Dental Amalgam Manufacturing Process

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Questions and Answers

What is the primary function of zinc in dental amalgam?

To act as a deoxidizer (correct)

To enhance aesthetic qualities

To increase mechanical strength

To reduce setting time

What type of dental amalgam consists of spherical and irregular silver alloy particles?

Admixed amalgam (correct)

Copper-rich amalgam

Spheroidal amalgam

Lathe-cut amalgam

What is the purpose of homogenization heat treatment in the manufacturing of dental amalgam?

To form an intermetallic compound

To reduce the size of the particles

To eliminate excess mercury

To improve mechanical properties and corrosion resistance (correct)

Which process involves melting and atomizing constituent elements into water to create powder?

Spheroidal powder production Signup and view all the answers

What is a consequence of aging or annealing heat treatment on dental amalgam powder?

It eliminates internal stresses Signup and view all the answers

What is the first step in the manufacturing process of dental amalgam?

Ingot production Signup and view all the answers

At what temperature is the homogeneous heat treatment of the cored ingot conducted?

400 °C Signup and view all the answers

What is formed when dental amalgam alloy is mixed with mercury?

A plastic mix that is placed into the prepared cavity Signup and view all the answers

What is the primary advantage of spherical particles in dental amalgam over lath cut particles?

They produce amalgam with superior mechanical properties. Signup and view all the answers

During the amalgamation reaction, which phase results from the surface reaction between mercury, silver, and tin?

Ag2Hg3 phase Signup and view all the answers

What happens to the amalgam properties when excess mercury is present?

Strength decreases and corrosion resistance decreases. Signup and view all the answers

What is one of the main objectives of condensation in dental amalgam manipulation?

Decrease the mercury content by expressing excess mercury to the surface Signup and view all the answers

Which phase in the microstructure of dental amalgam is the strongest and most resistant to corrosion?

Ag3Sn (ɤ) Signup and view all the answers

What is the recommended time frame for performing condensation after trituration?

Within 3 minutes Signup and view all the answers

What is the first stage of the amalgamation reaction when mixing mercury with alloy powder?

Wetting Signup and view all the answers

What can result from delayed condensation beyond 3 minutes from trituration?

Decreased strength due to breaking up of partially formed matrix Signup and view all the answers

What effect does the elimination of the Sn8Hg (ɤ2) phase have on dental amalgam properties?

Improves dental amalgam properties. Signup and view all the answers

What is the consequence of fewer voids in the microstructure of dental amalgam?

Increased resistance to corrosion. Signup and view all the answers

Why is the cavity overfilled prior to carving in dental amalgam manipulation?

To remove the top mercury-rich layer effectively Signup and view all the answers

Which process directly follows the wetting stage in the amalgamation reaction?

Diffusion Signup and view all the answers

When should finishing and polishing be performed for high copper amalgam?

Shortly after insertion Signup and view all the answers

What is one of the primary objectives of finishing and polishing dental amalgam?

Increase corrosion resistance by obtaining a smooth surface Signup and view all the answers

What can lead to leakage at the tooth-restoration interface?

Contraction of the restoration Signup and view all the answers

What is a potential consequence of expansion of a restoration?

Tooth fracture or protrusion from the cavity Signup and view all the answers

What is the primary benefit of increasing the copper content in high copper amalgam?

Elimination of Sn8Hg (ɤ2) phase Signup and view all the answers

What are the two main types of particles used in admixed high copper amalgam?

Silver-copper eutectic and silver-tin alloy Signup and view all the answers

During the solid-state reaction in high copper amalgam, which phase is slowly eliminated?

Sn8Hg (ɤ2) phase Signup and view all the answers

Which characteristic is typical of the microstructure of unicompositional high copper amalgam?

Ag2Hg3 (ɤ1) matrix surrounding unreacted particles Signup and view all the answers

What is one drawback of admixed high copper amalgam?

Surface oxidation of the silver-copper eutectic alloy Signup and view all the answers

What does the setting reaction for high copper amalgam involve?

Two distinct reactions: amalgamation and solid-state Signup and view all the answers

What role does the Ag-Cu eutectic play in the amalgamation reaction?

It remains unreacted Signup and view all the answers

How is the unicompositional high copper amalgam characterized in terms of particle composition?

Contains only Ag3Sn and Cu3Sn phases Signup and view all the answers

What is the maximum dimensional change allowed by ADA specifications for dental amalgam?

20 mm/cm Signup and view all the answers

What causes the initial contraction of dental amalgam within the first 30 minutes of setting?

Solubility of amalgam powder by mercury Signup and view all the answers

Delayed expansion in zinc-containing amalgam can occur when exposed to which condition?

Moisture during trituration or condensation Signup and view all the answers

What is the primary reason for recommending zinc-free amalgam in specific patient populations?

Difficulty achieving isolation Signup and view all the answers

Which factor contributes to net contraction in modern dental amalgam?

Mechanical amalgamators with low Hg/powder ratio Signup and view all the answers

What effect does the evolution of hydrogen gas from zinc reaction with water have during delayed expansion?

