Dental Amalgam Types

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Questions and Answers

What are the factors that the alloy/Hg ratio depends on in dental amalgam restoration?

The type of amalgam alloy, particle size and shape, and previous heat treatment of the alloy.

What is the minimum wt% of Hg required for spherical alloys?

40 wt%

What is the purpose of trituration in the amalgamation process?

Removing surface oxide film, coating alloy particles with Hg, and supplying energy for the amalgamation reaction.

What is the outcome of the amalgamation reaction on the Y phase?

Decrease in size of remaining unconsumed Y phase. Signup and view all the answers

What happens to the plasticity of the amalgam during the amalgamation reaction?

It decreases due to progressive consumption of Hg. Signup and view all the answers

What are the factors that affect trituration?

Time, speed, and pressure. Signup and view all the answers

What is the result of under-trituration?

Some alloy particles remain covered with oxide film, excess residual Hg, dull and friable mix, and weak, corrodible restoration. Signup and view all the answers

How does a properly triturated mix appear?

Homogeneous, coherent, shiny, plastic, and climbs at the sides of the mortar. Signup and view all the answers

What is the significance of a low creep value in dental amalgam?

It indicates its suitability for extensive preparations involving centric holding areas. Signup and view all the answers

What is the total copper content of the amalgam?

13-30 wt.% Signup and view all the answers

Why is the capsule form of amalgam alloy preferred over other forms?

It provides a standardized pre-weighted amalgam alloy. Signup and view all the answers

What is the consequence of using zinc-containing amalgam in areas of moisture contamination?

It leads to delayed amalgam expansion. Signup and view all the answers

Why is the Y2 phase eliminated in high copper amalgam?

Because it is the most corrodible phase Signup and view all the answers

What is the importance of the alloy/Hg ratio being based on weight rather than volume?

It is due to variations in particle size. Signup and view all the answers

What type of amalgam is used in areas where moisture elimination is impossible?

Zinc free type Signup and view all the answers

What is the main consideration for cavity preparation for amalgam restorations?

Conservative and provides adequate bulk Signup and view all the answers

What is the effect of using less Hg in the proportioning of alloy and mercury?

It results in a non-coherent, friable mix that is difficult to condense and weak and corrodible restoration. Signup and view all the answers

What is the purpose of a definite gingival seat of 1.5-2 mm in depth?

For compound cavities Signup and view all the answers

What is the disadvantage of the wet mix technique (Jorgensen technique)?

It results in more residual Hg, leading to decreased strength, increased expansion, flow, and creep, and tarnish and corrosion. Signup and view all the answers

What is the advantage of the low Hg technique (Eames' technique)?

It minimizes the deleterious effects of residual Hg in the final restoration. Signup and view all the answers

Why is saucering the pulpal floor at the isthmus necessary?

To provide sufficient bulk at the isthmus area Signup and view all the answers

What is the recommended time required for condensation of the amalgam alloy?

3 minutes average time. Signup and view all the answers

What is the advantage of using spherical alloys in pulp capped teeth?

Provides smooth surface and requires less Hg Signup and view all the answers

What is the advantage of high copper amalgam in terms of corrosion resistance?

Greater corrosion resistance Signup and view all the answers

What is the result of rapid Hg consumption and crystallization in amalgam?

It sets fast Signup and view all the answers

What is the characteristic of the mix when it appears homogenous but less plastic and sticks to the sides of the mortar?

Over-trituration Signup and view all the answers

What is the advantage of mechanical trituration over manual trituration?

Standardization of manipulative variables Signup and view all the answers

What is the purpose of mulling in amalgam preparation?

To improve homogeneity and plasticity, and to remove surface oxides Signup and view all the answers

What is the purpose of a dental matrix in compound or complex cavities?

To act as a temporary wall during insertion till hardening of the restorative material Signup and view all the answers

What are the requirements of a dental matrix?

Thin but rigid, easily applied and removed, easily contoured, compatible with the restorative material, and wedged in proximal cavities Signup and view all the answers

What is the objective of condensation in amalgam preparation?

Elimination of excess Hg, decrease of porosity, increase of strength and density, and breaking of alloy particles for further amalgamation reaction Signup and view all the answers

What is the definition of condensation in amalgam preparation?

The process of forcible packing of the fresh amalgam mix into the details of the cavity preparation Signup and view all the answers

What is the primary determinant of the final properties of an amalgam restoration?

