Abstract
Pigmentation of the oral mucosa is relatively common and has a wide variety of etiologies. Although most pigmented lesions of the oral mucosa are associated with deposition of melanin and accidental displacement of a dental alloy, accurate differential diagnosis of a pigmented lesion is important, especially in the case of malignant melanoma. We report two cases of oral mucosal pigmentation associated with accidental displacement of a dental alloy in which malignant melanoma was suspected. Excisional biopsy was carried out in these cases with the incision line set at approximately 5 mm from the lesions. Histopathologically, brownish foreign substances were observed in the lamina propria. Metal quantitative analyses of the extracted specimens were carried out by electron probe microanalysis (EPMA). The metal components and the mass concentration revealed that the metals were derived from a dental casting silver alloy in Case 1 and from a gold-silver palladium alloy in Case 2. Although exogenous pigmentation originating from a dental alloy is not rare, differential diagnosis of oral pigmented lesions is sometimes very difficult. In such cases, histopathological examination may be necessary for the diagnosis to exclude melanocytic lesions and EPMA may be effective to identify the causative dental alloy.
Highlights
Pigmentation of the oral mucosa is distinguished as either endogenous or exogenous
Most pigmented lesions of the oral mucosa are associated with deposition of melanin and accidental displacement of a dental alloy, accurate differential diagnosis of a pigmented lesion is important
It is important to differentiate between pigmented nevus caused by the proliferation of nevus cells and malignant melanoma derived from melanocytes
Summary
Pigmentation of the oral mucosa is distinguished as either endogenous or exogenous. The causes of each are endogenous pigments of melanin, hemosiderin, or bilirubin and exogenous pigments of metal or medical agents [1]. Most pigmented lesions of the oral mucosa are associated with deposition of melanin and accidental displacement of a dental alloy, accurate differential diagnosis of a pigmented lesion is important. We report two cases of oral mucosal pigmentation associated with accidental displacement of a dental alloy in which malignant melanoma was suspected and excisional biopsy and electron probe microanalysis were carried out. Three dark lesions were observed in the oral mucosa around the right lower wisdom tooth (Figure 1). Excisional biopsy for differential diagnosis was carried out with extraction of the right lower wisdom tooth and integral excision of the three lesions including the periosteum with a safety margin of approximately 5 mm from the dark lesions (Figure 3). One month post-operatively, the area had healed normally and the last follow-up with the patient was 3 months after the surgery uneventfully
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