Lichenoid reactions of murine mucosa associated with amalgam.

Background: In 97% of all patients with oral lichenoid reactions (OLR) associated with dental amalgam a removal of the fillings leads to a decline of the lesions, as a minimum.

Objectives: The aim of this study was to determine if contact allergic or local toxic effects or both may contribute to OLR using an animal model with mercury-sensitive and non-sensitive rats.

Methods: Twenty Brown Norway rats, which have a genetic predisposition for an autoimmune syndrome after exposure to mercury and 20 Lewis rats, not mercury sensitive, were treated as follows: 10 animals of each group were sensitized with a low dose of mercuric chloride. Half of all animals received local exposure of the right buccal mucosa to amalgam (left: control), the others to amalgam alloy free of mercury. All rats were patch tested with an amalgam series.

Results: After 20 days of exposure 96% of all animals showed white mucosal lesions restricted to the contact zone of the alloy on the treated side, but only up to 25% had a positive patch test reaction to amalgam or inorganic mercury (INM). The lesions showed no relation to species, alloy, sensitization or patch test reaction.

Conclusions: While allergic mechanisms may contribute to mucosal contact lesions in Brown Norway rats, this is less probable in Lewis rats. Mercury in general appears to be irrelevant in the development of ORL in this study. If this holds true for humans as well, patch testing with an amalgam series may be helpful in a minor fraction of all patients with OLR.