Dental Amalgam

• What is an amalgam?

  An alloy, one of the constituents of which is mercury. A mixture of two or more metals, one of which is mercury
• What is Dental Amalgam?

  Mercury + Silver/tin alloy (amalgam alloy) Amalgamation reaction results in hard shiny silver grey restorative
• What are the components of Dental Amalgam?

  • Silver 40 -70%
  • Tin 12-29%
  • Copper 12-30%
  • Zinc 0-1%
  • Mercury 40-50%
• What is the Intermetallic phase referred to as the gamma (γ) phase which readily amalgamates with Hg

  Silver/Tin/Copper Alloy
• What is the role of Tin in Dental Amalgam?

  < 25% expansion Pain > 29% contraction Marginal Gap
• What is the role of Copper in Dental Amalgam?

  Increases strength

  Reduces tarnish, corrosion, creep, marginal deterioration
• What is the role of Zinc in Dental Amalgam?

  • Scavenges O2
  • keeps alloy clean during production
  • Lowers rate of marginal fracture (delays corrosion)
  • Moisture contaminated Zinc containing alloys may cause: Delayed expansion, Surface blistering, Internal corrosion
• Is the copper content in modern amalgams higher or lower?

  Higher
• Sn (Tin) has greater affinity for Cu (Copper) than Hg (Mercury) - True or False?

  True
• What does Copper combine with to for the 'eta' phase?

  Cu (Copper) combines with Sn (Tin) to form 'eta' phase
• What do you begin with in the setting reaction?

  A Ternary alloy (Ag-Sn-Cu) + Mercury (Hg)
• Gamma product of setting reaction

  Ag-Sn-Cu Silver/Tin/Copper
• Gamma 1 product of setting reaction

  Ag2Hg3 Silver/Mercury
• Eta phase

  Copper/Tin Cu6Sn5
• Does Hg (Mercury) diffuse into the outer or inner layer of Ag-Sn-Cu particles?

  Outer layer
• Name 7 key material characteristics for amalgam

  Ease of manipulation Acceptable marginal adaptation Technique insensitivity Self-sealing ? Biocompatibility ? Mechanical properties/Wear resistance Low cost
• Ideal range of mercury content?

  Ideal range is 44-48 wt.%
• What happens if the mercury content is >55wt.%

  ↓ strength, ↑ corrosion, ↑ creep
• Where is amalgam weakest?

  Brittle at thinnest parts
• After how much time does amalgam set?

  24h+ to reach 100% By 1h, 40-60%
• A mechanical property of amalgam?

  Strength
• Why is mercury used in amalgam?

  Flexibility, Liquid at room temperature, Mixed with alloy powder, its soft enough to mold into tooth, Durability
• What are the consequences of 'Creep', a physical property of amalgam

  - Amalgam flows over marginal ridge - Thin sections fracture easily - Marginal deterioration; 'ditching
• When does creep increase?

  - Creep ↑ as melting point is reached - Phases containing ↑ Hg result in ↑creep
• Key factors in Microleakage

  - 2-20µm gap - Poor condensation technique - Corrosion by-products - Differences in TEC
• What does Trituration mean?

  The mixing of amalgam alloy particles with mercury in a device called a triturator.
• What happens when amalgam is polished?

  Heat is generated Aerosol generating procedure (AGP)
• 4 Operator Variables

  Proportioning • Trituration • Condensing • Carving / Polishing
• Why is the use of amalgam reducing?

  Concern with the use of mercury Aesthetic reasons - people want tooth coloured material Better and newer materials have been invented Minimally invasive dentistry
• Where can amalgam end up which causes concerns environmentally?

  • Major amalgam particles (∼15%) - Surplus in trituration capsules - Carved surplus • Minor amalgam particles (<10%) - Produced during carving, polishing (sucked up and transported via vacuum) • Lost or extracted teeth (solid watse)
• Why should a finished amalgam restoration have a well contoured smooth surface flush with the cavity margins?

  1) Prevention of food retention 2) prevention of plaque retentive factors 3) Prevention of corrosion 4) Corrosion of small defects in contour 5) Patient motivation
• What is the Beilby layer?

  - A layer which is amorphous and resistant to corrosion - A microscopic deformed layer at the surface of a material that produces a reflective surface
• Sufficient strength and hardness are achieved in amalgam restorations after how long?

  24 hours
• Careless brushing/polishing of amalgams can lead to?

  - severe soft tissue damage- abrasion of tooth/restoration- over-heating
• What are the advantages of high-copper amalgams?

  • high strength
  • less corrosion and tarnish
  • less creep
  • minimal sensitivity to handling variables
  • producing long-term clinical results
  • fewer incidences of marginal failure
• What is the typical composition of amalgam?

  
• What does zinc do in amalgams?

  Brings down the oxidation of other alloys in the metal, meaning longer life
• What is 'Creep'?

  - Creep is a gradual change in shape due to compression because of dynamic intra-oral stresses- Causes the flow of amalgam
• What strength properties does amalgam have?

  • High compressive strength
  • Poor tensile and shear strength
  • Brittle when places in thin sections due to low edge strength
  • Require adequate bulk for strength
  • Increased mercury, decreases stength

  
• Describe composition of Conventional Dental Amalgam: (Low copper)

  • Ag 65-70%
  • Sn 30%
  • Cu less than 6%
  • Zn less than 1% if any
  • Ag-Sn forms a solid intermetallic compound Ag3Sn when mixed with liquid mercury in gamma phase