Synthetically produced precipitated silicas play an important role as an ingredient in many of today's toothpaste formulations. In addition to their cleaning ability, they are also relatively safe, nontoxic, and compatible with other toothpaste ingredients, including glycerin, sorbitol (or xylitol), thickening agents, detergents coloring and fragrance materials and, optionally, fluoride containing compositions.
Synthetic precipitated silicas are prepared by admixing alkaline silicate solutions with acids, stirring and then filtering out the precipitated silica. The resulting precipitate is next washed, dried and comminuted to desired size. When preparing synthetic precipitated silicas, the objective is to obtain silicas which provide maximal cleaning with minimal damage to oral tissue. Dental researchers are continually concerned with identifying precipitated silicas meeting these objectives.
Examples of precipitated silicas include U.S. Pat. No. 4,122,161 to Wason, Oct. 24, 1978, U.S. Pat. Nos. 4,992,251 and 5,035,879 to Alderoff et al., Feb. 12, 1991 and Jul. 30, 1991 respectively, U.S. Pat. No. 5,098,695 to Newton et at., Mar. 24, 1992, and U.S. Pat. No. 5,279,815 to Wason et al., Jan. 18, 1994.
Moreover, various combinations of silicas have also been described in the art. Silica combinations involving compositions of differing particle sizes and specific surface areas are disclosed in U.S. Pat. No. 3,577,521 to Karlheinz Scheller et al., May 4, 1971 and U.S. Pat. No. 4,618,488 to Maeyama et al., Oct. 21, 1986, respectively. Similarly, U.S. Pat. Nos. 5,110,574 to Reinhardt et al., May 5, 1992 discloses combining thickener and polishing silicas to form silica compositions having oil absorption values of at least 200. Further examples of silica combinations include U.S. Pat. No. 5,124,143 to Muhlemann, Jun. 23, 1992 and U.S. Pat. No. 4,632,826 to Ploger et al., Dec. 30, 1986.
In spite of the many disclosures relating to compositions for oral cleaning and antiplaque activity, there is still a need for additional compositions providing improved pellicle cleaning with minimal abrasion. The present inventor has discovered that abrasive compositions comprising silicas having particles of differing hardness values provide improved dental cleaning with minimal abrasion.
Accordingly, it is the object of the present invention to provide precipitated silica compositions exhibiting improved pellicle cleaning without a corresponding increase in dentin or enamel abrasion. Another object of the present invention is to provide an effective method for the prevention or removal tooth stains. A further object of the present invention is to provide an effective method for the prevention or removal of plaque. These and other objects will become readily apparent from the disclosure which follows.