Podcast
Questions and Answers
What is the dimensional change requirement between 5 minutes and 24 hours after amalgam insertion according to ANSI/ADA specification 8?
What is the dimensional change requirement between 5 minutes and 24 hours after amalgam insertion according to ANSI/ADA specification 8?
What is the reason for the initial contraction in the first 20 minutes after mixing the alloy powder with mercury?
What is the reason for the initial contraction in the first 20 minutes after mixing the alloy powder with mercury?
What causes the dimensions to become nearly constant after 6-8 hours following amalgam insertion?
What causes the dimensions to become nearly constant after 6-8 hours following amalgam insertion?
Which factor contributes to marginal adaptation and seal in dental amalgam restorations?
Which factor contributes to marginal adaptation and seal in dental amalgam restorations?
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What will occur with high mercury/alloy content in amalgam restorations?
What will occur with high mercury/alloy content in amalgam restorations?
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Study Notes
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
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Description
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.
