Table 1.

Thornhill grading: grading of strength of association between mucosal lesions and amalgam/metal

Type I	No association	No lesions in direct contact with amalgam restorations. Lesions have typical bilaterally symmetrical distribution of oral lichen planus or are restricted to areas of the palate, gingivae, or outer surface of the lip that do not come into contact with the teeth
Type II	Weak association	Some amalgam restorations in contact with affected areas of mucosa. However, < 25% of affected mucosa in direct contact with amalgam restorations. Some amalgam restorations may also be in direct contact with unaffected areas of oral mucosa
Type III	Strong association	> 75% of affected mucosa in direct contact with amalgam restorations. No amalgam restorations in direct contact with unaffected areas of oral mucosa
Type IV	Very strong association	Lesions restricted to but affecting all areas of mucosa in direct contact with amalgam restorations