Dental Amalgam Overview and History

Amalgam Overview

• Amalgam is an alloy of mercury with one or more other metals
• Dental amalgam alloy contains silver, tin, copper, and sometimes zinc
• Dental Amalgam is formed when mercury combines with the previously mentioned alloys, forming a plastic mass
• Amalgamation or trituration is the process of mixing the alloy with liquid mercury
• Amalgamators or triturators are mechanical devices used for this process

History of Amalgam

• 1819: English chemist Bell invented mercury-based dental amalgam fillings
• 1826: Dental amalgam fillings used in England and France
• 1830: Crawcour brothers introduced amalgam to the US
• 1840: The first amalgam war occurred, The American Society of Dental Surgeons denounced the use of amalgam
• 1859: Pro-mercury amalgam factions in America (ADA) ended the first amalgam war
• 1895: G.V. Black formulated the formula for modern amalgam alloy (67% silver, 27% tin, 5% copper, 1% zinc)

Amalgam Composition and Properties

• Silver (Ag): Increases strength, increases expansion.
• Tin (Sn): Decreases expansion, decreases strength, increases setting time.
• Copper (Cu): Ties up tin, reducing gamma-2 formation, increases strength, reduces marginal corrosion
• Mercury (Hg): Activates reaction, the only pure metal liquid at room temperature.
• Zinc (Zn): Decreases oxidation, sacrificial anode, better clinical performance, less marginal breakdown.
• Indium (In): Decreases surface tension, reduces the amount of necessary mercury, reduces emitted mercury vapor, reduces marginal breakdown, increases strength, must be used in admixed alloys
• Palladium (Pd): Reduced corrosion, greater luster. Example: Valiant PhD (Ivoclar Vivadent), commonly 0.5% palladium

Amalgam Setting and Reactions

• The setting reaction starts with trituration, progressing with condensation and carving
• Working time of amalgam is not directly controlled by the dentist (unlike light-activated composites)
• Amalgam is a direct restorative material held in place by mechanical retention (undercuts and grooves).
• A silver-mercury matrix holds filler particles of silver-tin (Ag3Sn - called gamma)
• Gamma can have different shapes (irregular, spherical, a combination)
• Matrix includes Ag2Hg3 (called gamma 1, cement), and Sn8Hg (called gamma 2, voids).
• Types of Amalgam Alloy Setting Reactions: Conventional low-copper, Admixed high-copper
• In conventional low-copper alloys, Hg dissolves Ag and Sn from the alloy, forming intermetallic compounds.
• In high-copper alloys, Ag enters the Hg from Ag-Cu spherical particles, and Ag & Sn enter the Hg from Ag3Sn particles. Sn diffuses to Ag-Cu particles forming Cu6Sn5 around unconsumed Ag-Cu particles.

Amalgam Handling and Properties

• Spherical advantages: easier condensation, faster hardening, smoother polish
• Spherical disadvantages: difficulty achieving tight contacts, higher tendency for overhangs
• Admixed advantages: easier to achieve tight contacts, good polish
• Admixed disadvantages: hardens slowly, lower early strength
• Amalgam Properties: Dimensional change happens during the amalgamation reaction; expansion and contraction occur simultaneously. Overall dimensional change is the sum of these two processes and is affected by factors such as moisture contamination, particle size and shape, type of the alloy and manipulation during the processes.

Amalgam Classifications

• Based on copper content (Low-copper, High-copper)
• Based on particle shape (Lathe-cut, Spherical, Admixed)

Amalagam Manufacturing Process

• Lathe-cut: Ag & Sn melted together, cooled, heat treated (400°C for 8 hours), ground to 25-50 microns, then heat treated to relieve stresses
• Spherical: Melt alloy, atomize, and spheres form as particles cool ranging from 5-40 microns in size

Amalgam Properties and Considerations

• Strength: High compressive strength but low tensile and shear strength. Requires sufficient bulk(1.5-mm or more thickness) and support to withstand occlusal forces; it should last approximately 10-20 years.
• Creep: Slow shape change due to compression. Used to be a good indicator of clinical performance, but the clinical performance no longer correlates with creep when high copper amalgams are developed compared to those with lower copper.
• Tarnish: Oxidation, dark dull appearance; not destructive
• Corrosion: Galvanic corrosion occurs with dissimilar metals in a wet environment (like the mouth). Surface corrosion discolors and can pit; it also fills the tooth/amalgam interface with corrosion products reducing microleakage
• Clinical Aspects (patient behavior): Acidic environment, poor oral hygiene, and cariogenic diets promotes galvanic corrosion. These promote caries leading to accelerated corrosion, therefore impacting amalgam durability/longevity.
• Mercury Safety: Should be considered (operator, patient, environment). Hg enters the body via skin contact, vapor inhalation, and ingestion. To protect patient, use high volume suction and rubber dam isolation.

Working and Setting Times

• Fast-set and slow-set versions of amalgam are sold
• Fast-set versions set faster than regular-set versions, usually, but not always.

This quiz covers the essential aspects of dental amalgam, including its composition, historical development, and the processes involved in its creation. Test your knowledge on the key events and figures that contributed to the evolution of dental amalgam since its invention in the early 19th century.