Dental Amalgam – Classification, Indications, Contraindications, Advantages and Disadvantages

Dental Amalgam is a restorative material which is made by combining Silver with mercury and other alloys to achieve the Ideal characteristics of a Dental Restoration. Dental Amalgam was first introduced in the 1820s and since then has been used by Dentists across the Globe thanks to its High Compressive Strength, High wear resistance and mainly its long term clinical results. The other major factor when compared to other recent restorative material such as Composite, GIC, etc is the cost factor which lets Dentists use it more in Developing and Under-developed nations.

Dr. GV Black can be credited for standardizing Amalgam Restorations by giving a proper Composition for Amalgam and also showing Cavity preparation designs as Amalgam needs Mechanical Retention. The Alloy to mercury ratio and also the use of other alloys such as copper was decided in the 1960s to make Amalgam a better Restorative material.

Classification Of Dental Amalgam:

Classification of Dental Amalgam is done based on its Alloys, depending on the type of alloy, shape, size and how it is mixed, etc.

Based on Copper Content:

  • Low Copper Alloy – < 6% copper (conventional alloy)
  • High Copper Alloy – 6-30% copper content. It is divided into two types – Admixed and single composition alloy

Based on Zinc Content:

  • Zinc containing alloy – >0.01% zinc
  • Zinc free alloy – <0.01 zinc

Based on Shape of Alloy:

  • Lathe cut alloy: The particle size are irregular which is manufactures by milling an annealed ingot of alloy. This requires more mercury leading to inferior properties. It can resist more condensation pressure.
  • Spherical alloy: Particles are spherical and are manufactures by atomization of molten alloy. Less mercury is required which gives it better properties. It is more plastic and can take less condensation pressure in comparison to Lathe cut alloy.
  • Admixed alloy

Classification of Dental Amalgam

Based on Size of alloy particles:

  • Microcut
  • Fine-cut
  • Coarse-cut

Based on Number of Alloy metals:

  • Binary alloy (silver-tin)
  • Ternary alloy (silver-tin-copper)
  • Quaternary alloy (Silver-tin-indium)

Based on presence of noble metals:

  • Noble metal alloys (palladium, platinum, gold)
  • non-noble metal alloys

Based on Generations:

  • Basic silver-tin alloy
  • Low copper alloys (silver, copper < 4%, tin and zinc)
  • High copper alloys (single composition)
  • High copper alloys (admixed alloys)
  • Noble metal alloys
  • Gallium based alloys

Composition of Dental Amalgam:

Low Copper Alloys:

  • Silver: 63-70%
  • Tin: 26-28%
  • Copper: 2-5%
  • Zinc: 0-2%

Settings reaction of Low Copper Amalgam: Ag3Sn + Hg = Ag2Hg3 + Sn8Hg + Ag3Sn (Unreacted)

High Copper Alloys:

  • Silver: 69%
  • Tin: 17%
  • Copper: 13%
  • Zinc: 1%

Settings reaction of High Copper Amalgam: Ag3Sn + Ag-Cu + Hg = Ag2Hg + Sn8Hg + Ag3Sn (Unreacted)

Functions of Each component of Amalgam:

Silver (Ag): Increases Strength, Decreases setting time, tarnishes easily, whitens the alloy, decreases creep, Increases resistance to tarnish, increases the expansion on setting.

Tin (Sn): Improves physical properties when compounded with Silver, reduces setting expansion, reduces tarnish and corrosion, reduces strength and hardness

Copper (Cu): Increases hardness and strength, Increases setting expansion, reduces corrosion, decreases creep

Zinc (Zn): Reduces oxidation of other metals, delayed expansion with moisture contamination, acts as a scvanger

Indications of Dental Amalgam:

  1. Can be used as a permanent restoration material in Class I, Class II, Class V, Class VI caries
  2. Used in Pin retained restorations
  3. Post-endodontic access filling and core
  4. Cuspal restoration
  5. Die preparation
  6. Retrograde root canal filling material
  7. Interim restoration for teeth with questionable prognosis
  8. Cheaper and Economical

Contraindications of Dental Amalgam:

  1. Non-Esthetic (non-tooth color)
  2. Due to Mechanical retention – Extensive tooth preparation is required leading to loss of sound tooth structure
  3. Cannot be done in small Class I and Class II cavities as it requires removal of tooth structure to achieve retention, GIC is preferred in such cases.

Advantages of Dental Amalgam:

  1. High Compressive Strength
  2. Good wear resistance
  3. Ease of Use
  4. Economical
  5. Long-term results are very good
  6. Self sealing ability
  7. Can be bonded to tooth structure using adhesive

Disadvantages of Dental Amalgam:

  1. Not Esthetically pleasing
  2. Loss of Sound tooth structure
  3. Non-Insulating (it can transmit heat and cold sensations to the pulp)
  4. Corrosion and Galvanism are seen
  5. Difficulty in Restoring tooth shape and form
  6. Does not provide support or reinforcement to weakened tooth structure

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