Dental Amalgam Overview and Analysis

Dental Amalgam Overview

• Amalgam is an alloy combining liquid mercury with solid metal particles (silver, tin, copper, sometimes zinc, palladium, indium, selenium)
• Used as a dental restoration material for over a century, due to low cost, ease of application, strength, and durability
• Concerns regarding aesthetics, environmental pollution, mercury toxicity, and the availability of composite materials have diminished its popularity
• Commonly used for posterior restorations and large foundation restorations, sometimes for cores with crowns.

Advantages of Dental Amalgam

• Reasonably easy to insert, not a sensitive technique
• Maintains anatomical form
• Provides adequate resistance to fractures (strength)
• Prevents marginal leakage over time
• Suitable for stress-bearing areas
• Relatively long service life (durability)
• Cost-effective

Disadvantages of Dental Amalgam

• Silver color does not match tooth structure
• Brittle, prone to corrosion and galvanic action
• Can exhibit marginal breakdown
• Does not retain weakened tooth structure
• Regulatory concerns regarding disposal in wastewater

Composition of Dental Amalgam

• Primarily consists of silver and tin, with smaller amounts of copper, zinc, and trace elements (gold, palladium, indium, selenium).
• Various types exist based on copper content (low copper, high copper) and zinc content: zinc containing and zinc free.
• Specific percentages of silver, tin, copper, and zinc vary by amalgam type (e.g., low copper has 70.3% silver)

Function of Amalgam Constituents

• Silver (Ag):
  • Crucial in the reaction and provides its alloy color -Reduces creep -Increases strength, setting expansion & resistance to tarnish
• Tin (Sn):
  • Controls the reaction between silver and mercury, preventing unacceptable speed and expansion -Reduces strength, hardness, resistance to tarnish and corrosion
• Copper (Cu): -Increases hardness & strength -Increases setting expansion
• Zinc (Zn): -Acts as a scavenger during manufacture -Reduces brittleness in the amalgam form -Can cause delayed expansion with moisture contamination

Classification of Amalgam Alloys

• Based on copper content (low copper, high copper) and zinc content (zinc containing, zinc-free).
• Based on the shape of the particles (lathe-cut, spherical, mixed shapes)
• Further classified as binary (e.g., silver-tin), ternary (e.g., silver-tin-copper), or quaternary (e.g., silver-tin-copper-indium) alloys based on the number of metals

Properties of Set Amalgam

• Dimensional changes are minimal after setting, with slight expansion or contraction
• Initial contraction period (first 20 minutes) occurs due to mercury dissolving in alloy particles
• Expansion occurs later, possibly from mercury reacting with silver and tin
• Factors favoring contraction include: low mercury-alloy ratio, higher condensation pressure, smaller particles and longer triturating times
• Stable dimensions usually achieve after 6–8 hours
• Delayed expansion can occur due to zinc contamination with water during trituration or condensation, spanning 3–5 days to months

Strength of Amalgam

• Good compressive strength but does not withstand high tensile/bending strength
• Cavity design crucial for minimizing tension/shear forces during service
• Factors affecting strength include: triturating (under-trituration/over-trituration), mercury content, and condensation pressure
• Initial strength gain takes time. At least 70% of its strength is gained within 8 hours post placement
• Cavity design to reduce tensile stresses, with sufficient depth in the amalgam
• Porosity weakens the material

Creep as a Factor in Amalgam

• Creep is a time-dependent permanent deformation under static or intermittent loads
• Low-copper amalgams exhibit higher creep rates linked to marginal deterioration
• High-copper amalgams exhibit lower creep rates