Dental Amalgam Flashcards by Aivee Privado

An alloy, one of the constituents of which is mercury

Silver Paste

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An alloy made by mixing Hg with Ag-Sn dental amalgam alloy

Silver Paste

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Increases expansion
Retards setting time
Enhances strength
Decrease flow
Resist tarnish/corrosion

Silver

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Unites with Hg with difficulty
Reduces setting time
Increases expansion
Increases strength and hardness
Reduces flow

Copper

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Combines readily with Hg
Retards setting time
Improves platsicity
Reduces expansion
Increases flow

Tin

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Combines readily with Hg
Causes expansion increases setting time
Increases flow
Inhibits oxidation 
Decreases porosity
Provides better clinical performance

Zinc

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Other Constituents of Dental Amalgam

Indium (In)
Palladium (Pd)
Mercury (Hg)

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Decreases surface tension
Reduces amount of mercury necessary
Reduces emitted mercury vapor
Reduces creep and marginal breadown
Increases strength
Must be used in admixed alloys
5%

Indium (In)

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Reduces corrosion
Greater luster
e.g. Vallant PhD (Ivoclar Vivadent)
0.5%

Palladium (Pd)

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Activates reaction

Only pure metal that is liquid at room temperature

Mercury (Hg)

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Classification of Amalgam

Amalgam alloy particle geometry and size
Copper content
Zinc content

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Irregular particle pack poorly and require a large amount of Hg (50-60%)
Precapsulated amalgam (spherical) has 42-45% Hg

Alloy-Mercury ratio

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Require less Hg
Smaller surface area, easier to wet
40 to 45%

Spherical Alloys

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Reaction of Amalgam

Mercury + Silver-Tin -> Silver-Tin phase + Silver-Mercury phase + Tin-Mercury Phase

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Called the gamma phase

Composed of unreacted alloy particle

Silver-Tin Phase

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Ag3Sn
Unreacted alloy
Strongest phase and corroded the least
Forms 30% of volume set amalgam

Gamma

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The amount of mercury needed to wet all particles and occupy the space between the particles range from ____________ mercury by weight

40-60%

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Called the gamma one

Silver-Mercury Phase

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Ag2Hg3
Matrix for unreacted alloy
Second strongest phase
10 micron grains binding gamma
60% of volume

Gamma 1

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Called the gamma two

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Tin-Mercury Phase

Sn8Hg
Weakest and softest phase
Corrodes fast,
Voids from corrosion yeilds Hg which reacts with more gamma
10% of volume
Volume decreases with time due to corrosion

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Gamma 2

2 phenomenon during hardening of amalgam

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Solution

Crystallization

When Hg comes in contact with amalgam alloy, the particles are wt by mercury and begins to absorb it
The solution of mercury into silver-tin particles leads to the formation of the surface of Ag-Hg and Sn-Hg phases
The crystallisation of the gamma1 and 2 phases and their subsequent growth leads to hardening of amalgam

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Crystallisation

Factors affecting Setting Time (4)

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Effect of alloy/mercury ratio
Condensation pressure
Particle size
Particle shape

More mercury increases expansion - as well as setting time

Effect of alloy/mercury ratio

As the condensation pressure increases, the tendency for shrinkage increases. Increased condensation pressure results in removal of more excess mercury and a faster setting reaction

Condensation Pressure

As the particle size decreases, the total particle surface area increases. This results in a faster setting reaction, as long as no additional mercury is added. Amalgams made from smaller dental amalgam alloy particles shrink more as long as the mercury ratio is not high

Particle size

Spherical particles need less mercury because of the smaller total surface area. Thus, spherical amalgams often set faster than lathe-cut amalgams. Because of the lower mercury ratio, spherical amalgams often shrink more than lathe-cut alloys

Particle Shape

Properties of amalgam

Dimensional change | Strength

Causes amalgam to expand and contract Diffusion of mercury into alloy particles causes an expansion Spherical alloys have more contraction (less Hg) Greater condensation = higher contraction

Dimensional Change

Amalgam does not develop sufficient strength to resist the forces pf mastication Tensile strength - 7100 psi Compressive strength - 45,500 psi Develops slowly

Strength

Dentist Controlled Variable

Manipulation

4 properties under manipulation

Trituration Condensation Burnishing Polishing

Process of manual mixing of alloy with Hg Done by proportioning Hg and alloy into a mortar grinding the mixture with a pestle Mixing time refer to manufacturers recommendation

Trituration

Sticks to capsule Decrease working and setting time Causes higher contraction

Overtrituration

Grainy, crumbly material

Undertrituration

Types of trituration

Hand | Mechanical

Done by proportioning Hg and alloy into a mortar and grinding the mixture with a pestle

Hand trituration

Use of amalgamator

Mechanical trituration

A hallow tube with rounded ends constructed as two pieces that could friction fit or screwed together

Reusable capsule

Pre-proportioned

Precapsulated

Phases of Burnishing

Pre-carve Post-carve Combined

Removes excess mercury | Improves margin adaptation

Pre-carve

Improves smoothness

Post-carve

Less leakage

Combined

Increased smoothness Decreased plaque retention Decreased corrosion Clinically effectivev

Polishing

Uses squeeze cloth to remove excess mercury

Mercury rich mixtures

Illness associated with mercury

Allergies, chronic fatigue, depression, GI disorders, immune system suppression, endocrine disorders, periodontal disease, neurological problems, reproductive disorders, birth defects, kidney disease, heart problems, hypertension, repiratory disorder, cancer, and skin disease

Sources of mercury

Mercury vapours released from stored materials Amalgamator aerosols Spillage during restoration procedure Amalgam and mercury in plumbing and sewer system Amalgam scrap container

Dental Amalgam Flashcards

(49 cards)