Dental Amalgam Chapter 5 Quiz

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Questions and Answers

What percentage of copper is found in high copper amalgam alloys?

No copper

Less than 6%

More than 6% (correct)

Exactly 6%

Which metal in dental amalgam primarily increases strength and decreases creep?

Mercury

Zinc

Tin

Copper (correct)

Which property of amalgam is primarily decreased by silver content?

Workability

Strength

Setting time

Creep (correct)

What role does zinc play in dental amalgam?

Prevents oxidation Signup and view all the answers

Which corrosion product is associated with silver in dental amalgam?

AgCl and AgS Signup and view all the answers

How does tin affect the setting time of an amalgam restoration?

Increases setting time Signup and view all the answers

What is a primary advantage of using dental amalgam as a restorative material?

High compressive strength and hardness Signup and view all the answers

What effect does mercury have on the properties of dental amalgam?

Decreases strength if in excess Signup and view all the answers

What is the main constituent of dental amalgam?

Mercury Signup and view all the answers

What is the approximate percentage of liquid mercury in dental amalgam?

43 to 54% Signup and view all the answers

What is formed during the amalgamation reaction?

A hard restorative material Signup and view all the answers

Why has dental amalgam remained popular for over 150 years?

It offers ease of manipulation and low cost Signup and view all the answers

What kind of reaction occurs when mercury is mixed with an alloy in dental amalgam?

Amalgamation reaction Signup and view all the answers

Which of the following elements is NOT typically found in the alloy powder used for dental amalgam?

Aluminum Signup and view all the answers

What color is dental amalgam typically described as?

Silvery-gray Signup and view all the answers

What is a primary concern regarding the use of dental amalgam?

Mercury toxicity Signup and view all the answers

What is the term for the change in volume of amalgam due to temperature changes?

Dimensional change Signup and view all the answers

What percentage of strength does amalgam reach after one hour of placement?

40 to 60% Signup and view all the answers

What is a key disadvantage of using dental amalgam?

Aesthetics Signup and view all the answers

How does creep affect the properties of amalgam?

It leads to gradual dimensional change under load. Signup and view all the answers

What can happen if an amalgam filling expands excessively?

It could protrude from the cavity. Signup and view all the answers

What phenomenon is characterized by a chemical reaction between amalgam and its environment that affects only the surface?

Tarnish Signup and view all the answers

What effect does contact with a gold restoration have on an amalgam filling?

Accelerates corrosion Signup and view all the answers

What is considered an objectionable effect of dental amalgam related to its appearance?

Amalgam tattoo Signup and view all the answers

How does the coefficient of thermal expansion for amalgam compare to that of dentine?

It is about three times greater. Signup and view all the answers

What potential issue can arise from the thermal expansion of amalgam?

Microleakage around the fillings. Signup and view all the answers

What is the most critical responsibility of the dental specialist with regard to amalgam?

Correct preparation and use of amalgam. Signup and view all the answers

What happens if the amalgam mix contains greater quantities of mercury?

It becomes ‘wetter’ and is used with hand mixing. Signup and view all the answers

What is the optimal final mercury content in amalgam for lathe-cut materials?

About 45%. Signup and view all the answers

What is a known effect of certain mercury compounds on human health?

They can harm the central nervous system. Signup and view all the answers

What does trituration refer to in the manipulation of amalgam?

Mixing the alloy with mercury. Signup and view all the answers

What allergic reaction is usually associated with amalgam fillings?

Contact dermatitis. Signup and view all the answers

What is the main advantage of using a mechanical amalgamator for trituration?

It allows for a more uniform and reproducible mix. Signup and view all the answers

What is the optimal mercury content in set amalgam?

44-48% Signup and view all the answers

What is the most significant risk if condensation is delayed after trituration?

It becomes too hard to carve and may chip. Signup and view all the answers

Which of the following instruments is primarily used for condensing amalgam?

Amalgam condenser Signup and view all the answers

Why is polishing of amalgam fillings typically delayed for 24 hours?

