Metallothionein in human gingival amalgam tattoos

Amalgam tattoos occur when small particles of dental amalgam, composed larg ely of silver (Ag) and mercury (Hg), are inadvertently implanted into oral soft tissues during dental procedures. Metallothioneins (MTs) are ubiquitou s, low molecular weight, cysteine-rich, metal-binding proteins that are ind ucible by many agents including metals and may be involved in the detoxific ation of toxic metals such as Hg. In this study, the correlation between MT expression and amalgam tattoos in human gingiva was investigated using ene rgy-dispersive X-ray microanalysis (EDX) and immunohistochemical techniques . Light microscopically, amalgam tattoos presented as either fine granular particles or larger discrete opaque globular particles in connective tissue s. EDX revealed the smaller particles to be silver sulphide (Ag2S), while t he larger particles exhibited a shell of Ag2S that contained irregularly di stributed masses of Ag and Hg. Particles of tin (Sn) were also found. No MT staining was observed in collagen, fibroblasts or blood vessels in areas e xhibiting abundant amounts of embedded fine granular Ag2S particles. Blood vessels exhibiting relatively few amalgam particles stained positively for MT. Cells with the morphological features of histiocytes located directly a djacent to larger pieces of amalgam showed intense MT staining. These resul ts indicate that amalgam tattoos contain no Hg or free Ag except in large g lobular pieces of amalgam, which still contain Hg and which induce MT expre ssion in adjacent histiocytes. This suggests that Hg leaching from impacted dental amalgam particles induces MT, while residual Ag2S and Sn particles do not. MT may therefore act to reduce Hg exposure in patients with amalgam tattoos. (C) 2001 Elsevier Science Ltd. All rights reserved.