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Koch et al published a study in 1999 on oral lesions related to dental restorations (1). They note that allergy to mercury as a cause of oral lichenoid lesions (OLL) remains controversial; some authors reporting a high frequency of sensitization to mercury and beneficial effect from removal of amalgam fillings in such patients, whereas others state that this procedure affects favorably all OLL, whether patients are sensitized to inorganic mercury or not. They attempted to determine the frequency of sensitization to metal salts in 194 patients (19 patients with OLL partly adjacent to amalgam fillings, 42 oral lichen planus (OLP) without close contact to amalgam, 28 other oral diseases, 46 oral complaints, 59 control group). They note that patch testing was performed with the German standard series, a dental prosthesis series, and a metal salt series including gold, mercury, and palladium salts as well as other salts of metals used in dental restorations. Late readings (10 and 17 days after application of the patch tests) were performed in all patients. They report that of 19 patients with OLL adjacent to amalgam fillings, 15 (78.9%) were sensitized to inorganic mercury (INM), significantly more than those with OLL not adjacent to amalgam, other oral diseases or complaints, and the control group. Amalgam was removed in 18 patients with OLL and in 11 patients with OLP. After removal it was noted that the lesions of 13 of 15 of the INM-sensitized patients with OLL (86. 7%) and 2 with OLP healed or improved significantly, but this was not observed with the INM negative patients. Additionally they note that frequency of sensitization to gold sodium thiosulfate (GST) and palladium chloride 1% pet (PDC) was high in all groups. This was partly because readings were performed late. Lesions of 2 patients with allergic contact stomatitis caused by gold and 1 caused by palladium healed completely after removal of these restorations. Histologically, lichenoid changes were observed in 14 of 36 biopsy specimens of positive patch tests from INM (9/21), GST (2/10), and PDC (3/5) in all patient groups, mainly in persistent patch tests at D10 or D17. This was not observed in 12 biopsy specimens taken from persistent patch tests from other substances, including nickel sulfate.

Earlier, in 1996, 118 patients with oral lichenoid lesions (OLL) topographically related to dental fillings were patch tested (PT) to reveal contact allergy to restorative materials (2). 80 (67.8%) patients displayed positive PT reactions to metals of dental filling materials: 76 reactions were found to various mercury compounds, 4 to sodium aurothiosulphate, 3 to stannic chloride and 2 to silver nitrate. They note that positive patch test reactions appeared more commonly in patients with restricted contact lesions (85.1%, type-1 lesions) as compared to patients with lesions exceeding to the adjacent areas (38.6%, type-2 lesions). The replacement of dental fillings was carried out in 62/80 PT-positive and 15/38 PT-negative patients. 28 out of 62 (45.2%) PT-positive and 3/15 (20%) PT-negative patients were reported to have shown complete healing of OLL after a mean follow-up time of 16 months. Complete healing occurred in 29/54 (54.0%) type-1 and 2/23 (8.7%) type-2 lesions. Topographical relation between the lesion and the filling material (restricted versus exceeding the contact area) indicated association of OLL lesion and the filling material, which could be further confirmed by patch testing in the majority of patients. They suggest that the patch test series should include mercuric chloride (0.1%), mercury (0.5%) and mercury ammonium chloride (1.0%), each in pet.

Another study investigating associations between dental restoration and oral mucosal disease was reported in 1996 (3). The subjects were 24 patients out of 479 tested, who had oral mucosal symptoms and positive patch test reactions in a dental series during 1987-1994 at the Department of Dermatology, Helsinki University Hospital. The clinical diagnoses were oral lichen planus (LPO, 13 patients), leukoplakia (2), glossodynia, i.e., 'burning mouth syndrome' (4), stomatitis (3) and recurrent angioedema (2). Only 1 patient had symptoms in relation to dental care. The authors report that all but 2 patients had allergic reactions to mercury (Hg) (12 patients), gold sodium thiosulfate (Au) (13 patients) or both. They propose that a clinical connection between oral symptoms and contact allergy was seen in 10 patients. 9 patients (7 LPO, 2 leukoplakia) had Hg allergy. In these cases, the oral lesions disappeared after the amalgam fillings had been removed. 1 patient had recurrent stomatitis and perioral eczema after dental care and 2,2-bis(4-(2-hydroxy-3-methacryloxypropoxy)phenyl)propane (BIS-GMA) allergy. Her symptoms were caused by drilling of acrylic fillings. In addition, a connection between localized stomatitis and contact allergy was considered probable in 2 cases. 1 patient had stomatitis from contact with an orthodontic device and nickel allergy. The other had stomatitis from contact with a dental gold crown and gold allergy. No clinical connection was reported between gold allergy and the oral symptoms of other patients.

A British study from 1996 also studied prevalence of mercury hypersensitivity in patients with oral lichenoid reactions (OLR) and the effect of amalgam replacement in subjects with amalgams adjacent to OLR irrespective of their mercury sensitivity status (4). 197 patients with oral problems were examined: 109 with OLR, 22 with oral and generalized lichen planus, and 66 with other oral diagnoses, including aphthous ulcers and orofacial granulomatosis. 19% of patients with OLR reacted to mercury on patch testing, significantly more than in those with generalized lichen planus (0%) and in those with other oral diagnoses (3%). Additionally they note that 22 patients with OLR and adjacent amalgams had amalgam replacement and, in 16 of 17 mercury-positive subjects and three of four mercury-negative subjects, the OLR resolved after amalgam removal.

Similar results were found in earlier studies (5-7).

A Cochrane Review on Interventions for treating oral lichen planus does not mention removal of amalgam fillings as a possible intervention (8)

1. Koch P, Bahmer FA,Oral lesions and symptoms related to metals used in dental restorations: a clinical, allergological, and histologic study, J Am Acad Dermatol 1999 Sep;41(3 Pt 1):422-30
2. Laine J, Kalimo K, Happonen RP, Contact allergy to dental restorative materials in patients with oral lichenoid lesions, Contact Dermatitis 1997 Mar;36(3):141-6
3. Alanko K, Kanerva L, Jolanki R, Kannas L, Estlander T, Oral mucosal diseases investigated by patch testing with a dental screening series, Contact Dermatitis 1996 Apr;34(4):263-7.
4. Ibbotson SH, Speight EL, Macleod RI, Smart ER, Lawrence CM, The relevance and effect of amalgam replacement in subjects with oral lichenoid reactions, Br J Dermatol 1996 Mar;134(3):420-3
5. Breatel J et al, Effect of replacement of dental amalgam on oral licheoid reactions, J Dent 1996, 24(1-2):41.
6. Pang BK, Oral lichenoid lesions caused by allergy to mercury in amalgam fillings, Contact Dermatitis 1995; 33(6): 423-7.
7. Bolewaska J et al, Oral mucosal lesions related to silver amalgam restorations, Oral Surg Oral Med Oral Pathol 1990; 70 (1): 55-8.
8. Chan ES-Y et al, Interventions for treating oral lichen planus, The Cochrane Library, last substantive amendment December 1998.