Dental Amalgam Chapter 5 Quiz

Introduction to Dental Amalgam

• Dental amalgam has been a standard restorative material for over 150 years, primarily for posterior restorations.
• Its popularity is due to its ease of manipulation, cost-effectiveness, and longevity.
• Although there are concerns regarding mercury toxicity, dental amalgam is generally considered to present an acceptable risk-to-benefit ratio when used properly.

Composition of Dental Amalgam

• Dental amalgam consists of mercury combined with an alloy of silver, tin, copper, and sometimes zinc or other trace metals.
• An amalgamation reaction occurs when the alloy is mixed with mercury, resulting in a hard, silvery-gray restorative material.

Alloy Composition and Properties

• Common composition for conventional amalgam alloy includes:
  • Silver (Ag): 40-60%
  • Tin (Sn): 27-30%
  • Copper (Cu): 13-30%
  • Zinc (Zn): up to 2%
  • Mercury (Hg): 3%
• Each metal serves distinct roles:
  • Silver enhances strength and expansion, minimizes creep.
  • Tin increases reactivity and corrosion but decreases strength.
  • Copper improves strength and corrosion resistance.
  • Zinc adds plasticity and prevents oxidation.

Classification of Amalgam

• Amalgam can be classified based on several criteria:
  • Number of alloyed metals
  • Shape of the particles
  • Copper content: low (<6%) vs. high (>6%)
  • Zinc content: zinc-containing (>0.01%) vs. zinc-free (<0.01%)
  • Unmixed vs. admixed types

Advantages and Disadvantages

• Advantages:
  • High compressive strength and durability.
  • Ease of handling and manipulation.
  • Excellent wear resistance and distinction from tooth structure.
  • Cost-effective restoration option.
• Disadvantages:
  • Aesthetic concerns due to silver color.
  • Potential mercury exposure and related health hazards.
  • Possible occurrence of amalgam tattoos and lack of insulation.

Properties Affecting Amalgam Restorations

• Dimensional Changes: Proper dimensioning is critical; large contractions can lead to gaps, while expansions may cause sensitivity.
• Strength: Amalgam gains strength over time. It reaches 90% strength within 24 hours and is weaker shortly after placement.
• Creep: Amalgam may undergo plastic deformation under stress.
• Corrosion & Tarnish: Corrosion affects mechanical properties and is accelerated in contact with other metals; tarnish primarily affects the surface.
• Thermal Properties: Amalgam has a higher thermal conductivity than dentine, leading to potential issues with microleakage.
• Biological Properties: Mercury compounds may impact the nervous system, and allergic reactions might occur.

Manipulation of Amalgam

• Key steps for amalgam manipulation include:
  • Proportioning & Dispensing: Ratio of alloy to mercury typically ranges from 5:8 to 10:8. Optimal final mercury content is under 50%.
  • Trituration: Mixing can be done mechanically or manually, with mechanical being more common for consistency and efficiency.
  • Condensation: Proper condensation ensures ideal adaptation within the cavity and reduces porosity.
  • Carving: Carving after condensation must be timely to avoid hardening.
  • Polishing: Polishing is performed after achieving adequate strength to enhance aesthetics and resistance to corrosion; usually requires a 24-hour delay post-placement.

Conclusion

• The dental professional is responsible for the correct use and preparation of amalgam to ensure quality restorations.
• Proper handling and preparation are critical to avoiding faulty restorations that may jeopardize tooth integrity.