Dental Amalgam Properties and Classification

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Questions and Answers

What happens when zinc-containing amalgam is contaminated with water during trituration?

It loses all plasticity.

It may cause delayed expansion. (correct)

It creates a smooth surface.

It hardens immediately.

What is the main cause of secondary expansion in zinc-containing amalgam?

High mercury content.

Under-trituration.

Moisture contamination. (correct)

Poor condensation technique.

What type of strength does hardened amalgam possess mostly?

Balanced shear strength.

High tensile strength.

Good compressive strength. (correct)

High bending strength.

Which factor does NOT affect the strength of amalgam?

Dental pulp condition. Signup and view all the answers

How does high condensation pressure impact amalgam strength?

It enhances compressive strength. Signup and view all the answers

What effect does excess mercury in an amalgam mix have?

It reduces the overall strength. Signup and view all the answers

What causes porosity in amalgam?

Insertion of too large increments. Signup and view all the answers

When does amalgam typically gain strength?

It increases strength with time. Signup and view all the answers

What is the primary advantage of dental amalgam?

It has been used successfully for over a century. Signup and view all the answers

What characterizes high copper alloys in dental amalgam?

Contain more than 13-30% copper. Signup and view all the answers

What is a result of contraction in dental amalgam?

Potential gaps between the restoration and tooth. Signup and view all the answers

What factor does NOT favor contraction of amalgam?

Longer trituration times. Signup and view all the answers

How does modern amalgam generally behave in comparison to older amalgams?

Modern amalgams show a net contraction. Signup and view all the answers

What is the initial dimensional change that occurs after the tirturation of amalgam?

Contraction only. Signup and view all the answers

What is a characteristic of lathe cut alloys in dental amalgam?

They have an irregular shape. Signup and view all the answers

Which of the following is NOT a factor influencing dimensional change in amalgam?

The color of the restoration. Signup and view all the answers

What should be used to wash skin contact with mercury?

Soap and water Signup and view all the answers

What is recommended during the removal of old mercury fillings?

Use water spray and high suction Signup and view all the answers

What is the most accurate method for dispensing amalgam?

Using pre-proportioned capsules Signup and view all the answers

Which type of amalgam typically requires a shorter mixing time?

Spherical alloys Signup and view all the answers

What can result from under mixing amalgam?

Weaker mechanical properties Signup and view all the answers

Why are handheld dispensers for alloy and mercury considered unreliable?

They do not allow for accurate measurements Signup and view all the answers

What ratio of mercury to alloy is typical for certain amalgams?

Less than 1:1 Signup and view all the answers

What is an advantage of mechanical mixing compared to hand mixing?

Standardized procedure Signup and view all the answers

What should patients be cautioned against doing for at least 8 hours after placement?

Biting too hard Signup and view all the answers

What is creep in dental amalgam primarily related to?

Marginal breakdown of low copper amalgam Signup and view all the answers

Which factor can help reduce the creep rate of dental amalgam?

Trituration and condensation timing Signup and view all the answers

What is the primary effect of tarnish on dental amalgam?

Causes loss of luster without changing mechanical properties Signup and view all the answers

What condition can excessive corrosion in dental amalgam lead to?

Increased porosity and loss of strength Signup and view all the answers

Which factor is associated with higher creep rates in dental amalgam?

Y2 phase presence Signup and view all the answers

What condition exacerbates tarnish in dental amalgam?

Rough surfaces and moisture contamination Signup and view all the answers

What happens to amalgam when the creep rate is above 3%?

It leads to increased marginal deterioration Signup and view all the answers

What effect does high residual mercury have on materials?

Increases corrosion Signup and view all the answers

Why should mixed high copper and low copper amalgams be avoided?

They increase galvanic corrosion Signup and view all the answers

What is one method to reduce corrosion of amalgam?

Smooth and polish the restoration Signup and view all the answers

What condition makes low copper amalgam more susceptible to corrosion?

Greater y2 content Signup and view all the answers

What is a potential health risk associated with mercury during dental procedures?

It has a cumulative toxic effect Signup and view all the answers

What can enhance the thermal properties of amalgam fillings?

Using a liner with a low thermal diffusivity Signup and view all the answers

Which statement about mercury vapors during dental procedures is correct?

They can be absorbed through the skin Signup and view all the answers

What precaution should be taken in a dental clinic regarding mercury?

Ventilate the clinic well Signup and view all the answers

What characterizes under triturated amalgam?

It appears as a solid mass without luster. Signup and view all the answers

What is the primary aim of the condensation process in amalgam restoration?

To adapt the amalgam mass to the cavity walls. Signup and view all the answers

Which type of amalgam requires higher mercury content due to its shape?

Irregularly shaped alloys Signup and view all the answers

What should be used for condensation when working with small irregularly shaped alloys?

