Amalgam Flashcards
(21 cards)
What is dental amalgam?
An alloy made by mixing Hg with Ag dental amalgam alloy
Often referred to as silver paste.
What percentage of silver is typically found in dental amalgam?
48-70%
Silver increases expansion, retards setting time, enhances strength, decreases flow, and resists tarnish/corrosion.
What role does copper play in dental amalgam?
6-28% copper reduces setting time, increases expansion, and increases strength and hardness
Copper unites with Hg with difficulty and tarnishes readily.
What is the function of tin in dental amalgam?
10-17% tin retards setting time, improves plasticity, and reduces expansion
Tin unites readily with Hg and increases flow.
What is the role of zinc in dental amalgam?
0-0.01% zinc causes expansion, increases setting time, and inhibits oxidation
Zinc combines readily with Hg and decreases porosity.
Name two classifications of dental amalgam based on particle geometry.
- Lathe-cut
- Spherical
- Admix
What is micro leakage in dental amalgam?
The tendency of dental amalgam to minimize micro leakage if the restoration is properly inserted
Leakage decreases as restoration ages due to the formation of corrosion products.
What is creep in dental amalgam?
Progressive permanent deformation of set amalgam under dynamic loading
Low copper amalgam exhibits 2.5% creep; high copper amalgam exhibits 0.2% creep.
True or False: Dental amalgam has high tensile and shear strength.
False
Amalgam exhibits high compressive strength but poor tensile and shear strength.
What is the significance of the alloy-mercury ratio in dental amalgam?
Irregular particles pack poorly and require a larger amount of Hg (50%-60%)
Pre-capsulated amalgam (spherical) has 42%-45% mercury.
What is trituration in the context of dental amalgam?
The process of manual mixing of alloy with Hg
This can be done by hand or using a mechanical amalgamator.
What defines the gamma phase in dental amalgam?
The silver-tin phase composed of unreacted alloy particles.
List two indications for using dental amalgam.
- Class I and class II cavities
- Core build-up material
Name one contraindication for using dental amalgam.
Anterior teeth where esthetics is a prime concern.
What is one advantage of dental amalgam?
Ease of use and manipulation.
What is one disadvantage of dental amalgam?
Unnatural appearance (non esthetic).
Fill in the blank: Amalgam exhibits _______ strength.
high compressive
What is the effect of mercury on the strength of amalgam?
Increase in mercury decreases the strength of amalgam.
What is the modulus of elasticity (MOE) of high copper amalgam?
55 GPa
This is close to enamel and increases longevity of amalgam restoration.
What are the thermal properties of dental amalgam?
Amalgam is a good thermal conductor
Pulp should be protected with varnish, liners, or bases.
What is the chemical reaction involved in dental amalgam formation?
Mercury + Silver-Tin = Silver-Tin phase + Silver-mercury phase + Tin-mercury phase.
