Are there metallic traces in black extrinsic dental stain?

Objective: The detection of ferric ions in samples of black extrinsic dental stain led to the idea that it is comprised of insoluble ferric compounds. The present study examined the chemical composition of black extrinsic dental stain.
Method and Materials: Plaque was collected from 17 children with black extrinsic dental stain (study group A) and from 15 children without black extrinsic stain (control group), using sterile graphite curettes; and from 4 children with black extrinsic stain (study group B), using a standard sterile metal curette. Samples were analyzed with a scanning electron microscope (SEM) and subjected to quantitative chemical analysis (energy dispersive spectrometry).
Results: Except for calcium and phosphorus levels, no significant differences were found between the chemical composition of black extrinsic dental stain and dental plaque. Metallic ions were not detected in samples collected with a graphite curette (study group A), but were detected in samples collected with a metal curette (study group B).
Conclusion: Metallic ions do not seem to be the origin of black extrinsic dental stain. Previous reports of the presence of metallic ions are probably due to contamination of the samples by the collection method.