Dental Amalgam:Dental Amalgam:Material Properties and itsMaterial Properties and itsUse in Clinical DentistryUse in Clinical Dentistry

Prepared by:Prepared by:

Zirgham HafeezZirgham Hafeez

Group #611Group #611

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

• The silver-gold binary system is an example The silver-gold binary system is an example of a continuous solid solution. Silver and of a continuous solid solution. Silver and gold are completely miscible in each other gold are completely miscible in each other in the solid state. Nearly all pairs of metals in the solid state. Nearly all pairs of metals are miscible in the solid state, but only a are miscible in the solid state, but only a few are continuously miscible across the few are continuously miscible across the entire range of composition in the solid entire range of composition in the solid state.state.

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

W eight 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

• The silver-tin binary system contains an area of The silver-tin binary system contains an area of solid solution in which tin is soluble in silver up to solid solution in which tin is soluble in silver up to around 9 atomic percent tin. Above that level of around 9 atomic percent tin. Above that level of tin, additional phases precipitate out as tin, additional phases precipitate out as intermetallic compounds. Of particular dental intermetallic compounds. Of particular dental interest in this diagram is the composition of 25 interest in this diagram is the composition of 25 atomic percent tin, 75 atomic percent silver, which atomic percent tin, 75 atomic percent silver, which is the gamma phase, Agis the gamma phase, Ag33Sn. This phase Sn. This phase constitutes the main phase in the unreacted constitutes the main phase in the unreacted amalgam particles.amalgam particles.

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

• The silver-mercury system also exhibits a The silver-mercury system also exhibits a solid solubility region, in which mercury solid solubility region, in which mercury forms a solid solution with silver up to forms a solid solution with silver up to about 35 atomic percent mercury. Above about 35 atomic percent mercury. Above that composition, various intermetallic that composition, various intermetallic compounds form. The principal phase that compounds form. The principal phase that is of interest in dentistry is the gamma is of interest in dentistry is the gamma phase, Agphase, Ag22HgHg33, which is usually referred to , which is usually referred to as “gamma-1” to distinguish it from the as “gamma-1” to distinguish it from the gamma phase in the silver-tin system.gamma phase in the silver-tin system.

Reaction: Low-Copper AlloysReaction: Low-Copper Alloys

Ag3Sn() + Hg Ag2Hg3(1) + Sn7-8Hg(2) + Ag3Sn()

Low-copper alloys were used from the late 1800’s till the 1970’s, but are rarely used today. The reaction of low-copper alloys with mercury produces a corrosion-prone phase, Sn7-8Hg, which is the gamma phase of the mercury-tin system. To distinguish it from the gamma phases of the silver-tin and silver-mercury systems, the Sn7-8Hg gamma phase is usually referred to as the gamma-2 phase.

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