What is a lichenoid amalgam reaction?
Lichenoid amalgam reaction, also known as amalgam associated oral lichenoid reaction, is an uncommon allergic reaction following long exposure to dental amalgam filling(s).
Who gets a lichenoid amalgam reaction?
Like oral lichen planus, it affects women more commonly than men, and is most common in middle age. It occurs adjacent to an amalgam dental filling.
Clinically and histologically, it is indistinguishable from idiopathic oral lichen planus.
The clinical clues that it may suggest this diagnosis are:
- close proximity to a dental amalgam filling
- localised lesion
The buccal mucosa (inside of the cheek) is the most common site affected, with the border of the tongue the next commonest.
Oral lichenoid lesions have been classified into three groups based on the relationship to the amalgam filling:
- Group I – lesion is limited to the area in direct contact with the amalgam filling
- Group II – the lesion exceeds the area of contact
- Group III – the lesion shows no contact with an amalgam filling.
As with idiopathic oral lichen planus, there are four clinical patterns – reticular, erosive, atrophic and plaque-like, with the reticular pattern seen most commonly.
The lesion may be asymptomatic or show symptoms such as pain or sensitivity to eating hot or spicy foods.
How the diagnosis is made
The diagnosis will be suspected clinically because of the close relationship between the lesion and a dental amalgam filling. However idiopathic lichen planus can develop at sites of trauma such as rubbing from rough dental restorations. Signs of lichen planus elsewhere including in the mouth, skin, nails and scalp should be looked for.
A biopsy of the lesion will show the same histological features as idiopathic oral lichen planus. Immunofluorescence may be done to exclude autoimmune diseases of the mouth, and again is the same as for idiopathic oral lichen planus.
Patch testing with amalgam and inorganic mercury salts will be positive more commonly in patients with lichenoid amalgam reaction than in those with idiopathic oral lichen planus. However a negative result does not exclude the diagnosis. Therefore the role of this test in making the diagnosis is unclear.
The only diagnostic test is the response to replacement of the amalgam filling with an alternative filling material. The effect of removing the amalgam however cannot be predicted by the biopsy histology or patch test results.
If the lesion is symptomatic, replacement of the amalgam with an alternative filling material is recommended. In European studies, over 90% of patients showed a marked improvement or disappearance of the lesion following replacement of the filling, especially for Group I lesions and those on the tongue. Complete clearance was most likely to occur in Group I patients with a positive patch test reaction to amalgam.
However, if the lesion is not causing symptoms or the patient has lichen planus of the skin, annual review and use of alternative fillers for future dental work is suggested.
In addition, the following treatments may be helpful:
- potent topical steroids such as clobetasol propionate
- other topical treatments such as tacrolimus
- oral medications including oral steroids such as predniso(lo)ne.
No progression to oral cancer has been reported to date from an oral lichenoid lesion adjacent to amalgam.
Lichenoid amalgam reaction appears to be a cell-mediated delayed (type IV) contact hypersensitivity to either the mercury or another component of the amalgam.