Dental Amalgam Overview and History

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Questions and Answers

What is the minimum thickness of dental amalgam required to withstand occlusal forces effectively?

2.5 mm

1.5 mm (correct)

1.0 mm

2.0 mm

Which factor is NOT a cause of tarnish on dental amalgam?

Excessive heat during mixing (correct)

Sulfide interaction

Oxygen exposure

Chloride contact

Which type of corrosion affects dental amalgam due to the presence of dissimilar metals in a wet environment?

Oxidative corrosion

Galvanic corrosion (correct)

Chemical corrosion

Cavitation corrosion

What can reduce microleakage at the tooth/amalgam interface?

Surface corrosion products Signup and view all the answers

What common misconception about creep in dental amalgam does recent evidence indicate?

Creep provides an accurate measure of clinical performance. Signup and view all the answers

Which of the following is NOT a safety consideration regarding mercury in dental procedures?

Post-procedure patient diet Signup and view all the answers

What primarily influences the longevity of dental amalgam restorations?

Patient behavior and oral hygiene Signup and view all the answers

What is the effect of using high-volume suction during dental procedures that involve amalgam?

Reduces mercury exposure Signup and view all the answers

What is the primary method used to produce lathe-cut dental amalgam particles?

Grinding an ingot of metal to produce filings Signup and view all the answers

Which of the following characters can be attributed to spherical dental amalgam alloys?

Easier to condense around pins Signup and view all the answers

What is a significant disadvantage of using spherical dental amalgam alloys?

Difficult to achieve tight contacts Signup and view all the answers

What are admixed or blended alloys a combination of?

Spherical and lathe-cut particles Signup and view all the answers

What is the primary function of indium in dental amalgam?

Decreases surface tension Signup and view all the answers

Which phase of dental amalgam has the highest strength and the lowest corrosion rate?

Gamma (Ag3Sn) Signup and view all the answers

Which factor does NOT affect dimensional change during the amalgamation reaction?

Ambient temperature Signup and view all the answers

What is the primary advantage of using high-copper alloys in dental amalgam?

Reduced expansion and corrosion Signup and view all the answers

What is a potential outcome of overtrituration of dental amalgam?

Decreased setting time Signup and view all the answers

How does the shape of particles in an amalgam affect the material properties?

Admixed shapes optimize both mechanical properties and handling Signup and view all the answers

During which process can excessive expansion occur in dental amalgam?

When moisture contaminates zinc-containing alloys Signup and view all the answers

What effect does corrosion in the gamma 2 phase have on dental amalgam?

Can potentially release mercury vapor Signup and view all the answers

What is the recommended heating condition for lathe-cut alloys to release stresses from grinding?

400 ºC for 8 hours Signup and view all the answers

What is the typical copper content in low-copper dental alloys?

4 to 6% Signup and view all the answers

During the setting reaction of amalgam, what occurs during trituration?

Alloy components dissolve in mercury Signup and view all the answers

What are the three classifications of dental amalgam based on its particle shape?

Lathe-cut, spherical, admixed Signup and view all the answers

Study Notes

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.

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Description

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.