Leads to post-operative sensitivity and blistering Signup and view all the answers

Which of the following statements about creep in dental amalgam is correct?

It occurs after the complete setting of amalgam restoration. Signup and view all the answers

What leads to the marginal adaptation of dental amalgam restorations?

Good condensation and the self-seal property of dental amalgam Signup and view all the answers

What is one of the primary clinical significances of creep in dental amalgam?

Marginal breakdown (ditching) Signup and view all the answers

Which factor does NOT contribute to the creep of dental amalgam?

High compressive stress Signup and view all the answers

What is the primary method to decrease creep in dental amalgam?

Using high copper alloy Signup and view all the answers

How long does dental amalgam take to reach 80% of its final strength?

1 hour Signup and view all the answers

What cavity preparation technique maximizes the strength of a dental amalgam restoration?

Maintaining a 90-degree cavo-surface angle Signup and view all the answers

What is the effect of corrosion on dental amalgam?

Decreases strength and releases metals Signup and view all the answers

What is the primary bonding mechanism between dental amalgam and tooth structure?

Macro-mechanical retention Signup and view all the answers

Which factor is LEAST associated with improving the properties of dental amalgam?

Using a lower copper content Signup and view all the answers

Study Notes

Amalgam

Amalgam is any alloy containing mercury.
Dental amalgam alloy is an alloy made from silver, tin, and copper. Zinc is sometimes added.
Dental amalgam is produced by mixing dental amalgam alloy with mercury at room temperature. This gives a plastic mix that's placed into a cavity.

Composition of dental amalgam alloy

Dental amalgam alloy's composition includes silver, tin, copper, and sometimes zinc.
Silver constitutes 69% of the alloy.
Tin makes up 18% of the alloy.
Copper comprises 12% of the alloy.
Zinc accounts for 1% of the alloy.

Composition of dental amalgam

The main role of silver is to control the reaction between silver and mercury.
Tin controls the reaction between silver and mercury.
Copper plays a role in the mix of the restoration.
Mercury is the liquid that makes up the plastic mix of the restoration.

Role of zinc

Zinc acts as a scavenger (deoxidizer).
Zinc improves plasticity during condensation.

Classification of dental amalgam

Classification is based on particle shape.
- Lathe cut (irregular)
- Spherical
- Spheroidal
Classification is based on copper content.
- Low copper
- High copper
- Admixed
- Unicompositional
Classification is based on zinc content.
- Zinc containing
- Zinc free

Percentage composition of dental amalgam alloy

The percentage composition of silver, tin, copper, and zinc in low copper and high copper amalgam is presented.

Manufacturing of dental amalgam

Ingot production: The constituent elements are melted and cast into a cylindrical ingot (3.8 x 25 cm). Then it is slowly cooled under 480°C.
- An intermetallic compound Ag3Sn(γ phase) is produced.
Homogenous heat treatment: The cored ingot is subjected to homogenization heat treatment to improve mechanical properties and corrosion resistance. This is done by heating to 400°C for 24 hours.
Powder production:
- Lathe cut: The ingot is cut or milled into irregular particles.
- Spherical: The constituent elements are melted and atomized (sprayed) into inert gas.
- Spheroidal: The constituent elements are melted and atomized (sprayed) into water.
Aging or annealing heat treatment:
- Aging: Store the powder at room temperature for several months.
- Annealing: Heat the powder at 100°C for 1-6 hours.
- Spherical & spheroidal require homogenization heat treatment only; they don't need aging/annealing.

Advantages of spherical particles over lathe cut

Lower surface area, requiring less mercury to obtain a homogenous mix.
Produces amalgam with superior properties and increases corrosion resistance.
Produces a smooth surface during carving and finishing.
Requires less condensation pressure.

Amalgamation reaction

Amalgamation reaction involves a series of phases (γ, γ1, γ2, η, ε) with their compositions.
Low copper amalgam: The powder is mainly Ag3Sn (γ Phase).
- Wetting: liquid mercury is added and triturated.
- Diffusion: mercury diffuses into silver and tin.
- Surface reaction: mercury reacts with silver and tin leading to new phases.
The new phases increase over time, hardening the mix.
The new phases surround the unreacted parts of the mix.

Setting reaction

The setting reaction occurs in two steps:
- Amalgamation reaction
- Solid-state reaction
In low-copper amalgam, Ag3Sn (γ) + Hg yields Ag2Hg3 (γ1)+ Sn8Hg2 (γ2).
Unreacted Ag3Sn (γ) and voids are left behind.
In solid state reaction, Sn8Hg(γ2) elimination between Ag-Cu (eutectic) and Sn8Hg (γ2) occurs.
Ag2Hg3 (γ1) and a new phase Cu6Sn5 (η) are created.

Microstructure

Cored structure: Formed from unreacted Ag3Sn (r) and Sn8Hg (82) surrounded by a matrix of Ag2Hg3 (81), with voids.

