This invention relates to a sodium bicarbonate-containing tooth powder.  More particularly, this invention relates to a tooth powder containing sodium bicarbonate particles of particular sizes, which powder has been found to exhibit improved flavor, flow and abrasivity characteristics as compared with prior tooth powders containing commercial baking powder. 
Many different dentifrice compositions are known for cleaning, whitening, and preserving the teeth.  Many of these dentifrice compositions include a high content of water-insoluble abrasives, such as dicalcium phosphate, which aid in preventing pellicle and stain build-up on the teeth.  In order to preserve the teeth as much as possible, it is widely accepted that the least abrasive material necessary to remove plaque and stain should be used in dentrifrice compositions. 
Most dentifrices formulated today are in the form of a paste, gel or powder.  Toothpastes and gels generally contain, in addition to the abrasive material, humectants, water, thickeners, surfactants, flavors and sweeteners.  Tooth powders generally contain only abrasives, flavor, sweetener and sometimes a surfactant.  Both types of products sometimes contain additional ingredients for special functional or aesthetic reasons, for example, fluoridating or coloring agents. 
Toothpastes and gels have gained wider consumer acceptance than powders since they tend to be more convenient to use.  However, powder formulations have certain advantages over toothpastes.  For example, humectants, thickeners and water serve no useful purpose in the actual cleaning of teeth but are needed to provide stability to the desired paste or gel form.  Powders do not require these ingredients. 
One drawback of pastes and gels is the cost of the non-cleaning ingredients.  Pastes and gels usually contain 20-50% humectant and thickener, representing a disproportionate share (30%-50%) of the cost of the finished toothpaste or gel.  Tooth powders, which may contain up to 99% useful abrasive materials, eliminate the need for the costly (non-cleaning) humectant and thickener ingredients. 
A further drawback of pastes and gels is the difficulty of ensuring that these products have the right consistency, are stable and that the ingredients are compatible.  Tooth powders, in contrast, are much easier to formulate. 
Baking soda particles are relatively soft as compared to most conventional abrasive materials used in dentifrice compositions.  The American Dental Association has recommended that "if only a slight degree of abrasion is necessary to keep from staining, baking soda will usually be found satisfactory."  Accepted Dental Therapeutics, pp.  340-341 (38th Ed.,  1979).  Toothpaste formulations containing sodium bicarbonate particles as a cleansing agent for teeth have been previously disclosed.  See, for example, U.S. Pat.  No.  3,943,240 (Delaney et al) and similar patents which disclose a toothpaste composition containing at least about 20%, preferably at least about 30% sodium bicarbonate particles.  The size of the sodium bicarbonate particles in the disclosed toothpaste compositions may vary; but it is preferred that a major portion of the particles be above 0.01 mm and below 0.4 mm in diameter.  U.S. Pat.  No.  2,128,917 (Crocker) also discloses a sodium bicarbonate-containing toothpaste.  Crocker discloses that the sodium bicarbonate comprises close to 50% by weight of the toothpaste and that the sodium-bicarbonate particles may be sifted through a #200 mesh sieve (74 microns). 
Formulation stability is a frequent problem with sodium bicarbonate-containing pastes or gels.  Sodium bicarbonate is unstable in an aqueous solution and releases carbon dioxide gas.  See, e.g., U.S. Pat.  No.  3,943,240 at column 1, lines 32-34.  Also, sodium bicarbonate is not always compatible with other abrasive materials in pastes and gels.  See, e.g., U.S. Pat.  No.  3,943,240 at column 2, lines 58-62.  In contrast, sodium bicarbonate is stable as a dry powder and is compatible in almost any proportion with most other dry ingredients.  Thus, sodium bicarbonate-containing tooth powders have decided advantages over sodium bicarbonate-containing toothpastes or gels. 
