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Questions and Answers

Which type of dental amalgam demonstrates higher compressive strength?

  • Low copper alloy
  • High copper alloy (correct)
  • Neither type has compressive strength
  • Both types equally

What is one consequence of excessive corrosion in dental amalgam?

  • Decreased porosity
  • Enhanced marginal integrity
  • Increased dimensional stability
  • Loss of strength (correct)

Which property is lower in high copper alloys compared to low copper alloys?

  • Tensile strength
  • Marginal integrity
  • Creep and flow (correct)
  • Compressive strength

Which of the following statements is true regarding the dimensional changes of low copper alloy amalgam?

<p>It experiences more dimensional changes. (B)</p> Signup and view all the answers

What aspect of high copper alloy amalgam indicates its superior durability compared to low copper alloy?

<p>Less tarnish and corrosion (B)</p> Signup and view all the answers

What is the maximum percentage of copper in a low copper alloy?

<p>6% (A)</p> Signup and view all the answers

Which component in dental amalgam primarily increases strength and tarnish resistance?

<p>Silver (Ag) (C)</p> Signup and view all the answers

In a high copper amalgam, which phase is considered the weakest?

<p>Gamma 2 (A)</p> Signup and view all the answers

What is the purpose of zinc in dental amalgam?

<p>To prevent oxidization of other metals (C)</p> Signup and view all the answers

Which property indicates a material's ability to withstand forces directed toward it?

<p>Compressive strength (C)</p> Signup and view all the answers

What type of amalgam reacts with both mercury and copper in its composition?

<p>High copper amalgam (A)</p> Signup and view all the answers

Which property is directly associated with the dimensional stability of dental amalgams?

<p>Creep (D)</p> Signup and view all the answers

What defines a zinc-free alloy in dental applications?

<p>Contains 0.01% or less Zn (B)</p> Signup and view all the answers

What is the range of compressive strength for amalgam after 7 days?

<p>300-500 Mpa (C)</p> Signup and view all the answers

Which type of amalgam exhibits the highest early tensile strength?

<p>High copper amalgam (B)</p> Signup and view all the answers

How does temperature affect the strength of amalgam?

<p>It decreases strength by 15% from root to mouth temperature. (D)</p> Signup and view all the answers

What is the effect of high mercury content in amalgam?

<p>It can decrease strength by up to 50%. (B)</p> Signup and view all the answers

What happens to amalgam if it is under-triturated?

<p>It negatively affects the amalgam strength. (B)</p> Signup and view all the answers

What is the modulus of elasticity range for amalgam?

<p>20-50 Gpa (A)</p> Signup and view all the answers

Which amalgam type requires more condensation for higher compressive strength?

<p>Lathe-cut alloy (C)</p> Signup and view all the answers

What defines creep in dental amalgam?

<p>Time-dependent plastic deformation under static load. (A)</p> Signup and view all the answers

Flashcards

Low copper amalgam setting reaction

AgSn reacts with Hg to form AgSn, AgHg, and SnHg phases, with some unreacted phases.

High copper amalgam setting reaction

AgSn, Ag-Cu react with Hg which create AgSn, AgHg, SnHg & Ag-Cu phases with eutectic and unreacted phases.

Low copper amalgam composition

Contains less than 6% copper.

High copper amalgam composition

Contains more than 12% copper.

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Dental Amalgam Creep

A slow, permanent deformation under sustained stress.

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Dental Amalgam Tarnish

Surface discoloration or dulling of the amalgam.

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Compressive Strength (Amalgam)

Amalgam's ability to withstand forces pushing inward.

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Zinc-containing alloy

Any alloy containing more than 0.01% zinc.

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What is corrosion?

Corrosion is the breakdown of a metal's surface caused by chemical or electrochemical reactions with its environment. It can lead to a weaker, more porous material and potentially release metal particles.

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How does corrosion impact dental amalgam?

Amalgam corrosion weakens the filling, making it more porous and less effective. This can cause leakage, weakening, and even metal release into the mouth.

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What is the effect of corrosion on amalgam strength?

Corrosion reduces the strength of amalgam, leading to potential cracking and failure of the filling.

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High copper vs. low copper: Corrosion?

High copper amalgams resist corrosion better than low copper amalgams. This is because the copper reacts with tin to form a protective layer, reducing the amount of mercury which can be released by corrosion.

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How can corrosion lead to metal release?

Corrosion weakens the metal to the point it can release metal particles into the surrounding environment, potentially posing health concerns.

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What is the compressive strength of amalgam?

Amalgam has a high compressive strength, ranging from 300-500 MPa after 7 days. This strength depends on the type of amalgam used, with low copper amalgam having the lowest compressive strength.

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What is the tensile strength of amalgam?

Amalgam is weak under tensile forces, meaning it doesn't handle stretching well. Its tensile strength ranges from 48-60 MPa after 7 days, with low copper amalgam having the lowest tensile strength. High copper amalgam exhibits higher initial tensile strength within the first 15 minutes, making it better at resisting fractures.

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How does temperature affect amalgam strength?

Temperature significantly affects amalgam strength. It loses approximately 15% of its strength when the temperature increases from root temperature to oral temperature. It loses 50% of its strength when the temperature reaches 60°C (140°F), like when consuming hot beverages.

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Does mercury content influence amalgam's strength?

Yes, high mercury content can decrease amalgam strength by up to 50%. It's best to use low mercury alloys. However, too little mercury can produce a rough, pitted surface.

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How does trituration affect amalgam strength?

Trituration, the mixing process, affects amalgam strength depending on the type of alloy, trituration time, and amalgameter speed. Under- or over-trituration weakens the amalgam, even with high or low copper content.

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What's the role of condensation in amalgam strength?

Condensation plays a crucial role. Lathe-cut alloys require more condensation for higher compressive strength. Spherical alloys need lighter condensation. It's like packing a suitcase - too tight or too loose, and things won't fit right!

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What is 'creep' in the context of amalgam?

Creep is a time-dependent plastic deformation of amalgam under static load. It's like a gradual sag or settling over time. Creep is measured after setting and can cause the amalgam to flow towards the margins, potentially causing it to protrude.

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How does amalgam's modulus of elasticity compare to other dental materials?

The modulus of elasticity measures a material's stiffness. Amalgam has a modulus between 20-50 GPa, making it stiffer than dentin (15-20 GPa) and composite (17-22 GPa) but less stiff than enamel (50-80 GPa). High copper amalgam is generally stiffer than low copper amalgam.

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Study Notes

Operative Dentistry I: Amalgam Restoration and Manipulation I

  • 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

  • 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
  • According to Copper Content:
    • Low copper alloy: Less than 6% copper
    • High copper alloy: More than 12% copper
  • 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

  • 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).
  • 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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