:Medium
strength
Medium 180 10
Type 3: high strength Hard 270 5
Type 4: Extra-high
strength
Extra
hard
360 3

30. Classification of casting metals for full metal, Metal
Ceramic and Partial Dentures
Metal
type
All metal Metal Ceramic Partial Denture
High
noble
Au-Ag-Pd
Au-Pd-Cu-Ag
Au-Pt-Pd
Au-Pd-Ag (5-12 wt% Ag)
Au-Pd-Ag (>12 wt% Ag)
Au-Pd
Au-Ag-Cu-Pd
Noble Ag-Pd-Au-Cu
Ag-Pd
Pd-Au
Pd-Au-Ag
Pd-Ag
Pd-Cu-Ga
Pd-Ga-Ag

31. Desirable properties of casting alloys
Biocompatibility
Tarnish and Corrosion resistance
Compatible thermal properties
Castability
Aesthetics
Economical

32. Functional Mechanical Properties of Casting alloys
 Elastic modulus
Yield strength
Ductility
Hardness
Fatigue Resistance

33. Selected properties of major types of high-noble alloys
Alloy
type
Solidus-
liquidus
(C)
Color Phase
structure
Elastic
modulus
(staticGPa)
Vicker’s
hardness
(kg/mm2)
Yield
strength
(tension,
0.2%, Mpa)
Au-Pt (Zn) 1060–
1140
Yellow Multiple 65–96 165–210 360–580
Au-Pd
(Ag)
1160–
1260
White Single 105 280 385
Au-Cu-Ag 905–960 White Single 100 210 450

34. Mechanical properties of noble and precious metal
casting alloys

35.  Treatment of noble and high noble alloys
 Type lll and type lV gold alloys can be hardened and
softened.
 Softening heat treatment/homogenizing-Solution heat
treatment.
 Hardening heat treatment-Age hardening.

36. Softening Heat Treatment
 Increases ductility
 reduces tensile strength ,proportional limit and hardness
Method:
 Casting placed in electric furnace
 10 minutes,700°Cquenched in water resulting disordered
solid solution
 Indicated-alloys that are to be ground, shaped or otherwise
cold worked either in or out of mouth.

37. Hardening of Noble metals
Increases strength, proportional limit, and hardness, but
decreases ductility
If positioning of two elements become ordered-ordered
solution
Copper present in gold alloy helps in this process.
Method:
Soaking/ageing casting-15 to 30 minutes before water
quenching 200°C to 450°C
Ideally, before age hardening it should first be subjected
to softening heat treatment

38. Alloys for metal ceramic prosthesis
Classification of Noble PFM alloys
Au Based Pd Based
Au-Pt-Pd (21 K) Pd-Ag
Au- Pd (13 K) Pd-Cu
Au-Pd-Ag (13 K) Pd-Co

39. Noble alloys
 Gold-copper-silver-
palladium
 Palladium-copper-gallium
 Palladium-silver and silver-
palladium
High noble alloys
 Gold-Platinum alloy
 Gold-Palladium alloy
 Gold-copper-silver-palladium
alloys

40. Physical and Chemical properties
1. Noble metal content
2. Hardness
3. Yield strength
4. Elongation
5. Fusion temperature
6. Porcelain-Metal Compatibility
7. Color stability
8. Biocompatibility

41. Typical properties of alloys for PFM restorations

42. High noble alloys
 Minimum of 60% noble metals (any combination of
gold, palladium and silver) with a minimum of 40% by
weight of gold.
 Tin, indium and/or iron oxide layer formation
chemical bond for the porcelain.

43. Gold-platinum alloy
Developed alternative to palladium alloys
For full cast as well as metal-ceramic restorations.
 More prone to sagging, they should be limited to
short span bridges.
 A typical composition is Gold 85%;
 Platinum12%;
 Zinc 1%;
 Silver (in few brands)

44. Gold-palladium alloy
Used for full cast /metal-ceramic restorations.
Palladium - high melting temperature
- impart a white or gray color
- improves sag resistance
 These alloys usually contain indium, tin or gallium to
promote an oxide layer.
A typical composition
 Gold 52%;
 Palladium 38%;
 Indium 8.5%;
 Silver (in some brands).

45. Gold-copper-silver-palladium alloy
 Have low melting temperature
 Not used for metal-ceramic applications.
 Greening of porcelain – due to silver
 Copper tends to cause sagging during porcelain
processing.
A typical composition is
 Gold 72%,
 Copper 10%;
 Silver 14%;
 Palladium 3%.

46. Noble alloys
 Contain at least 25% by weight of noble metal (gold,
palladium or silver)
 Have relatively high-strength, durability, hardness, ductility.
 They may be yellow or white in color.

