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Questions and Answers
Which type of dental amalgam demonstrates higher compressive strength?
Which type of dental amalgam demonstrates higher compressive strength?
What is one consequence of excessive corrosion in dental amalgam?
What is one consequence of excessive corrosion in dental amalgam?
Which property is lower in high copper alloys compared to low copper alloys?
Which property is lower in high copper alloys compared to low copper alloys?
Which of the following statements is true regarding the dimensional changes of low copper alloy amalgam?
Which of the following statements is true regarding the dimensional changes of low copper alloy amalgam?
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What aspect of high copper alloy amalgam indicates its superior durability compared to low copper alloy?
What aspect of high copper alloy amalgam indicates its superior durability compared to low copper alloy?
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What is the maximum percentage of copper in a low copper alloy?
What is the maximum percentage of copper in a low copper alloy?
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Which component in dental amalgam primarily increases strength and tarnish resistance?
Which component in dental amalgam primarily increases strength and tarnish resistance?
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In a high copper amalgam, which phase is considered the weakest?
In a high copper amalgam, which phase is considered the weakest?
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What is the purpose of zinc in dental amalgam?
What is the purpose of zinc in dental amalgam?
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Which property indicates a material's ability to withstand forces directed toward it?
Which property indicates a material's ability to withstand forces directed toward it?
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What type of amalgam reacts with both mercury and copper in its composition?
What type of amalgam reacts with both mercury and copper in its composition?
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Which property is directly associated with the dimensional stability of dental amalgams?
Which property is directly associated with the dimensional stability of dental amalgams?
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What defines a zinc-free alloy in dental applications?
What defines a zinc-free alloy in dental applications?
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What is the range of compressive strength for amalgam after 7 days?
What is the range of compressive strength for amalgam after 7 days?
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Which type of amalgam exhibits the highest early tensile strength?
Which type of amalgam exhibits the highest early tensile strength?
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How does temperature affect the strength of amalgam?
How does temperature affect the strength of amalgam?
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What is the effect of high mercury content in amalgam?
What is the effect of high mercury content in amalgam?
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What happens to amalgam if it is under-triturated?
What happens to amalgam if it is under-triturated?
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What is the modulus of elasticity range for amalgam?
What is the modulus of elasticity range for amalgam?
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Which amalgam type requires more condensation for higher compressive strength?
Which amalgam type requires more condensation for higher compressive strength?
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What defines creep in dental amalgam?
What defines creep in dental amalgam?
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Study Notes
Operative Dentistry I: Amalgam Restoration and Manipulation I
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Lecture Objectives:
- Define dental amalgam restoration
- List advantages, disadvantages, indications, and contraindications of amalgam restoration
- Identify dental amalgam classifications
- Identify dental amalgam composition
- Explain dental amalgam setting reaction
- Describe dental amalgam properties
Introduction to Dental Amalgam
- Definition: A metallic restorative material composed of a mixture of silver-tin-copper alloy and mercury
- Application: The unset mixture is pressed (condensed) into a prepared tooth cavity and contoured to restore the tooth's form and function
Advantages of Amalgam Restoration
- Ease of use
- High strength
- Excellent wear resistance
- Favorable long-term clinical research results
- Low cost
Disadvantages of Amalgam Restoration
- Non-esthetic
- Less conservative (requires more tooth removal during preparation)
- Non-insulating
- More difficult tooth preparation
- Environmental concern
Indications for Amalgam Restoration
- Posterior teeth restorations
- Large cavities
- Areas with limited moisture control
- Core build-ups for crowns
Contraindications for Amalgam Restoration
- Esthetic areas (anterior teeth)
- Mercury-sensitive patients
- Small cavities
- If composite restoration is a better conservative option
Amalgam Classification
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According to Particle Shape:
- Spherical alloy: Requires less condensation, easy carving, improper proximal contact, used in class I cavities
- Lathe-cut alloy: Requires more condensation, difficult carving, proper proximal contact, used in class II cavities
- Admix alloy: Combines advantages of spherical and lathe-cut alloys
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According to Copper Content:
- Low copper alloy: Less than 6% copper
- High copper alloy: More than 12% copper
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According to Zinc Content:
- Zinc-containing alloy: More than 0.01% zinc
- Zinc-free alloy: 0.01% or less zinc
Dental Amalgam Composition
- Silver (Ag): Increases strength, prevents tarnish and corrosion
- Tin (Sn): Decreases strength, increases flow and creep
- Copper (Cu): Increases strength, prevents tarnish and corrosion
- Zinc (Zn): Prevents oxidation of other metals, improves strength and creep resistance
Dental Amalgam Setting Reaction
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Low Copper Amalgam (Conventional): Silver-tin + mercury → silver-tin, silver-mercury, tin-mercury
- Forms unreacted gamma (γ) phase, gamma 1 (γ1) phase (strongest), and gamma 2 (γ2) phase (weakest).
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High Copper Amalgam: AgSn + Ag-Cu + Hg → Silver-tin , silver-mercury, tin-mercury Silver-copper
- Eutectic formation with additional phases
Dental Amalgam Properties
- Compressive Strength: Ability to withstand compression; high in amalgam, varies based on amalgam type
- Tensile Strength: Ability to withstand pulling or stretching forces; low in amalgam, high early strength
- Modulus of Elasticity: Measure of material stiffness; varies, high in high copper amalgam
- Creep & Flow: Time-dependent plastic deformation; flows during setting and afterward; high in low copper amalgam
- Dimensional Changes: Changes in shape and size with temperature or chemical reaction; high in amalgam
- Tarnish & Corrosion: Discoloration and degradation of the surface; impacted by environmental factors, like moisture, food, and oral hygiene; impacted by amalgam composition and design
- Factors Affecting Amalgam Strength: Temperature, mercury content, trituration, condensation
Factors Affecting Amalgam Creep
- Composition: Y2 presence in low copper amalgam increases creep
- Manipulation: Proper condensation and trituration time in high copper amalgam reduces creep
Factors Affecting Amalgam Dimensional Changes
- Mercury Content: High mercury results in high expansion
- Trituration: Under-trituration causes expansion; over-trituration causes contraction
- Condensation: Less condensation pressure leads to expansion
Dental Amalgam Tarnish & Corrosion
- Tarnish: Discoloration due to surface reactions with chemicals, poor oral hygiene, or acidic foods.
- Corrosion: Chemical or electrolytic process that dissolves the amalgam surface, causing deterioration; can lead to mechanical failure.
- Excessive Corrosion: Can lead to increased porosity, reduced marginal integrity, loss of strength, and release of metallic products in the oral environment
Amalgam Self Sealing Ability
- Amalgam has self-sealing ability due to the filling of the interface gap by corrosion products forming.
- Creep expansion is a critical factor in this process.
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