In addition to the above advantages of a sodium bicarbonate-containing tooth powder, it is possible to formulate a tooth powder having a much higher proportion of sodium bicarbonate than is possible in toothpastes or gels.  Sodium bicarbonate gives a clean, fresh feeling to the mouth.  Sodium bicarbonate also helps to deodorize the oral cavity by neutralizing acidic odors.  Thus, it is desirable to maximize the sodium bicarbonate content of a dentifrice.  However, because of stability problems, it is difficult, if not impossible, to provide more than about 60% sodium bicarbonate in a paste or gel and maintain the product in usable form.  A tooth powder, however, may contain higher levels of sodium bicarbonate. 
Thus, it is desirable to provide a dentifrice in the form of a tooth powder in which a major proportion of the ingredients comprises sodium bicarbonate particles. 
Several tooth powders containing sodium bicarbonate particles have been previously described. 
U.S. Pat.  No.  1,082,681 (Danner), for example, discloses a tooth powder containing agglomerated sodium bicarbonate granules having a fineness of about #30 mesh sieve (595 microns) which break down into powdered form in the mouth.  The granular particles are produced by moistening with water, sieving and drying.  Such a product has an excessively granular feel in the mouth.  Moreover, as a result of the pre-moistening and drying some decomposition of the bicarbonate occurs, the resulting material having a slightly bitter taste. 
U.S. Pat.  No.  2,024,146 (Crowther) discloses a tooth powder containing about 15% by weight of sodium bicarbonate, about 30% and two other more abrasive materials (magnesium oxide and calcium carbonate), and at least 12 other ingredients.  The tooth powder passes through a #40 mesh sieve (420 microns). 
U.S. Pat.  No.  4,276,287 (Cabardo, Jr.) discloses a periodontal powder containing about 2/3 potassium alum and 1/3 sodium bicarbonate, together with small quantities of antiseptics, flavoring agents, sweenteners and colorants.  The particle size range of the sodium bicarbonate powder constituent is not specified in the patent.  Moreover, because of the strongly acidic, astringent flavor of the alum, the degree of granulation of the minor quantity of the sodium bicarbonate present in the tooth powder would have not effect on the taste or mouth feel of this product. 
The multipurpose baking soda of commerce is also recommended for use as a tooth powder; such material consists essentially of sodium bicarbonate particles having a median particle size in the range of 44-73 microns. 
One major problem encountered in the formulation of a tooth powder having a major proportion by weight of abrasive particles, including sodium bicarbonate particles, is reducing the abrasiveness of the tooth powder to acceptable levels.  Excessive abrasiveness can lead to loss of tooth enamel and erosion of exposed dentin.  Abrasiveness is of particular concern in tooth powders since the concentration of abrasives is much higher than in pastes or gels.  Also, the ingredients present in the pastes and gels often serve to moderate the abrasivity of the overall formulation. 
Another major problem encountered in formulating a tooth powder containing sodium bicarbonate particles is the salty taste of sodium bicarbonate.  It has now been found that the salty flavor decreases and can be more readily masked if coarser grades of sodium bicarbonate are used in the tooth powder.  In order to prepare a sodium bicarbonate-containing dentifrice which is not too salty, the use of large sodium bicarbonate particles is indicated.  However.  it is known that abrasivity generally increases with increasing particle size.  See, for example, Cosmetic Science and Technology, Vol.  1, pages 427, 428 (Wiley-Interscience, 2d Ed.,  1972); Tainter, M. L., and S. Epstein, 30 J. Am.  Dent.  Assoc.,  pp.  1036-1045 (1943); M. L. Smith, J. Soc.  Chem.  Ind., pp.  691-697 (Aug. 23, 1935).  Thus, with the higher levels of sodium bicarbonate pesent as the principal abrasive in a tooth powder, one would except that a significant increase in the mean particle size would increase the abrasivity. 
In accordance with the present invention, a sodium bicarbonate-containing tooth powder is provided which is effective in preventing pellicle and stain build-up on the teeth, but is not so abrasive as to deleteriously affect tooth enamel, cementum, or dentin.  Moreover, and notwithstanding prior expectations, the sodium bicarbonate particles are sufficiently coarse so that the tooth powder is not excessively salty but leaves the user with a fresh mouth taste.