Monday, October 24, 2011

A NOTE ON DENTAL AMALGAM


DENTAL AMALGAM
General information
Dental amalgam has been the most widely used material for the restoration of posterior teeth due to:
High strength and durability
Ease of use
Good physical characteristics
However, its use has decreased over the past decade due to concerns regarding:
Esthetics
Mercury content
Alloy versus amalgam
Alloy: is a mixture of two or more metals.
Main components of amalgam alloy:
Silver
Tin
Copper
Zinc
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:


  • Irregular: Formed by shaving particles from a block of the alloy by a lathe (lathe-cut alloy)
  • Spherical: Formed by spraying molten alloy into an inert gas (spherical alloy)
  • 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.

According to composition:
Conventional alloys (6% copper content, refer to Table 1)
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
  • Alloy powder + liquid mercury mixed  Packable amalgam in a cavity firming phase of the mix  1st stage of firming amalgam can b carved.
  • When amalgam reaches initial set, it cannot be carved, but still not fully reacted (brittle). Needs 24 hours to attain full strength.

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

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

7 comments:

  1. A dentist can help you prevent tooth decay, which can lead to tooth loss. Although many people are reluctant to visit a dental care provider, it is vital to go to make sure that you do not have gum disease. The dental care provider may suggest that you have a deep cleaning and continue good hygiene practices at home. Sometimes the dental care provider may suggest that you use a specially formulated product to improve the condition of your gums. A large number of American people will eventually suffer from gum disease and some will lose their teeth due to improper dental care. It is recommended that you go to the dentist at least twice a year to get your teeth cleaned. You also need to be sure to brush your teeth at least twice a day and use floss to clean areas between your teeth.

    Dentist Lancaster

    ReplyDelete
  2. How can one download the slides?

    ReplyDelete
  3. How can one download the slides?

    ReplyDelete
  4. click here

    intereting to see all the different types of chemical reactions

    ReplyDelete
  5. Thanks for posting this valuable information, Its really helpful to keep our teeth healthy. Thanks for the post.
    Dentist in Sw11

    ReplyDelete

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