Dental Restoration: Amalgam Uses and Indications

Why We Use Amalgam

• Inexpensive
• Easy to use
• Proven track record of over 150 years
• Familiarity with the material
• Less allergies than composite resin

Indications and Contraindications for Amalgam Restoration

• Indications: moderate to large restorations, restorations not in highly esthetic areas, restorations with heavy occlusal contacts, restorations that cannot be well isolated, restorations that extend to the root surface, foundations, abutment teeth for removable partial denture, and when cost is a concern for the patient
• Contraindications: esthetically prominent areas of posterior teeth, patients with a history of allergy to mercury or other amalgam components, and small class VI restorations

Alloy Composition

Historical Composition

• GV Black believed amalgam should consist of 67% silver, 27% tin, 5% copper, and 1% zinc

Modern Composition

• Silver and tin are the main components
• Unspecified amounts of other elements such as copper, zinc, gold, and mercury are allowed

Effects of Elements on Amalgam Properties

• Copper: increases expansion, retards setting time, enhances strength
• Tin: decreases flow, increases strength and hardness, reduces setting time
• Zinc: increases plasticity and strength, increases setting time, increases flow, and decreases porosity
• Mercury: activates reaction, increases expansion, increases strength, reduces flow, and reduces creep and marginal breakdown
• Indium: decreases surface tension, reduces amount of mercury necessary, reduces emitted mercury vapor
• Palladium: reduces corrosion, increases luster

Classification of Amalgam Alloys

• Particle geometry and size: irregular (lathe-cut), spherical, admixed
• Copper content: low-copper, high-copper
• Number of particle types: 1, 2
• Zinc content: Zn-containing, Zn-free

Important Knowledge

• Amalgams from lathe-cut powders or admixed powders tend to resist condensation better
• Spherical powders are extremely plastic and require less mercury
• Amalgam alloys may be supplied in pellets, powder, or pills

Basic Structure (Setting Reaction)

• Setting reaction forms different phases, including silver, mercury matrix containing filler particles of silver-tin
• Filler particles can be in various shapes: irregular, spherical, or a combination
• Matrix formed during setting reaction can be gamma 1 (silver-mercury) or gamma 2 (tin-mercury)

Conventional Low-Copper Alloys

• Gamma (γ) phase is the strongest and corrodes the least
• Forms 30-50% of the volume of set amalgam