Dental Amalgam Strength and Bonding Quiz

Properties of Dental Amalgam

• Must be at least 80% of the final strength according to ANSI/ADA specifications
• Viscoelastic in nature, making strength and modulus of elasticity sensitive to rate of loading
• Higher rate of loading increases compressive strength and modulus of elasticity

Bond to Tooth Structure

• No true adhesive bond between amalgam and tooth structure, only mechanical retention
• Requires insulating base to prevent thermal irritation to the pulp in deep cavities

Biological Properties

• Thermal irritation: amalgam is a metallic restoration that requires an insulating base to prevent thermal irritation to the pulp
• Corrosion: dental amalgam always corrodes, which can lead to increased porosity, marginal breakdown, loss of strength, and release of metallic products into the oral environment
• Methods to reduce corrosion:
  • Use of low mercury alloy ratio to reduce reaction products
  • Use of high copper amalgam alloys to be free of γ2 phase
  • Finishing and polishing of amalgam restoration to produce a smooth surface
  • Use of low mercury/alloy ratio to reduce the risk of exposure of mercury vapor

Condensation

• Objective is to yield a restoration with optimal adaptation to the cavity walls, reduce mercury content, and reduce porosity
• Delayed condensation permits the amalgam to set partially before being transferred to the prepared cavity
• Effects of delayed condensation:
  • Reduction in strength due to breaking up of the already formed matrix
  • Increase in mercury content
  • Reduction in plasticity, which decreases adaptation to the prepared cavity

Carving, Finishing, and Polishing

• Carving: reproduces the proper tooth anatomy
• Polishing: achieves a lustrous surface with better corrosion resistance
• Conventional low-copper amalgams are polished not less than 24 hours after insertion

Dimensional Changes

• Dimensional changes between 5 minutes and 24 hours after amalgam insertion must be ±20µm/cm according to ANSI/ADA specification
• Initial contraction in the first 20 minutes due to diffusion of mercury between the alloy particles and solution of the alloy particle's surfaces into mercury
• Expansion occurs due to reaction of mercury with the alloy particles and formation of new phases
• Dimensions become nearly constant after 6-8 hours
• Net total dimensional change remains negative (contraction) due to the use of spherical dental amalgam alloy, low mercury/alloy, and mechanical amalgamators during trituration

Test your knowledge on the strength, modulus of elasticity, and bonding characteristics of dental amalgam according to ANSI/ADA specifications. Understand the importance of testing properties at the same rate of loading and the lack of true adhesive bond with tooth structure.