Dentifrice Compositions

The invention relates to dentifrice compositions.

According to the present invention, there is provided a dentifrice composition containing synthetic hydroxyapatite powder and being neutral or weakly alkaline.

It has been found that the dentifrice composition of the present invention is very effective in fortifying a surface of a tooth, promoting remineralization of the surface of the tooth and eliminating plaque (a colony of bacteria).

In general, a conventional dentifrice contains, as a tooth-cleaning and abrading agent, a mineral, such as colloidal silica, calcium phosphate, calcium carbonate, magnesium carbonate, etc. While these abrading agents are used to remove contaminants on teeth, it is essential that they do not harm the teeth.

Since the dentifrice composition of the present invention contains a suitable amount of synthetic hydroxyapatite powder, plaque as well as substances contaminating teeth can be removed very effectively. We presume this is due to the fact that the synthetic hydroxyapatite has a hardness similar to that of the enamel portion of the tooth and it can impart an appropriate abrading effect on the enamel portion of the tooth in brushing the teeth. We further presume this is also due to the fact that the synthetic hydroxyapatite has a large surface area and an excellent absorptivity. We have further found that the synthetic hydroxyapatite powder has the effect of strengthening the coating on and remineralization the surface of the enamel of the tooth.

In accordance with the present invention, there is further provided a dentifrice composition containing synthetic hydroxyapatite powder and, based on the weight of the composition, 0.1 to 20% by weight of NaCl and/or KCl and 0.003 to 3% by weight of MgCl.sub.2.

It has also been found that the presence of a mixture of NaCl and/or KCl with MgCl.sub.2 in a dentifrice composition containing synthetic hydroxyapatite powder can effectively promote the elimination of plaque from teeth and the fortification and remineralization of the surfaces of the teeth.

More specifically, the latter dentifrice composition of the present invention can effectively deposit and coat crystals of hydroxyapatite on the surfaces of the teeth. We presume this is due to the fact that the solubility of hydroxyapatite in water is increased in the presence of the chlorides as specified above. More particularly, since hydroxyapatite is a salt which only slightly soluble in water, the ion products of ions such as [Ca.sup.++ ], [HPO.sub.4.sup.-- ], etc. ionized in the dentifrice are small. This means that the ion products for promoting coating on the surfaces of the teeth, i.e. deposition of the crystals of hydroxyapatite on the surfaces of the teeth are small. However, if NaCl and/or KCl and MgCl.sub.2 are added to the dentifrice containing hydroxyapatite, it is presumed that the solubilities of Ca.sup.++ and HPO.sub.4.sup.-- are increased very much and the coating on the teeth is enhanced.

In cases where the amounts of NaCl and/or KCl and MgCl.sub.2 contained in the dentifrice composition of the present invention are smaller than those specified above, a sufficient coating effect cannot be obtained, while in cases where such amounts are larger than those specified above, it becomes difficult to give a comfortable feeling in the use of the dentifrice composition.

To obtain a suitable abrading effect and desired plaque elimination, the average particle size of the hydroxyapatite powder is preferably about 2.mu. and the maximum particle size thereof is preferably 10.mu. or less.

The dentifrice composition of the present invention may include various additives which are commonly employed in dentifrices and may further include, if desired, citric acid, lactic acid, acetic acid, pyrrolic acid, glutamine, proline, serine, glycine, etc.

The invention will be further illustrated with reference to the following examples. Examples 1 to 7 and 11 to 17 respectively show formulations of the dentifrice compositions in accordance with the present invention in terms of parts by weight and Examples 8 to 10, 18 and 19 are to substantiate effects of the composition of the present invention.

0.1% solution of Neutral Red was applied to the front teeth of each of three male adults A, B and C (22 to 25 years old), who had been using conventional commercially available dentifrices. Thereafter, similar dyeing operation was conducted one day after they started to use the dentifrice of Example 1 and the plaque-stained areas before and after the change of the dentifrices were compared. In the case of A, the stained area after the change was about 10% of the initial stained area and it was confirmed that the decontamination of the plaque area was about 90%. In cases of B and C, the decontamination of the plaque areas was about 50%.

Abrasive effects of dentifrices were tested using, for teeth, plate-form bodies made of sintered hydroxyapatite having a hardness similar to that of an enamel portion of a tooth. The plate-form bodies were each subjected to brushing using tooth brushes and different dentifrices for 60 minutes. The losses in weights of the respective plate-form bodies were measured. In the result, the abrasive effects of the dentrifrice composition of the present invention was similar to those of commercially available dentifrices (WHITE & WHITE and DENTER LION).

An adult's permanent tooth was sliced in two using a prisma adamantinum to form a section having a thickness of about 200 .mu.m. A supernant saturated solution of a liquid prepared by stirring 1 g of hydroxyapatite powder with 100 ml of distilled water was passed over the thus formed section at a flow rate of 0.6 ml/min. The section was observed continuously using a polarization microscope and it was confirmed that the section was coated with analogous apatite crystals about 1 .mu.m thick after 14 hours.

1 g of hydroxyapatite powder was introduced into 100 ml of 37.degree. C. distilled water and NaCl and MgCl.sub.2 were added in various concentrations. The calcium ion concentrations of the respective solutions were measured and it was confirmed that the solubility of hydroxyapatite was increased by adding NaCl and MgCl.sub.2. The calcium ion concentrations 10 days after the preparation of the solutions were as follows:

An adult's permanent tooth was sliced in two using a prisma adamantinum to prepare a section about 200 .mu.m thick. The enamel portion was removed to expose the dentin portion. A hydroxyapatite-saturated solution in distilled water containing 0.001% of MgCl.sub.2 and 0.9% of NaCl was passed over the so prepared section at a flow rate of 0.6 ml/min. The section was continuously observed using a polarization microscope and it was confirmed that all over the surfaces of the section were coated with analogous apatite crystals at a thickness of about 5 .mu.m.