Condensation Signup and view all the answers

What is the importance of using only fresh mix during condensation?

To ensure successful condensation, as it should be done within 3 minutes. Signup and view all the answers

What is the direction of the forces of condensation during amalgam restoration?

Toward the cavity details, not to the matrix band. Signup and view all the answers

What is the advantage of mechanical condensation over hand condensation?

Standardization of manipulative variables. Signup and view all the answers

What is the purpose of pre-carve burnishing in amalgam restoration?

To increase adaptation of the condensed amalgam to cavity margins and facilitate carving. Signup and view all the answers

When should carving of the amalgam restoration be done?

After initial setting. Signup and view all the answers

What is the consequence of using a dull carver during carving?

Stress induction, cracks, and disturbances in Hg distribution. Signup and view all the answers

What is the first step in carving a compound restoration?

Initial carving using a carving explorer to reproduce the occlusal embrasures. Signup and view all the answers

Study Notes

High Copper Amalgam

The total copper content of this amalgam is 13-30 wt.%
It eliminates the most corrodible Y2 phase, but if excess Hg is present, Y2 phase will be formed.
High copper amalgam has advantages such as high strength, greater corrosion resistance, and low creep value.

Types of Amalgam

Zinc-containing type (scavenger): used in areas where moisture elimination is impossible, such as partially erupted teeth, deciduous teeth, and subgingival cavities.
Zinc-free type: used in areas where moisture elimination is possible, such as in cavity preparations for amalgam restorations.

Cavity Preparation for Amalgam Restorations

Based on the inherent properties of amalgam (brittle), cavity preparation must be:
- Conservative
- Provides adequate bulk (increased cross-sectional area)
Specific features:
- 90-degree CSA (e.g., reverse curve in the bucco-proximal wall of class II)
- Walls must be parallel or perpendicular to occlusal loads
- Definite gingival seat of 1.5-2 mm in depth for compound cavities
- Rounded internal line angles
- Sufficient bulk at the isthmus area through:
  - Saucerizing the pulpal floor at the isthmus
  - Inclining the axial wall towards the isthmus
  - Rounding the axio-pulpal line angles
Each portion must have its own independent retention and resistance.

Manipulation of Amalgam

Selection of the alloy:
- Spherical alloys provide advantages such as very soft consistency, require less Hg, and provide a smooth surface.
- Indicated in pulp-capped teeth and around pins in pin-retained restorations.
- Not recommended for extensive restorations because it cannot establish better contour and contact areas.
Proportioning:
- Depends on the size of the cavity and the time required for condensation (average time is 3 minutes).
- Alloy/Hg ratio must be based on weight, not volume, due to variation in particle size.
Trituration:
- Definition: the process of mixing together Hg and alloy particles to produce a coherent plastic and homogenous mass of condensable amalgam.
- Objectives:
  - Removing surface oxide film off the alloy particle
  - Coating each alloy particle with Hg
  - Supplying energy for the amalgamation reaction
- Factors affecting trituration:
  - Time (minutes)
  - Speed (rpm)
  - Pressure (F/A)
- Failure to standardize these factors will lead to either under- or over-trituration.
Condensation:
- Definition: the process of forcible packing of the fresh amalgam mix into the details of the cavity preparation.
- Objectives:
 - Elimination of excess Hg
 - Decrease of porosity
 - Increase of strength and density
 - Serves to break some of the alloy particles for further amalgamation reaction
- How to obtain successful condensation:
 - Proper matricing and wedging
 - Only fresh mix should be condensed (< 3 minutes)
 - Forces of condensation should be towards the cavity details, not to the matrix band
 - Incremental condensation
 - Amalgam is carried into the cavity using an amalgam carrier
 - Use of suitably small size condensers of adaptable forms
 - Initial condenser should be small enough to condense into line angles but large enough not to poke holes in the amalgam mass
 - Size of the condenser must be increased in the succeeding layers
 - Slight overfilling (1mm) to ensure that CSA are completely covered
Carving:
- Definition: the procedure by which the anatomical and functional relations of the restored tooth are achieved.
- Timing: after initial setting
- Direction: in any direction except from the restoration to the tooth, because it leads to creation of submargins
- Carver: must be sharp to avoid stress induction, cracks, and disturbances in Hg distribution of the restoration

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