In this article of Amalgam Failure, we discuss another type of failure which is Severe or excessive discolouration. We will explain the major causes, clinical picture and treatment.
Excessive Discolouration
Causes
- Tarnish.
- Corrosion.
- Amalgam Blues.
Cause 1: Tarnish
- Formation of a surface film of discolouring oxides and sulphides leading to loss of amalgam luster.
- This is enhanced by: Excess Hg, under trituration, improper condensation, Lack of finishing, moisture contamination, and bad oral hygiene.
Cause 2: Corrosion
- Its the actual disintegration of the bulk of amalgam.
- Chemical corrosion: due to Lack of polishing and food stagnation which may lead to halogenation and sulfurization.
- Electric corrosion: Setting of electromotive force between two different electrodes of different electric potential through an electrolyte.This occurs between two dissimilar metallic restorations, as:
- Old and new similar metallic restoration.
- Polished and unpolished areas of the same restoration.
- The same restoration but heterogeneous in structure.
- Concentration cell corrosion
- It is a type of electric corrosion resulting from accumulation of certain types of food on a site of restoration making it different in its electric potential from other sites of amalgam. It is increased with rough surfaced amalgam and bad oral hygiene.
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Cause 3: Amalgam blues
This type of discolouration is by the amalgam being seen through the enamel, It is mainly due to:
- Thin or undermined enamel that shows dark blue discoloration of amalgam.
- Penetration of metallic ions and corrosive products of amalgam through the dentinal tubules.
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Clinical Picture
- Tarnish: Loss of surface luster.
- Corrosion: Rough pitted amalgam surface.
- Amalgam blues: Dark bluish discolouration.
Treatment
- Tarnish: requires re-polishing.
- Corrosion: may require removal of old restoration followed by bleaching and correct replacement.
- Amalgam blues: are prevented with application of cavity varnish to seal dentinal tubules from penetration of metallic ions.
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