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Dental Amalgam:Dental Amalgam:Material Properties and itsMaterial Properties and itsUse in Clinical DentistryUse in Clinical Dentistry
What is Amalgam?What is Amalgam?
a·mal·gama·mal·gam: any alloy of mercury with another : any alloy of mercury with another metal or other metals [silver metal or other metals [silver amalgamamalgam is used is used as a dental filling]as a dental filling]††
††Source: Source: Webster’s New World Dictionary of the American Webster’s New World Dictionary of the American LanguageLanguage, Guralnik DB, Ed., New York: World Publishing , Guralnik DB, Ed., New York: World Publishing Co., 1972.Co., 1972.
Types of Dental AmalgamTypes of Dental Amalgam
• Copper amalgam (no longer used)Copper amalgam (no longer used)
• Conventional (low-copper) amalgam: Conventional (low-copper) amalgam: formulation standardized in 1890’sformulation standardized in 1890’s
• High copper amalgam: first developed in High copper amalgam: first developed in the 1960’sthe 1960’s
Alloy Powder CompositionAlloy Powder Composition
TypeType AgAg SnSn CuCu ZnZn OtherOther
Low copperLow copper 63-7263-72 26-2826-28 2-72-7 0-20-2 ——
High-Cu admixed High-Cu admixed lathe-cutlathe-cut
40-7040-70 26-3026-30 12-3012-30 0-20-2 ——
High-Cu admixed High-Cu admixed sphericalspherical
40-6540-65 0-300-30 20-4020-40 00 0-1 Pd0-1 Pd
High-Cu unicomp- High-Cu unicomp- ositional sphericalositional spherical
40-6040-60 22-3022-30 13-3013-30 000-5 In, 0-5 In, 0-1 Pd0-1 Pd
compositions in weight percentcompositions in weight percent
Alloy Powder: DispersalloyAlloy Powder: Dispersalloy®®
Silver69%
Tin18%
Copper12%
Zinc1%
Mixing proportions: 50% alloy, 50% mercury
Alloy Powder: TytinAlloy Powder: Tytin®®
Mixing proportions: 57.5% alloy, 42.5% mercury
Silver59%
Tin13%
Copper28%
Zinc0%
Amalgam CapsulesAmalgam Capsules
• Contain (in separate Contain (in separate compartments):compartments):– powdered amalgam powdered amalgam
alloyalloy
– liquid mercuryliquid mercury
• Some are manually Some are manually activated, others self-activated, others self-activatedactivated
• Pestle usually includedPestle usually included
Amalgamator (Triturator)Amalgamator (Triturator)
• Speeds vary upward Speeds vary upward from 3000 rpmfrom 3000 rpm
• Times vary from 5–20 Times vary from 5–20 secondsseconds
• Mix powder and liquid Mix powder and liquid components to achieve components to achieve a pliable massa pliable mass
• Reaction begins after Reaction begins after components are mixedcomponents are mixed
Sil
ver-
Gol
d P
hase
Dia
gram
Sil
ver-
Gol
d P
hase
Dia
gram
0 10 20 30 40 50 60 70 80 90
961.93°
100
1064.4°
Atomic Percent Ag
L
Au
0 10 20 30 40 50 60 70 80 90 100
950
960
970
980
990
1000
1010
1020
1030
1040
1050
1060
1070Te
mpe
ratu
re (
°C)
W eight Percent
Sil
ver-
Tin
Pha
se D
iagr
amS
ilve
r-T
in P
hase
Dia
gram
0 10
13°
20
221°
30 40
480°
50 60 70
724°
80 90
-Sn
-Sn
96.2
231.968°
100
Atomic Percent
Weight Percent
Ag
(Ag)
Sn
0 10 20 30 40 50 60 70 80 90 100
0
100
200
300
400
500
600
700
800
900
1000
Tem
pera
ture
(°C
)
961.93°
L
Sil
ver-
Mer
cury
Pha
se D
iagr
amS
ilve
r-M
ercu
ry P
hase
Dia
gram
0 10 20
276°
127°
30
40
44.837.3
56.8
50 60 70 80 90
99.7
99.3
96
100
Atomic Percent
W eight Percent
Ag
(Ag)
L
Hg
0 10
961.93°
20 30 40 50 60 70 80 90 100
-100
0
100
200
300
400
500
600
700
800
900
1000
Tem
pera
ture
(°C
)
-Hg
Reaction: Low-Copper AlloysReaction: Low-Copper Alloys
Ag3Sn() + Hg Ag2Hg3(1) + Sn7-8Hg(2) + Ag3Sn()
Reaction: High-Copper AlloysReaction: High-Copper Alloys
Ag3Sn() + Ag-Cu + Hg Ag2Hg3(1) + Sn7-8Hg(2) + Ag3Sn() + Ag-Cu
and
Sn7-8Hg(2) + Ag-Cu Cu6Sn5() + Ag2Hg3(1)
Composition of Set AmalgamComposition of Set Amalgam
• Matrix of Matrix of 11 (Ag (Ag22HgHg33) and ) and (Cu (Cu66SnSn55) )
phases, with embedded particles of phases, with embedded particles of unreacted unreacted (Ag(Ag33SnSn) and Ag-Cu phases) and Ag-Cu phases
• Not a “solid emulsion” (“...it is not correct Not a “solid emulsion” (“...it is not correct to refer to an aggregate of intermetallic to refer to an aggregate of intermetallic compounds, all of which are solid at room compounds, all of which are solid at room temperature, as a solid emulsion.” —temperature, as a solid emulsion.” —Laurier Schramm, author of Laurier Schramm, author of Dictionary of Dictionary of Colloid and Interface ScienceColloid and Interface Science.).)
