What are the factors affecting dimensional change of amalgam?
- Hg content
- Condensation pressure
- Water contamination
- Particle size
Effect of low Hg content on dimensional change of amalgam?
Low Hg content: Inadequate Hg for amalgamation, decreased expansion, less dimensional change
Effect of high condensation pressure on strength of amalgam?
High condensation pressure: (Lathe cut alloys) increased compressive strength
Effect of high condensation pressure on the dimensional change of amalgam?
High condensation pressure: Increased expansion, greater dimensional change
Effect of high Hg content (>55%) on strength of amalgam?
High Hg content: increased residual Hg, increased creep rate, decreased strength
Effect of particle size on dimensional change of amalgam?
The smaller the particle size, the greater the surface area for reaction to occur, the larger the initial contraction (greater dimensional change)
What are the factors influencing strength of amalgam?
- Hg content
- Trituration time
- Condensation pressure
- Porosity
Effect of water contamination on the dimensional change of amalgam?
Water contamination before/during condensation of amalgam causes corrosion of the zinc component in amalgam, leading to formation of H2. H2 collects within amalgam and exerts and outward pressure, leading to expansion of restoration, hence increased dimensional change
Effect of trituration time on strength of amalgam?
Increased trituration time (up to a limit) increases strength of amalgam; Over or under-trituration decreases strength of amalgam
What are the factors influencing creep rate of amalgam?
- Hg content
- Condensation pressure
- Trituration time
- Copper content
What is the clinical significance of marginal defects?
- Leakage
- Sensitivity
- Secondary caries
- Corrosion
- Clinical failure
What types of corrosion is amalgam susceptible to?
- Chemical corrosion: Direct chemicals from food interact with components of amalgam
- Electrochemical corrosion: When 2 dissimilar restorations are in contact (ie. Gold and amalgam)
What are the advantages of amalgam as restorative material?
- Easily distinguishable from tooth structure - In the event where restoration needs to be replaced, it is easy to remove the old/damaged amalgam restoration
- Less microleakage: Corrosion occurs at interface between amalgam and tooth (self-sealing)
- Minimal shrinkage as compared to CR
- Less technique sensitive as compared to CR/GIC
- Shorter time for placement than CR/GIC
- Good handling properties
- Proven clinical longevity
- Inexpensive
- Newer formulations havre greater resistance to surface corrosion
What are the disadvantages of amalgam as a restorative material?
- Not aesthetic - Non-tooth coloured
- Prone to LT corrosion and tarnishing
- Risk of galvanism
- Risk of mercury toxicity
- No adhesion to tooth structure: Retention in oral cavity is dependent on the retention form of cavity preparation
- Limited working time before set
- Marginal breakdown
What are some factors to reduce corrosion of amalgam?
- Proper finishing of surface of restoration
- Proper trituration and condensation techniques
- Avoid placing dissimilar restorations in contact with each other
- Reduce final Hg content
- Use a fine particle alloy
- Use non-gamma 2 alloys (to remove the weakest phase/most susceptible phase to corrosion)
What are factors contributing to corrosion of amalgam?
- Surface voids and irregularities
- Presence of 2 dissimilar restorations in contact
- Indirect effect of excess Hg
- Diet of patient can contribute to chemical corrosion