Small tip condensers. Signup and view all the answers

What is the effect of increasing condensation pressure on amalgam?

Increases compressive strength. Signup and view all the answers

What is the purpose of carving in amalgam restoration?

To reproduce the tooth anatomy. Signup and view all the answers

What should NOT be done during the polishing stage of amalgam restoration?

Increase the roughness of the surface. Signup and view all the answers

Why are ultrasonic condensers not recommended during condensation?

They increase mercury vapor levels. Signup and view all the answers

Study Notes

Dental Amalgam

Dental amalgam is an alloy created from mixing liquid mercury with solid silver, tin, copper, and zinc particles.
It's been used for over a century as a restorative material for tooth decay, primarily in posterior teeth.
Amalgam is supplied as bulk powder and mercury, or as an alloy and mercury mixture in disposable capsules for use in an amalgamator machine.

Amalgam Alloy Classification

Based on Copper Content:
- Low copper alloys contain less than 6% copper (conventional).
- High copper alloys contain 13-30% copper.
Based on Zinc Content:
- Zinc-containing alloys contain over 0.01% zinc.
- Zinc-free alloys contain less than 0.01% zinc.
Based on Alloy Particle Shape:
- Lathe cut alloys have irregular shapes.
- Spherical alloys have spherical shapes.
- Mixtures of lathe cut and spherical alloys are also used.

Amalgam Properties

Dimensional Change: Amalgam generally expands or contracts slightly during setting. Expansion can cause post-placement sensitivity or protrusion from the cavity. Contraction can lead to gaps between restoration and tooth, potentially causing leakage and recurrent decay. Initial contraction usually occurs within the first 20 minutes after trituration.
Factors Favoring Contraction:
- Low mercury/alloy ratio
- Higher condensation pressure
- Smaller particle size
- Longer trituration times
Factors Favoring Expansion:
- Presence of Zinc in alloy mixture
- Moisture contamination (delayed/secondary expansion)

Amalgam Strength

Hardened amalgam has good compressive strength but low tensile or bending strength.
Cavity design should minimize tension and shear forces
Factors affecting strength include proper trituration, mercury/alloy ratio, and condensation pressure in the alloy.

Amalgam Porosity

Porosity (voids) lessen amalgam strength.
Factors contributing to porosity include low and high Hg/alloy ratio, insufficient condensation, and irregularities in alloy particle shape.

Rate of Hardening

Amalgam strength increases over time.
Patients should avoid biting hard on restorations for at least 8 hours following placement to allow strength gain.

Amalgam Creep

Creep is time-dependent plastic deformation in amalgam.
Creep is related to marginal breakdown in low-copper amalgam.
Higher creep rates lead to greater marginal deterioration.
Low copper amalgam creep: 0.8-8.0%
High copper amalgam creep: 0.4-0.1%.

Amalgam Tarnish and Corrosion

Tarnish is a loss of luster due to surface coating.
Corrosion is the progressive destruction of a metal due to chemical/electrochemical reactions.
Factors affecting tarnish and corrosion include high mercury residue, dissimilar metal contact (galvanic corrosion), rough surfaces, and moisture.
Corrosion is worsened by high sulfur intake.
Corrosion products can accumulate at the restoration-tooth interface. Techniques such as smoothing and polishing, correct Hg/alloy ratio, and proper manipulation can help reduce corrosion.

Amalgam Thermal Properties

Amalgam has high thermal diffusivity.
Insulating cavity linings are often used in large cavities to mitigate potential thermal sensitivity.

Amalgam Biological Properties

Certain mercury compounds can have harmful effects on the central nervous system.
Properly handled dental amalgam is generally considered safe for restorative use.
Mercury is toxic, and exposure to mercury vapors or contact should be avoided. Ventilation and safety precautions are necessary for handling amalgam.

Amalgams Manipulation

Proportioning and Dispensers: Using pre-measured tablets or capsules is recommended to ensure accurate proportions of alloy and mercury. Dispensers by volume are less reliable due to inconsistent packing of powder and mercury.
Triturating (Mixing): Using hand mixing (mortar and pestle) or mechanical amalgamators can help achieve the desired mix. A more standardized procedure with mechanical triturating is preferred.
Condensation: This involves compacting the amalgam into the cavity walls. Manual and Mechanical techniques are available and effective methods for ensuring adequate condensation are required.
Carving: Carving is the process of shaping the amalgam to match the tooth anatomy. This step is done after condensation.
Polishing: This is performed to minimize corrosion and plaque adhesion. Polishing should be done at least 24 hours after condensation.

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Description

Explore the various properties and classifications of dental amalgam, an important material used in restorative dentistry. This quiz covers its composition, copper and zinc content, and the different shapes of amalgam particles. Test your knowledge on this significant topic in dental care.