Iron staining of the acquired enamel pellicle after exposure to tannic acid or chlorhexidine: preliminary report

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Abstract
Extrinsic discoloration of teeth following a large consumption of tannin-containing beverages or a prolonged use of chlorhexidine mouth rinses is a well known observation. Tannins as well as chlorhexidine are denaturing agents. Based on preliminary studies revealing the presence of Fe in chlorhexidine-discolored pellicle material, the ability of Fe to stain the integument after pretreatment with the 2 denaturants was studied in a human model. The denaturing effect of an acidic environment was also included. Enamel slabs fixed to acrylic appliances were carried in the oral cavity and alternately exposed to the test solutions in different sequences in vitro. Pretreatment with chlorhexidine or tannic acid led to marked discolorations upon Fe application during 5-day tests, whereas the compounds individually had no such effect. A large content of the metal was found in the stained material. Stannous fluoride appeared to reduce the formation of the pigments, and strong oxidation completely bleached the established color. Possible mechanisms underlying the phenomena observed are discussed.