Properties of MercuryProperties of Mercury
• Only liquid metal at room temperatureOnly liquid metal at room temperature
• Evaporation rateEvaporation rate– Theoretical maximum is 57.9 µg·cmTheoretical maximum is 57.9 µg·cm22·s·s–1–1 from from
pristine, oxide-free surface into a vacuum (= pristine, oxide-free surface into a vacuum (= 57,900 ng·cm57,900 ng·cm22·s·s–1–1))
– Measured rate in vacuum is ~40 µg·cmMeasured rate in vacuum is ~40 µg·cm22·s·s–1–1 (= (= ~40,000 ng·cm~40,000 ng·cm22·s·s–1–1))
– Oxidation of Hg lowers rate by factor of 1000Oxidation of Hg lowers rate by factor of 1000
Université Laval 3.7-m LMTUniversité Laval 3.7-m LMT
M ercu ry va p o r con cen tratio n a s fu n ctio n o f tim e
0
0.04
0.08
0.12
0.16
0.20
0 5 10 15 20
Tim e (hours)
Hg
vap
or c
once
ntr
atio
n (m
g/m
³)
25
0.9 mm2 mm4 mm
M ercu ry va p o r con cen tratio n a s fu n ctio n o f tim e
0
0.04
0.08
0.12
0.16
0.20
0 5 10 15 20
Tim e (hours)
Hg
vap
or c
once
ntr
atio
n (m
g/m
³)
25
0.9 mm2 mm4 mm
Courtesy of E.F. Borra, Université Laval
Hg Evaporation from AmalgamHg Evaporation from Amalgam
• Baseline Hg vaporization rate Baseline Hg vaporization rate (unstimulated) from amalgam in humans is (unstimulated) from amalgam in humans is 0.027 ng·cm0.027 ng·cm22·s·s–1–1
• Average vaporization rate (over 24-h Average vaporization rate (over 24-h period) in humans is 0.048 ng·cmperiod) in humans is 0.048 ng·cm22·s·s–1–1
• The evaporation rate of Hg from amalgam The evaporation rate of Hg from amalgam is 800–1500 times lower than from is 800–1500 times lower than from oxidizedoxidized mercurymercury
Mercury Dose from AmalgamMercury Dose from Amalgam
• Person with average number of fillings (7) Person with average number of fillings (7) would absorb ~1.6 µg/daywould absorb ~1.6 µg/day
• Person with a moderately high number of Person with a moderately high number of fillings (13) would absorb ~3 µg/dayfillings (13) would absorb ~3 µg/day
• According to EPA, absorbed dose of According to EPA, absorbed dose of mercury from food, water, and air is mercury from food, water, and air is 5.7 µg/day5.7 µg/day
Jerome Mercury Vapor AnalyzerJerome Mercury Vapor Analyzer
• Used by many anti-Used by many anti-amalgam dentists to amalgam dentists to measure intra-oral measure intra-oral mercury vapormercury vapor
• Differences in Differences in sampling volumes and sampling volumes and flow rates must be flow rates must be taken into account, or taken into account, or gross errors will result gross errors will result
0 µg/m ³
0 sec
250 m L32 µg/m ³
Room Air: Jerome Instrument
Room Air: Jerome Instrument
20 sec
32 µg/m ³
250 m L32 µg/m ³
Room Air: Human Respiration
0 µg/m ³
0 sec 32 µg/m ³
500 m L
Room Air: Human Respiration
32 µg/m ³
500 m L
32 µg/m ³2½ sec
JeromeInstrum ent
(20 sec)
Hum anRespiration(2½ sec)
0 sec
250 mL
1 ng Hg
500 mL
5 sec 10 sec 20 sec15 sec2½ sec 7½ sec 12½ sec 17½ sec
In tra-O ral A irJerom e Instrum ent vs. H um an R esp ira tion
In tra-O ral A irJerom e Instrum ent vs. H um an R espira tion
Jerom eInstrum ent
(20 sec)
250 mL
Hum anRespiration
(2½ sec)
1 ng Hg
500 mL
250 mL
8 ng= 32 µg/m ³
500 mL
1 ng= 2 µg/m ³