47. Gold–copper-silver-palladium alloy
 More copper and silver
 Have a fairly low melting temperature
 More prone to sagging during application of porcelain.
 Used mostly for full cast restorations rather than PFM
applications.
 A typical formula is: gold 45%
 Copper 15%
 Silver 25%
 Palladium 5%

48. Palladium-copper-gallium alloys
 Introduced in 1983
 Very rigid excellent full cast or PFM restorations.
 Contain copper  prone to sagging during porcelain firing.
 Gallium  reduces the melting temperature
A typical composition is
 Palladium 79%
 Copper 7%;
 Gallium 6%
 Hardness is comparable to base metal alloy but are not
burnishable

49. Palladium-silver and silver-palladium alloys
 Higher palladium alloys - PFM frameworks.
 Higher silver alloys - susceptible to corrosion
- greening of porcelain
 High resistance to sagging
 very rigid - good for long spans

50.  More castable (more fluid in the molten state)
 Easier to solder and easier to work with than the base
metal alloys.
 Typical composition for Palladium- silver alloy:
 Palladium 61%; silver 24%; Tin (in some)
Silver-palladium alloy:
 Silver 66%; Palladium 23%; gold (in some
formulation)

51. Greening
 Discoloration of porcelain
 Due to silver ions
 Mechanism not clear
 Cervical region
 Metal - ceramic interface
 Prevented -silver free alloys
 metal coating agents

52. Precious metals & dental implants
GOLD UCLA-TYPE ABUTMENTS
• 64% gold, 22% palladium
• Melting range 2400˚F-2500˚F (1320˚C-1370˚C)
• Gold alloy abutment screw retention increases the preloading
force there by assuring precision fit to implant
Ceraone & Mirus cone abutments
• SEMI-BURNOUT CYLINDER
Non-oxidizing, high precious gold platinum alloy with a plastic
wax-up sleeve Cylinder base
Alloy Melting range Coefficient of thermal
linear expansion
Plastic sleeve
Burnout
temperature
Au 60%, Pt 24%,
Pd 15%, Ir 1%
1400–1460°C/
2552-2660°F
25–500°C 12.3 (10–6K-1)
25–600°C 12.7 (10–6K-1
700°C/1292°F

53. Review of literature
 The study evaluated the cervical and internal fit of complete
metal crowns that were cast and recast using palladium-silver
alloy and 3 different marginal configurations used were
straight shoulder, 20-degree bevel shoulder, and 45-degree
chamfer.
 Results showed - The new alloy provided significantly better
adaptation than the recast alloy for both marginal and internal
discrepancy measurements. Marginal designs did not shown
any statistical differences when the new metal was used
Lopes,S.Consani et al ,Influence of recasting palladium-silver alloy on the fit
of crowns with different marginal configurations
J Prosthet dent,2005;94,5:430-434

54. • This study evaluated the influence of a composite
interlayer (at the metal–ceramic interface) on the shear
bond strength of a metal–ceramic composite when
compared with a conventional porcelain fused to metal
(PFM).
The shear bond strength results for all composites
bonded to metal and to ceramic substrates were
significantly higher (>150 MPa) than those registered in
the upper range of conventional porcelain fused to
metal (PFM) techniques (∼80 MPa). The use of a
composite interlayer proved to enhance metal/ceramic
adhesion in 160%.
B. Henriques et al. Optimization of bond strength between gold alloy and porcelain
through a composite interlayer obtained by powder metallurgy .Materials Science and
Engineering A 528 (2011) 1415–1420

55. The aim of this study were to investigate the fatigue limits of two Pd–
Ag alloys (Ivoclar Vivadent) with differing mechanical properties and
varying proportions of secondary alloying elements, examine the
effect of casting porosity on fatigue behavior,and determine the effect
of casting size on microstructures and Vickers hardness
Tension test bars, heat-treated to simulate dental porcelain
application, were subjected to cyclic loading at 10 Hz, with R-ratio of
−1 for amplitudes of compressive and tensile stress. Two replicate
specimens were tested at each stress amplitude. Fracture surfaces
were examined with a scanning electron microscope (SEM).
Sectioned fatigue specimens and additional cast specimens
simulating copings for a maxillary central incisor restoration were
also examined with the SEM, and Vickers hardness was measured
using 1 kg load. Casting porosity was evaluated in sectioned fatigue
fracture specimens, using an image analysis program.
•Baba.D.Li.N etal, Study of Pd–Ag dental alloys: examination of effect of casting porosity on
fatigue behavior and microstructural analysis Journal of Materials Science: Materials in
Medicine October 2010, Volume 21, Issue 10, pp 2723-2731

56. relatively low ratios of fatigue limit to 0.2% yield strength are similar to those
found previously for high-palladium dental alloys, and are attributed
to their complex microstructures and casting porosity.
Complex fatigue fracture surfaces with striations were observed forboth
alloys. Substantial further decrease in the number of cycles for fatigue failure
only occurred when the pore size and volume percentage became
excessive.
While the heat-treated alloys had equiaxed grains with precipitates, the
microstructural homogenization resulting from simulated porcelain firing
differed considerably for the coping and fatigue test specimens; the latter
specimens had significantly higher values of Vickers hardness.
•Baba.D.Li.N etal, Study of Pd–Ag dental alloys: examination of effect of casting
porosity on fatigue behavior and microstructural analysis Journal of Materials
Science: Materials in Medicine October 2010, Volume 21, Issue 10, pp 2723-2731

57. CONCLUSION

58. References
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60.  Lopes,Consani S et al, Influence of recasting palladium-silver alloy
on the fit of crowns with different marginal configurations, J Prosthet
dent;94,5:430-434
 B. Henriques et al. Optimization of bond strength between gold alloy
and porcelain through a composite interlayer obtained by powder
metallurgy .Materials Science and Engineering A 528 (2011) 1415–
1420
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