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Dental Amalgam: Material Properties and its Use in Clinical Dentistry.

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Presentation on theme: "Dental Amalgam: Material Properties and its Use in Clinical Dentistry."— Presentation transcript:

1 Dental Amalgam: Material Properties and its Use in Clinical Dentistry

2 What is Amalgam? a·mal·gam: any alloy of mercury with another metal or other metals [silver amalgam is used as a dental filling] a·mal·gam: any alloy of mercury with another metal or other metals [silver amalgam is used as a dental filling] Source: Websters New World Dictionary of the American Language, Guralnik DB, Ed., New York: World Publishing Co., Source: Websters New World Dictionary of the American Language, Guralnik DB, Ed., New York: World Publishing Co., 1972.

3 Types of Dental Amalgam Copper amalgam (no longer used)Copper amalgam (no longer used) Conventional (low-copper) amalgam: formulation standardized in 1890sConventional (low-copper) amalgam: formulation standardized in 1890s High copper amalgam: first developed in the 1960sHigh copper amalgam: first developed in the 1960s

4 Alloy Powder Composition TypeAgSnCuZnOther Low copper High-Cu admixed lathe-cut High-Cu admixed spherical Pd High-Cu unicomp- ositional spherical In, 0-1 Pd compositions in weight percent

5 Alloy Powder: Dispersalloy ® Mixing proportions: 50% alloy, 50% mercury

6 Alloy Powder: Tytin ® Mixing proportions: 57.5% alloy, 42.5% mercury

7 Amalgam Capsules Contain (in separate compartments):Contain (in separate compartments): –powdered amalgam alloy –liquid mercury Some are manually activated, others self- activatedSome are manually activated, others self- activated Pestle usually includedPestle usually included

8 Amalgamator (Triturator) Speeds vary upward from 3000 rpmSpeeds vary upward from 3000 rpm Times vary from 5–20 secondsTimes vary from 5–20 seconds Mix powder and liquid components to achieve a pliable massMix powder and liquid components to achieve a pliable mass Reaction begins after components are mixedReaction begins after components are mixed

9 Silver-Gold Phase Diagram

10 Silver-Tin Phase Diagram

11 Silver-Mercury Phase Diagram

12 Reaction: Low-Copper Alloys Ag 3 Sn( ) + Hg Ag 2 Hg 3 ( 1 ) + Sn 7-8 Hg( 2 ) + Ag 3 Sn( )

13 Reaction: High-Copper Alloys Ag 3 Sn( ) + Ag-Cu + Hg Ag 2 Hg 3 ( 1 ) + Sn 7-8 Hg( 2 ) + Ag 3 Sn( ) + Ag-Cu and Sn 7-8 Hg( 2 ) + Ag-Cu Cu 6 Sn 5 ( ) + Ag 2 Hg 3 ( 1 )

14 Composition of Set Amalgam Matrix of 1 (Ag 2 Hg 3 ) and (Cu 6 Sn 5 ) phases, with embedded particles of unreacted (Ag 3 Sn) and Ag-Cu phasesMatrix of 1 (Ag 2 Hg 3 ) and (Cu 6 Sn 5 ) phases, with embedded particles of unreacted (Ag 3 Sn) and Ag-Cu phases Not a solid emulsion (...it is not correct to refer to an aggregate of intermetallic compounds, all of which are solid at room temperature, as a solid emulsion. Laurier Schramm, author of Dictionary of Colloid and Interface Science.)Not a solid emulsion (...it is not correct to refer to an aggregate of intermetallic compounds, all of which are solid at room temperature, as a solid emulsion. Laurier Schramm, author of Dictionary of Colloid and Interface Science.)

15 Properties of Mercury Only liquid metal at room temperatureOnly liquid metal at room temperature Evaporation rateEvaporation rate –Theoretical maximum is 57.9 µg·cm 2 ·s –1 from pristine, oxide-free surface into a vacuum (= 57,900 ng·cm 2 ·s –1 ) –Measured rate in vacuum is ~40 µg·cm 2 ·s –1 (= ~40,000 ng·cm 2 ·s –1 ) –Oxidation of Hg lowers rate by factor of 1000

16 Université Laval 3.7-m LMT

17 Courtesy of E.F. Borra, Université Laval

18 Hg Evaporation from Amalgam Baseline Hg vaporization rate (unstimulated) from amalgam in humans is ng·cm 2 ·s –1Baseline Hg vaporization rate (unstimulated) from amalgam in humans is ng·cm 2 ·s –1 Average vaporization rate (over 24-h period) in humans is ng·cm 2 ·s –1Average vaporization rate (over 24-h period) in humans is ng·cm 2 ·s –1 The evaporation rate of Hg from amalgam is 800–1500 times lower than from oxidized mercuryThe evaporation rate of Hg from amalgam is 800–1500 times lower than from oxidized mercury

19 Mercury Dose from Amalgam Person with average number of fillings (7) would absorb ~1.6 µg/dayPerson with average number of fillings (7) would absorb ~1.6 µg/day Person with a moderately high number of fillings (13) would absorb ~3 µg/dayPerson with a moderately high number of fillings (13) would absorb ~3 µg/day According to EPA, absorbed dose of mercury from food, water, and air is 5.7 µg/dayAccording to EPA, absorbed dose of mercury from food, water, and air is 5.7 µg/day

20 Jerome Mercury Vapor Analyzer Used by many anti- amalgam dentists to measure intra-oral mercury vaporUsed by many anti- amalgam dentists to measure intra-oral mercury vapor Differences in sampling volumes and flow rates must be taken into account, or gross errors will resultDifferences in sampling volumes and flow rates must be taken into account, or gross errors will result

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