Properties of dental amalgam phases

Ag3Sn (γ) phase: Strongest & most resistant to corrosion.
Ag2Hg3 (81) phase: Less strong and less resistant to corrosion.
Sn8Hg (82) phase: Weakest and least resistant to corrosion.
Excess mercury reduces strength and corrosion resistance.
Elimination of Sn8Hg (r2) phase improves amalgam properties.

High copper amalgam

Increasing copper content eliminates Sn8Hg (82) phase and improves properties.
Copper content varies from 13-30%.

Admixed high copper amalgam

The copper content increases by mixing silver-copper (Ag-Cu) eutectic alloy and silver-tin Ag3Sn (r) alloy particles.

Setting reaction (steps)

Amalgamation reaction (like low copper).
Solid-state reaction.

Unicompositional high copper amalgam

The amalgam alloy powder is one particle type with a copper content of 13-30%.
Each particle contains Ag3Sn (r) and Cu3Sn (ɛ).

Microstructure (Unicompositional)

Matrix of Ag2Hg3 (γ1) surrounds unreacted particles of [Ag3Sn (γ) + Cu3Sn (ε)].
Cu6Sn5 (η) phase is in a rod-shaped structure, surrounding unreacted particles.
Cu6Sn5 (η) crystals are embedded in the Ag2Hg3 (r1) phase.

Manipulation

The presentation modes of amalgam include tablets & mercury, preproportioned capsules, and powder & mercury.
Amalgam alloy selection depends on factors like particle shape, particle size, zinc content, and copper content.
Proportioning techniques include wet and dry methods (Eam's technique).
Using preproportioned capsules is now common.
Excess mercury results in decreased strength and increased setting expansion/creep.
- Less mercury results in a flawed/friable mix and reduced strength.
- Proper trituration leads to a shiny surface/soft mix with best strength and resistance.
- Over/under trituration negatively affects working time and properties.
Mulling: Rubbing triturated mix into rubber finger-stall.
Condensation: Packing triturated amalgam mix into cavity with increment-by-increment condensation.
Objectives of condensation: Increase restoration adaptation to the cavity wall, reduce mercury content (transfer it to the surface), and create a strong, compact mass.
- Not performed after 3 minutes to avoid reducing strength and adaptation.
Delayed condensation reduces strength, worsens adaptation, and diminishes bonding between increments.
Carving: The cavity is filled; then the top mercury-rich layer is carved,
- Carving objectives: Reproducing tooth anatomy, removing the top mercury-rich layer.
Finishing & polishing: Using finishing burs to finish and polishing with rubber cups and pumice to enhance the surface and increase patient acceptance.
- This is best performed 24 hours after conventional low-copper amalgam and shortly after high-copper amalgam insertion.

Properties

Dimensional changes (immediate and delayed).
- Contraction: Leads to leakage, recurrent caries, hypersensitivity.
- Expansion: Causes tooth fracture or protrusion.
Flow and Creep:
- Flow: Time-dependent plastic deformation during setting (before restoration fully sets).
- Creep: Time-dependent plastic deformation after setting (from below-yield strength stress application).
- Causes: Amalgam's viscoelastic nature, stresses in the mouth, and oral temperature being close to amalgam's softening temperature.
- Significance: Marginal breakdown, gingival irritation, contact area issues.
- Methods for reduction: Using high-copper alloy composition, decreasing mercury content, and proper condensation,
- Strength: Amalgam builds strength slowly, reaching 80% of its final strength within an hour. The immediate compressive strength is more crucial than ultimate strength to prevent fracture due to patient biting. Amalgam is brittle (strong in compression, weak in tension). It's viscoelastic, sensitive to loading rate.
Maximizing strength in an amalgam restoration through:
- Proper cavity preparation (acceptable depth and width to maintain bulk).
- Using a 90-degree cavo-surface angle to prevent thin restoration.
- Rounding sharp line angles to reduce stress concentration.
- Insulating bases to prevent heat transfer.
- Selecting high-copper amalgam, decreasing mercury ratio, and proper trituration.
- Performing appropriate finishing and polishing.
Bond to tooth structure: Dental amalgam is bonded to tooth structure through macro-mechanical retention, with some amalgam bonding systems now in use.
Biological properties: Important aspects include corrosion, thermal properties, and mercury toxicity.
- Corrosion: Results in reduced strength and metallic product release.
  - Reducing corrosion is done by selecting copper-enriched alloy composition, controlling mercury-alloy ratio, ensuring appropriate condensation, and proper surface finishing and polishing.
- Thermal properties: Amalgam conducts heat; an insulating base is essential for deep cavities to prevent thermal sensitivity.
- Mercury toxicity: Pure mercury has a high vapor pressure at room temperature; amalgam is considered highly toxic at 4000 mm/kg of body weight.

Mercury hygiene

Using no-touch technique (e.g., for spills)
Cleaning mercury spills immediately.
Storing amalgam scrap under sodium thiosulfate.
Using water coolant and suction when removing old amalgam restorations.

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Test your knowledge on the intricacies of dental amalgam, including its composition, manufacturing process, and properties. This quiz covers critical aspects such as zinc's role, the types of amalgam, and the effects of heat treatment. Perfect for dental students and professionals seeking to reinforce their understanding.