Oral lichen planus and contact allergy to mercury.

29 patients with oral lichen planus and amalgam fillings were patch tested for contact allergy to dental materials. 18 of these patients (62%) had a contact allergy to mercury. In a control material, the frequency of mercury allergy was 3.2%. In 3 of the patients the lesions healed completely after removal of the amalgam fillings. On the basis of these findings it is recommended that all amalgam fillings be removed after a positive patch test to mercury, as a step in the treatment of oral lichen planus.