Dentistry

Amalgam Fillings

Lecture note on Amalgam Fillings

General information

Amalgam Fillings Or Dental Amalgam has been the most widely used material for the restoration of posterior teeth due to:

  1. High strength and durability
  2. Ease of use
  3. Good physical characteristics

However, its use has decreased over the past decade due to concerns regarding:

  1. Esthetics
  2. Mercury content

Alloy versus amalgam

Alloy: is a mixture of two or more metals.
Main components of amalgam alloy:

  1. Silver
  2. Tin
  3. Copper
  4. Zinc
  5. Palladium or indium

When these components are mixed with mercury, the reaction that occurs is amalgamation and the resulting material is dental amalgam.

Composition

Weight (%)
Metals
Limits prior to 1986    (conventional alloy)   
Current limits
(Cu-rich alloy)
Silver
65 (min)
40 (min)
Tin
29 (max)
32 (max)
Copper
6 (max)
30 (max)
Zinc
2 (max)
2 (max)
Mercury
3 (max)
3 (max)

Classification

According to the shape of particles in the powder:

  1. Irregular: Formed by shaving particles from a block of the alloy by a lathe (lathe-cut alloy)
  2. Spherical: Formed by spraying molten alloy into an inert gas (spherical alloy)
  3. Admixed: Mixture of the two (admixed alloy). Alloy maybe made from different particle shapes to increase packing efficiency and reduce amount of Hg needed to obtain a workable mix.
Amalgam Fillings

According to composition:

  1. Conventional alloys (6% copper content, refer to Table 1)
  2. Copper enriched alloy:

Single composition-copper enriched alloys
Dispersion modified-copper enriched alloys: ratio is 2 (conventional alloy): 1 (silver-copper alloy), overall copper content 12%

Setting transformation

  1. Alloy powder + liquid mercury mixed  Packable amalgam in a cavity firming phase of the mix  1st stage of firming amalgam can b carved.
  2. When amalgam reaches initial set, it cannot be carved, but still not fully reacted (brittle). Needs 24 hours to attain full strength.
Amalgam Fillings

When the alloy is mixed with mercury, three phases occur:

  1. Gamma phase (γ) silver-tin alloy phase, strongest with least corrosion
  2. Gamma 1 phase (γ1) consists of mercury reacting with silver, not as strong as γ.
  3. Gamma 2 phase (γ2) consists of mercury reacting with Tin. Weak phase and corrodes easily.