Oral lichenoid lesions caused by allergy to mercury in amalgam fillings

Oral lichenoid lesions (OLL) or lichen-planus-like lesions are often idiopathic. Our aim was to determine whether OLL can be caused by allergy to mercury in amalgam fillings, and whether resolution of OLL occurs after replacement of amalgam with other dental filings. Patients with only OLL (except for 1 case with cutaneous lichen planus) referred for patch testing during 1985-1994 to the Contact and Occupational Dermatitis Clinic of the Skin & Cancer Foundation, Darlinghurst, were reviewed. Patch tests were performed with 1% mercury, 1% ammoniated mercury, 0.1% thimerosal, 0.1% mercuric chloride, 0.05% phenylmercuric nitrate and an amalgam disc, using Finn Chambers occluded for 2 days. 19 patients (17 women and 2 men; age range: 28-72 years) had OLL in close contact with amalgam fillings and showed positive patch test reactions to mercury compounds. 16 out of 19 patients had their amalgam fillings replaced. In 13 patients, the OLL healed. 1 patient had marked improvement. 1 patient had no improvement and developed multiple oral squamous cell carcinoma. In conclusion, OLL can be caused by allergy to mercury in amalgam fillings. Replacement of amalgam with other dental fillings usually results in resolution of OLL and is recommended for cases with positive patch test reactions to mercury compounds.