To allow for the restoration to harden and gain mechanical strength. Signup and view all the answers

Which factor is crucial for achieving optimal mechanical properties in set amalgam?

Adequate adaptation to the cavity. Signup and view all the answers

What should be done soon after condensing amalgam?

Carve away the surface layer rich in mercury. Signup and view all the answers

What generally requires lower forces during the condensation of amalgam?

Spherical particle amalgams. Signup and view all the answers

Study Notes

Introduction to Dental Amalgam

Dental amalgam has been a standard restorative material for over 150 years, primarily for posterior restorations.
Its popularity is due to its ease of manipulation, cost-effectiveness, and longevity.
Although there are concerns regarding mercury toxicity, dental amalgam is generally considered to present an acceptable risk-to-benefit ratio when used properly.

Composition of Dental Amalgam

Dental amalgam consists of mercury combined with an alloy of silver, tin, copper, and sometimes zinc or other trace metals.
An amalgamation reaction occurs when the alloy is mixed with mercury, resulting in a hard, silvery-gray restorative material.

Alloy Composition and Properties

Common composition for conventional amalgam alloy includes:
- Silver (Ag): 40-60%
- Tin (Sn): 27-30%
- Copper (Cu): 13-30%
- Zinc (Zn): up to 2%
- Mercury (Hg): 3%
Each metal serves distinct roles:
- Silver enhances strength and expansion, minimizes creep.
- Tin increases reactivity and corrosion but decreases strength.
- Copper improves strength and corrosion resistance.
- Zinc adds plasticity and prevents oxidation.

Classification of Amalgam

Amalgam can be classified based on several criteria:
- Number of alloyed metals
- Shape of the particles
- Copper content: low (<6%) vs. high (>6%)
- Zinc content: zinc-containing (>0.01%) vs. zinc-free (<0.01%)
- Unmixed vs. admixed types

Advantages and Disadvantages

Advantages:
- High compressive strength and durability.
- Ease of handling and manipulation.
- Excellent wear resistance and distinction from tooth structure.
- Cost-effective restoration option.
Disadvantages:
- Aesthetic concerns due to silver color.
- Potential mercury exposure and related health hazards.
- Possible occurrence of amalgam tattoos and lack of insulation.

Properties Affecting Amalgam Restorations

Dimensional Changes: Proper dimensioning is critical; large contractions can lead to gaps, while expansions may cause sensitivity.
Strength: Amalgam gains strength over time. It reaches 90% strength within 24 hours and is weaker shortly after placement.
Creep: Amalgam may undergo plastic deformation under stress.
Corrosion & Tarnish: Corrosion affects mechanical properties and is accelerated in contact with other metals; tarnish primarily affects the surface.
Thermal Properties: Amalgam has a higher thermal conductivity than dentine, leading to potential issues with microleakage.
Biological Properties: Mercury compounds may impact the nervous system, and allergic reactions might occur.

Manipulation of Amalgam

Key steps for amalgam manipulation include:
- Proportioning & Dispensing: Ratio of alloy to mercury typically ranges from 5:8 to 10:8. Optimal final mercury content is under 50%.
- Trituration: Mixing can be done mechanically or manually, with mechanical being more common for consistency and efficiency.
- Condensation: Proper condensation ensures ideal adaptation within the cavity and reduces porosity.
- Carving: Carving after condensation must be timely to avoid hardening.
- Polishing: Polishing is performed after achieving adequate strength to enhance aesthetics and resistance to corrosion; usually requires a 24-hour delay post-placement.

Conclusion

The dental professional is responsible for the correct use and preparation of amalgam to ensure quality restorations.
Proper handling and preparation are critical to avoiding faulty restorations that may jeopardize tooth integrity.

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Description

This quiz covers the key concepts of dental amalgam, focusing on its history, uses, and safety considerations. Explore the reasons behind its long-standing popularity and the current debates regarding mercury toxicity. Test your understanding of dental therapeutics and its implications.