Mechanisms of Stain Formation on Teeth, in Particular Associated with Metal Ions and Antiseptics

Abstract

Much has been written on the subject of extrinsic tooth discoloration, but, except when the pigment is intentionally applied, the etiologies and mechanisms are poorly understood. Extrinsic stains have been classified as non-metallic or metallic. The pigment usually lies not on or in the dental tissues, but in surface deposits, particularly the acquired pellicle layer and at sites receiving limited cleaning. Whether pigments absorb, adsorb, or chemically interact with dental surfaces is unclear. Some stains merely seem to reflect the color of the apparent source, whereas others have been ascribed to a secondary chemical alteration of a substance at the tooth or pellicle surface. Theories of chromogenic bacteria and formation of metal sulfides are frequently propounded but without clear supportive evidence. Staining by cationic antiseptics and, to a lesser extent, metal salts has attracted research interest. Chlorhexidine and other cationic antiseptics, it is hypothesized, may catalyze browning reactions or facilitate metal sulfide formation in pellicle. Controlled clinical studies have repeatedly shown that dental and mucosal staining associated with the use of chlorhexidine and some metal salts is dependent upon volunteers' imbibing reasonable quantities of chromogenic beverages, such as tea. However, it must be appreciated that cationic antiseptics and polyvalent metals can precipitate chromogenic material from a large range of dietary compounds. The control of dental staining, at least that associated with chlorhexidine, can be achieved both in vitro and in vivo by the use of oxidizing agents which appear to remove the stain physically from the surfaces.

Tooth discolouration and staining: a review of the literature

“…Thus, polyphenols found in dietary substances, being anionic, are able to react with cations adsorped to surfaces such as the cationic antiseptics or polyvalent metal ions to produce staining. 7 The difference in the potential of various cationic antiseptics to produce staining in vivo can be explained by their differing substantivity, which is consistent with the dietary aetiology. The apparent individual variation in staining noted in particular with chlorhexidine is of interest.…”

“…55 Most recent debate has centred around three possible mechanisms. 7 Non-enzymatic browning reactions: Berk suggested that the protein and carbohydrate in the acquired pellicle could undergo a series of condensation and polymerisation reactions leading to discolouration of the acquired pellicle. 57 Chlorhexidine may accelerate formation of the acquired pellicle 58 and also catalyze steps in the Maillard reaction.…”

The chemical stain removal properties of 'whitening' toothpaste products: studies in vitro

“…Such causes of discoloration are usually classified as intrinsic or extrinsic staining respectively; signifying the source of the stain. [1][2][3] Clearly, some extrinsic stains can become internalised through enamel defects or cracks or as a result of dentine becoming exposed. 2,3 Most extrinsic stains appear to be deposited on or in the acquired pellicle.…”

“…4 Furthermore, the dental staining associated with the cationic antiseptics and polyvalent metal salts appears to arise from an interaction and precipitation reaction with dietary chromogens. 2,5,6 Attempts to improve the colour of teeth could be directed against either intrinsic or extrinsic stains, or by changing the natural colour of the teeth. To date changing the natural colour of teeth or removing intrinsic discoloration has relied mainly on bleaching agents such as carbamine peroxide.…”

“…[1][2][3] Clearly, some extrinsic stains can become internalised through enamel defects or cracks or as a result of dentine becoming exposed. 2,3 Most extrinsic stains appear to be deposited on or in the acquired pellicle. The aetiology of such discoloration is poorly understood but compounds within the diet or from tobacco are considered the most common chromogens.…”