Definition
Amalgam tattoo is the most common cause of oral “pigmentation” and the most common intraoral pigmented patch. It results from iatrogenic implantation of dental amalgam particles into the oral mucosa. The mucosa is not truly pigmented — the colour is due to metallic particles embedded within the lamina propria and/or submucosa.
Etiology and Pathophysiology
Contributory factors :
- Implantation of dental amalgam into the oral mucosa, usually iatrogenic during a dental procedure.
- Contamination of mucosal abrasions by amalgam dust during procedures.
- Broken amalgam pieces falling into extraction sites.
- Residual material from endodontic root fills.
- Metallic particles driven into tissue by high-speed air turbines.
- Amalgam is usually traumatically implanted close to the dental arch.
- Only a very small amount of implanted amalgam is needed to produce a tattoo.
- Lesions are initially sharply defined, then the amalgam disperses and lesions slowly enlarge with irregular outlines; components dissolve, reprecipitate on nearby collagen, and particles are also dispersed by migrating macrophages (lateral spread may continue for several months).
Prevalence
- Most common nonphysiologic source of oral mucosal coloration is exogenous, and amalgam tattoo is the most common cause of oral “pigmentation.”
- Fragments of amalgam frequently become embedded in the oral mucosa, forming the most common intraoral pigmented patches.
Histological Features
- Amalgam seen as brown or black granules, with fine particles deposited along collagen bundles and around small blood vessels (silver has an affinity for collagen — silver salts/silver leaching stain the adjacent collagen and reticulin fibres brown, particularly around nerves and vessels).
- Early after implantation there is a foreign body reaction with macrophages or giant cells (large fragments surrounded by foreign body giant cells); this fades with time.
- Any free mercury solubilises within a few weeks and is excreted, remaining in the tissues only complexed within amalgam.
- Histology of other exogenous tattoos (graphite, ornamental) is similar, depending on the implanted material.
Clinical Features
Location
- Any mucosal surface — gingiva, alveolar mucosa, buccal mucosa.
- Gingiva and alveolar mucosa are most commonly affected.
- Typically in close proximity to amalgam-restored teeth or areas where such teeth were previously present.
Appearance
- Macules or slightly raised lesions; usually small (typically 5 mm or more across).
- Colour: black, blue, or grey (blue-grey to black; dark grey or bluish).
- Borders: well-defined, irregular, or diffuse (initially sharply defined, becoming irregular as the lesion enlarges).
- The mucosa is not actually pigmented — colour is from metallic particles embedded in the lamina propria/submucosa.
Differential Diagnoses
- Melanocytic / melanotic lesions (oral melanotic macule, oral melanocytic nevus, blue nevus).
- Melanoma (must be excluded if implantation cannot be confirmed).
- Other exogenous tattoos — graphite tattoo (pencil tip, accidental trauma) and ornamental/intentional tattoos, which may appear clinically identical.
- Metal-induced discoloration (e.g., lead “Burton line,” mercury/bismuth lines, argyria) — also not true pigmentation.
Relevant Clinical Investigations
- Radiographs: large/dense tattoos and metallic fragments may appear as densely radiopaque spots, aiding diagnosis without biopsy.
- Biopsy: required if a melanocytic lesion or melanoma is suspected, if fragments are too small to be seen radiographically, or where there is no record of implantation. Biopsy is diagnostic, though clinical and radiographic diagnosis may be adequate.
Patient Management
- No treatment required; the lesion is benign with no malignant potential.
- Once metallic particles are confirmed radiographically (or after histopathologic diagnosis), no further intervention is needed.
- For esthetic concerns, removal options include surgical (cold steel) excision, low-energy laser removal, and subepithelial connective tissue grafts with laser de-epithelialization or gingivoplasty.