1. Field of the Invention
The present invention relates to a dentifrice composition which has a caries-preventing effect that is maintained for a long time. More particularly, the invention relates to a fluorine-containing dentifrice composition in which the reduction of the content of water-soluble fluoride material with the passage of time is prevented by incorporating montmorillonite or hectorite having a specific composition, into the dentifrice composition.
2. Description of the Priot Art
Fluorine is now considered to be the most effective of the currently available caries-preventing agents. Sodium fluoride, sodium monofluorophosphate, stannous fluoride and the like are conventionally incorporated into dentifrices for this purpose. It is generally considered that fluorine ions react with hydroxyapatite in the tooth enamel to form fluoroapatite, whereby the dentin is hardened, the acid resistance of the dentin is enhanced and the resistance of the dentin against attacks of bacteria and acids is increased. According to another theory, it is said that fluorine ions prevent bacteria from adhering to the tooth surfaces. Although a definitive theory has not been established as regards the caries-preventing effect of fluorine ions, by various clinical tests it has been confirmed that fluorine ions have an excellent caries-preventing effect.
A polishing agent such as calcium phosphate dibasic anhydride (CaHPO.sub.4), its dihydrate (CaHPO.sub.4.2H.sub.2 O), calcium carbonate, calcium pyrophospate and/or other calcium salts are incorporated in dentifrices in an amount of about 50 vol. % of the total dentifrice. Calcium ions become dissolved in a dentifrice in a minute amount and gradually react with fluorine ions to form water-insoluble calcium fluoride which has no caries-preventing effect. Accordingly, the caries-preventing effect of a fluorine ion-containing dentifrice is gradually reduced with the passage of time.