Dental Problems

Dental Amalgam Fillings – Review

DenturesDental amalgam fillings are one of the tooth restorative materials. But, they are considered not to be safe as they contain mercury which is harmful element. In this article, there is a brief discussion on the dental amalgam fillings. Read on to know more.

Constituents:

  • Amalgams that contain zinc appear to exhibit a lower rate of marginal failure under clinical loading but they tend to exhibit excessive delayed expansion if contaminated with moisture during placement.
  • A number of elements such as indium, platinum and palladium may be included in the alloy in minor quantities.

Packability of dental amalgam fillings:

  • Packability refers to the resistance offered by the amalgam to the forces of condensation used in placing the amalgam.
  • It varies according to the size and proportional distribution of lathe-cut or spherical particles.
  • Amalgams containing only spherical particles are relatively easy to pack.

Trituration of dental amalgam fillings:

  • The object of trituration is to completely wet the entire surface of all the alloy particles with the mercury, to bring about the process known as amalgamation.
  • Amalgamators are made to work at different speeds and the action must be checked periodically.
  • The efficiency can be tested with a trial mix.
  • The freshly mixed mass is dropped on to the bench from a height of approximately 30cm.
  • If the mix is dry and crumbled, the trituration time must be increased.
  • A well mixed amalgam must stay together when dropped on the bench but must be a little flattened and retain a wet gloss on the surface.
  • It is better to slightly over triturate than to under triturate an amalgam because greatly extended trituration may reduce plasticity, shorten working time and increase final contraction.

Condensation:

  • Condensation refers to the incremental placement of the amalgam into the prepared cavity and compression of each increments to form a continuous homogenous mass that is well adapted to all the margins, walls and line angles.
  • It is best carried, out using hand instruments with a smooth flat face that can deliver reasonable force per unit area to the amalagam and compress the layers together.
  • Mechanical condensers are available and they reduce the need for the application of load.
  • However, there is an undesirable generation of heat and mercury vapour.
  • Ultrasonic condensation has been suggested but it is not recommended because it allows the release of considerable quantities of mercury vapour into the ambient atmosphere with a consequent risk to the operators.

Placement and finishing of dental amalgam fillings:

  • Following trituration the amalgam should be condensed into the cavity within four minutes.
  • It can then be burnished towards the margins and carved to an approximate occlusal form.
  • At a subsequent appointment any necessary final adjustment can be carried out to the occlusal and proximal surfaces.

Structure of the set amalgam:

  • Provided the minimal amount of mercury, commensurate with complete amalgamation, is incorporated initially, and then proper condensation techniques are carried out, approximately 35 -50% of the final volume of the set amalgam will consist of unreacted portions of alloy particles, held together by the γ phase matrix.

Moisture contamination:

  • It is essential to keep the amalgam completely free from moisture contamination during the entire placement procedures following trituration.
  • The cavity must be completely dry and free of gingival seepage or haemorrhage.
  • Inclusion of water will lead to increase in corrosion and tarnish with a reduction of physical properties.
  • A zinc containing amalgam will develop a delayed expansion.

Marginal sealing and bonding:

  • This means that a newly placed amalgam will be subject to a degree of microleakage and it is desirable to take steps to overcome this. There are two alternatives available for this.
    • Copal varnish:

      This has been used for many years and provides an immediate deal that will last for a limited time only. It is recommended that it be placed in two applications of a very thin coat and the vehicle be allowed to evaporate briefly.

    • Resin bond: There has been a move lately to replace the copal varnish with an unfilled resin bond such as an enamel bonding agent with composite resin. The theory behind this is that the resin bond will develop some degree of union with enamel and dentin on one side and amalgam on the other side and thereby both seal the margin as well as strengthen the tooth crown and compensate to some degree for the destruction caused by cavity preparation.A bond with a very low viscosity should be used and placed carefully in a single layer, taking care not to allow it to puddle in the corners. It should then be light activated before placing the amalgam so that it will not be incorporated in the amalgam during condensation.

Limitations:

  • The biocompatibility of amalgam has been the subject of extensive investigation, particulary in relation to the presence of mercury. Mercury in dental amalgam may pose threats to the health of patients to the health of dental care providers and to the environment.

Alternative to amalgam:

  • In view of the mercury presented in amalgam, a mercury free alloy has been suggested, and which is none other gallium.
  • Certain drawbacks of dental amalgam, noticeably that of potential mercury poisoning have lead to the development of newer materials.
  • One such material is gallium alloy, a mercury free metallic substitute to silver amalgam.
  • A study was conducted in our department using gallium alloy as a restorative material in pediatric patients and it has shown encouraging results.

The above article discusses briefly about the dental amalgam fillings -constituents, packability, trituration, condensation, placement and finishing. It also discusses about the structure of the set amalgam, moisture contamination, marginal sealing and bonding, limitations and alternative to amalgam. One should make sure to know the pros and cons of the dental filling before going for the filling.

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