Dental Amalgam Material Properties and its Use in

Dental Amalgam: Material Properties and its Use in Clinical Dentistry J. Rodway Mackert, Jr. , DMD, Ph. D Medical College of Georgia Augusta, Georgia

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

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

Alloy Powder Composition Type Ag Low copper Sn Cu Zn Other 2 -7 0 -2 — 40 -70 26 -30 12 -30 0 -2 — 63 -72 26 -28 High-Cu admixed lathe-cut High-Cu admixed spherical High-Cu unicomp- ositional spherical 40 -65 0 -30 20 -40 0 0 -1 Pd 40 -60 22 -30 13 -30 0 -5 In, 0 0 -1 Pd compositions in weight percent

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

® Alloy Powder: Tytin Mixing proportions: 57. 5% alloy, 42. 5% mercury

Amalgam Capsules • Contain (in separate compartments): – powdered amalgam alloy – liquid mercury • Some are manually activated, others selfactivated • Pestle usually included

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

Silver-Gold Phase Diagram

Silver-Tin Phase Diagram

Silver-Mercury Phase Diagram

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

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)

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 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. )

Properties of Mercury • Only liquid metal at room temperature • Evaporation 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

Université Laval 3. 7 -m LMT

Courtesy of E. F. Borra, Université Laval

Hg Evaporation from Amalgam • Baseline Hg vaporization rate (unstimulated) from amalgam in humans is 0. 027 ng·cm 2·s– 1 • Average vaporization rate (over 24 -h period) in humans is 0. 048 ng·cm 2·s– 1 • The evaporation rate of Hg from amalgam is 800– 1500 times lower than from oxidized mercury

Mercury Dose from Amalgam • Person 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/day • According to EPA, absorbed dose of mercury from food, water, and air is 5. 7 µg/day

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