precious metal alloys in dentistry
DESCRIPTION
precious metal alloys, gold alloys, dental materials, dental alloysTRANSCRIPT
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Precious metal alloys
Vinay Pavankumar .K
1ST Year P.G
Department of Prosthodontics
AECS Maaruti Dental College
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Precious metal alloys
Classification
Composition
Properties
History
Alloy
Treatment of noble and high
noble alloys
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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.
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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
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Precious metal alloyPrecious 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
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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 ...”
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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.
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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
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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.”
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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.
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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
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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.
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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.
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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
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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.
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Gold
Soft, rich yellow color and a strong metallic lusterMost malleable and ductile0.2% lead – brittleSoluble in aqua regiaAlloyed with copper, silver, platinum – increases hardness ,
durability and elasticity
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Platinum
Bluish white metalHardness similar to copperHigher melting point ( 1772°C) than porcelainCoefficient of thermal expansion close to porcelainLighten the color of yellow gold based alloysCommon constituent in precision prosthetic attachments
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Silver (Ag)
Malleable, ductile; white metal.Stronger and harder than gold, softer than copper. Absorbs oxygen in molten state-difficult to castForms series of solid solutions with palladium and
gold . Neutralizes reddish color of alloys containing
copper
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Palladium (Pd)
White metal darker than platinumDensity little more than half that of Pt and AuAbsorbs hydrogen gas when heatedNot used in pure state in dentistry Whitens yellow gold based alloys.
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Iridium(Ir ) Ruthenium(Ru ), Rhodium(Rh) & Osmium(Os)
Grain refinersImproves mechanical properties and uniformity of
properties within alloy Extremely high melting point of Ir - 2410°C and Ru -
2310°C – serve as nucleating centersOsmium(Os) has a very high melting point, and is very
expensive, hence not used in dentistry.
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Physical properties of noble and precious metals
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Mechanical properties of noble and precious metals
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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.
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Classification of dental casting alloys:
According to their use: All metal inlaysCrowns and bridgesMetal ceramic prothesisPost and coresRemovable 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
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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
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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
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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
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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
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Classification of casting metals for full metal, Metal Ceramic and Partial Dentures
Metal type
All metal Metal Ceramic Partial Denture
High noble
Au-Ag-PdAu-Pd-Cu-Ag
Au-Pt-PdAu-Pd-Ag (5-12 wt% Ag)Au-Pd-Ag (>12 wt% Ag)
Au-Pd
Au-Ag-Cu-Pd
Noble Ag-Pd-Au-CuAg-Pd
Pd-AuPd-Au-Ag
Pd-AgPd-Cu-GaPd-Ga-Ag
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Desirable properties of casting alloys
BiocompatibilityTarnish and Corrosion resistance Compatible thermal propertiesCastabilityAesthetics Economical
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Functional Mechanical Properties of Casting alloys
Elastic modulus
Yield strength
Ductility
Hardness
Fatigue Resistance
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Selected properties of major types of high-noble alloys
Alloy type
Solidus-liquidus(C)
Color Phasestructure
Elasticmodulus(staticGPa)
Vicker’shardness(kg/mm2)
Yieldstrength(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
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Mechanical properties of noble and precious metal casting alloys
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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.
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Softening Heat Treatment Increases ductility reduces tensile strength ,proportional limit and hardness
Method:Casting placed in electric furnace10 minutes,700°Cquenched in water resulting disordered
solid solution Indicated-alloys that are to be ground, shaped or otherwise
cold worked either in or out of mouth.
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Hardening of Noble metals Increases strength, proportional limit, and hardness, but
decreases ductilityIf positioning of two elements become ordered-ordered
solutionCopper present in gold alloy helps in this process.
Method:Soaking/ageing casting-15 to 30 minutes before water
quenching 200°C to 450°CIdeally, before age hardening it should first be subjected
to softening heat treatment
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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
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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
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Physical and Chemical properties1. Noble metal content2. Hardness3. Yield strength4. Elongation5. Fusion temperature6. Porcelain-Metal Compatibility7. Color stability8. Biocompatibility
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Typical properties of alloys for PFM restorations
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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.
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Gold-platinum alloyDeveloped 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)
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Gold-palladium alloyUsed 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).
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Gold-copper-silver-palladium alloyHave 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%.
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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.
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Gold–copper-silver-palladium alloyMore 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%
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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
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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
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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)
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Greening Discoloration of porcelainDue to silver ionsMechanism not clear
Cervical regionMetal - ceramic interface
Prevented -silver free alloys metal coating agents
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Precious metals & dental implantsGOLD 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 sleeveBurnout
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
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Review of literatureThe 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
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• 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
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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
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relatively low ratios of fatigue limit to 0.2% yield strength are similar to those found previously for high-palladium dental alloys, and are attributedto 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
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CONCLUSION
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