Dental Amalgam: Composition and Properties

Dental Amalgam: Composition, Manufacture, and Properties

• Dental amalgam is a mixture of mercury with another metal or alloy. Mercury's liquid state at room temperature allows for easy mixing.

Mercury's Role in Amalgam

• Mercury is uniquely liquid at room temperature, enabling easy blending with other solid metals. While other metals dissolve in mercury at room temperature, iron is the notable exception.

Composition and Alloying

• The primary components of dental amalgam are silver, mercury, and tin.
• Copper is sometimes added to increase strength.
• Zinc is sometimes added to reduce oxidation.

Amalgam Alloy Manufacturing

• Two primary methods exist:
  • Lathe-cut: Alloy is cast, heated, mechanically grinded, ball-milled, and homogenized.
  • Spherical: Melt is sprayed in an inert atmosphere, forming small spherical particles.

Alloy Powder Characteristics

• Final amalgam alloy is in powdered form.
• Mixed manufacturing techniques (lathe-cut and spherical) are used for improved packing efficiency, reduced mercury use, and enhanced performance.

Lathe-Cut vs. Spherical Alloys (Differences)

• The provided image shows key differences in particle morphology and distribution. Refer to the image for specifics.

Setting Reaction Initiation

• Trituration, vigorous mechanical mixing, initiates the setting reaction. This process combines liquid and powdered components.

Intermetallic Compounds Formed

• Trituration results in the formation of new intermetallic compounds, particularly gamma 1 and gamma 2 phases. Refer to the image associated with this point.

Setting Reaction Steps

• The setting reaction involves the dissolution of silver and tin particles into liquid mercury.
• This process forms a solid matrix of intermetallic phases.
• This reaction continues until the entire mixture solidifies with mercury no longer capable of dissolving further substances.

Trituration Importance

• Appropriate trituration is crucial for proper amalgamation and plastic mix formation.
• Inadequate mixing (under-trituration) results in a crumbly amalgam characterized by incomplete formation of essential phases.
• Excessive mixing (over-trituration), conversely, can lead to excessive shrinkage.

Amalgam Phase Strengths

• The strength of different amalgam phases (gamma, gamma 1, gamma 2) is presented in a ranking - refer to image to see the order of strength.

Amalgams Weakness and Improving Strength

• Gamma 2 is the weakest phase. Reducing its proportion increases the amalgam's strength.

Setting Time and Strength Development

• Amalgam takes more than 24 hours to fully develop its strength.

Amalgam Expansion and Contraction

• Amalgam can contract due to gamma phase dissolution into mercury.
• Amalgam can expand due to gamma 1 and gamma 2 phase crystallisation or sometimes zinc caused expansion.
• These processes may result in marginal gaps or protrusions.

Amalgam's Thermal Properties

• Amalgams possess relatively high thermal diffusivity, making the pulp potentially vulnerable to temperature changes.
• Different thermal expansion coefficients between dentine and amalgam can contribute to microleakage.

Amalgam Corrosion

• Corrosion of amalgam often begins at the amalgam/tooth interface where gamma 2 is more electronegative. This results in dissolution of gamma 2, releasing mercury.

Corrosion Reduction and Benefits

• Polishing the restoration creates a smoother surface, reducing corrosion rate and promoting better sealing, preventing microleakage.

Amalgams Limitations

• Amalgams do not adhere directly to tooth structure.
• They require specific cavity designs, sometimes removing sound tooth tissue.
• Amalgams have poor aesthetics, typically making fillings appear less natural compared to other materials.
• Amalgam can generate galvanic effects between different materials.
• High thermal diffusivity may cause thermal sensitivity.

Creep in Dental Restorations

• Creep is the time-dependent deformation of a material under load that does not recover fully upon load removal.
• In amalgam, a higher gamma 2 concentration is associated with a greater susceptibility to creep.
• This can lead to protrusion, cavity weakening, and fracture.

Reducing Creep

• Using high-copper amalgams can help to decrease creep and corrosion due to specific metallic characteristics.

Amalgam Alloy Mixture Formulation Equation

• The image provides the equation for the particular dispersion modified copper-enriched amalgam; refer to it for the details.

Advantages of High-Copper Amalgam

• Higher compressive strength.
• Quicker development of final strength.
• Lower creep tendencies.
• Less susceptibility to corrosion.

Amalgam Restoration Procedure Steps

• Detailed steps to set amalgam fillings are outlined.

Cavity Preparation Considerations

• Cavity preparation should prevent unsupported enamel remnants.
• A rounded shape is preferred over a wedge-shaped design to distribute stress efficiently.
• Ensure the preparation is adequately designed and not too close to the pulp.

Amalgam Condensation Techniques

• Amalgam condensation techniques focus on minimizing excess mercury, ensuring no voids, and establishing a correct marginal seal.
• Amalgam is condensed in small increments and may even require overfilling.

Condensation Pressure Differences

• Spherical amalgams generally require less condensation pressure.

Carving Amalgam: Time and Techniques

• Amalgam carving typically takes 2-3 minutes. Excessive pressure should be avoided.

Amalgam Surface Quality Comparison

• Spherical amalgams are often associated with improved surface characteristics relative to lathe-cut amalgams. Refer to diagrams if available to see visual information.

Environmental Concerns

• Images displayed for environmental concerns associated with mercury use.

Health Concerns

• Images displayed for health concerns associated with mercury use.

Amalgam Removal Safety

• Safety measures for amalgam removal address both patient and operator exposure. Refer specifically to the provided images for guidelines.

Amalgam Use Discouragement

• Amalgams are discouraged in specific situations, particularly for deciduous teeth, minors, pregnant women, and those breast feeding.

Explore the fascinating world of dental amalgam, focusing on its composition, manufacturing processes, and important properties. This quiz covers key components such as mercury, silver, and copper, as well as methods like lathe-cut and spherical alloy production. Test your knowledge on this essential dental material!