RU2798833C2 - Size of spherical silicon dioxide particles intended for regulation of ird - Google Patents

Abstract

FIELD: dental care products.

SUBSTANCE: silicon dioxide particles with a median particle size d50 of 8.8 to 15 µm; the value of the ratio (d90-d10)/d50, equal to from 1.1 to 2.0; the value of RDI when the content of particles of silicon dioxide in the composition of the toothpaste, constituting 20 wt.% ranging from 70 to 200; oil absorption in the range from 30 to 62 cm³/100 g; a bulk density after compaction ranging from 52 to 65 lb/ft³; the value of the cleaning index from the film (POP) at a content of 20 wt.% ranging from 80 to 110; and a sphericity coefficient (S₈₀) greater than or equal to 0.9 are proposed. Also a toothpaste and dentifrice compositions comprising the said silica particles, and a method for producing the said particles are proposed.

EFFECT: obtained particles of silicon dioxide have a reduced degree of abrasion of radioactive dentin (IRD).

19 cl, 13 dwg, 6 tbl, 13 ex

Description

BACKGROUND OF THE INVENTION

The Relative Dentin Abrasion Test (RDA, this test is commonly referred to as Radioactive dentin abrasion - The Radioactive Dentin Abrasion Test (RDA), which will be used below) is a test that is used to establish safe limit values for toothpaste and other compositions. for dental care. The IRD test involves determining the loss of dentin after brushing with the test toothpaste composition, based on the value for calcium pyrophosphate as a control (set to 100).

Unlike conventional non-spherical and irregularly shaped silica particles, spherical silica particles have some characteristics (such as a low Einlechner abrasion value) that are favorable for use in toothpaste and other dentifrices. However, it would be preferable that these spherical silica materials also provide improved IRD performance. Accordingly, this is basically the object of the present invention.

SUMMARY OF THE INVENTION

This Summary is intended to introduce, in a simplified form, some of the concepts that are further described below in the Detailed Description of the Invention. This summary is not intended to establish necessary or important features of the claimed subject matter. This summary is also not intended to limit the scope of the claimed subject matter.

The present invention discloses and describes silica particles that provide a reduced degree of radioactive dentin abrasion (RAD). In accordance with one embodiment of the present invention, such silica particles may have (i) a median particle size d50 greater than or equal to about 6 microns, (ii) a (d90-d10)/d50 ratio value ranging from about 1.1 up to about 2.4, (iii) the value of IRD at a content of 20 wt. % ranging from about 40 to about 200, and (iv) a sphericity coefficient (S ₈₀ ) greater than or equal to about 0.9. These silica particles have a spherical shape or morphology and can be produced using a continuous loop reactor.

The present invention also discloses dentifrice compositions containing silica spherical particles, typically in amounts in the range of 0.5-50 wt. %, and more often in the range of 5-35 wt. %.

The present invention also discloses methods for producing silica particles, and one such method may include (a) continuously feeding the inorganic acid and alkali metal silicate into a loop reaction zone containing a liquid medium stream in which at least a portion of the inorganic acid and alkali metal silicate enter reacting to form silica particles in the liquid medium contained in the loop reaction zone, (b) continuously recirculating the liquid medium through the loop reaction zone, and (c) continuously discharging from the loop reaction zone a portion of the liquid medium containing the silica particles. Preferably, if steps (a)-(c) can be carried out under low or no shear conditions, this unexpectedly results in more round and more spherical particle morphology. Thus, for example, the loop reaction zone may not include a stator screen, or the loop reaction zone may include a stator screen with holes having a cross-sectional area greater than 3 mm ² . Additionally or alternatively, the shear rate in the loop reaction zone may be less than 1,000,000 interactions/min.

Both the foregoing summary and the following detailed description of the invention provide examples and are illustrative only. Accordingly, the foregoing summary and the following detailed description of the invention should not be considered limiting. In addition, there may be features and options, additional to those given in the present invention. Thus, for example, some embodiments may refer to various combinations and subcombinations of the features described in the Detailed Description of the Invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 is a scanning electron micrograph of the silica of Example 1A.

In FIG. 2 is a scanning electron micrograph of the silica of Example 2A.

In FIG. 3 is a diagram of the loop reactor apparatus used to prepare the silica products of Examples 3A-8A.

In FIG. 4 is a scanning electron micrograph of the silica of Example 3A.

In FIG. 5 is a scanning electron micrograph of the silica of Example 4A.

In FIG. 6 is a scanning electron micrograph of the silica of Example 5A.

In FIG. 7 is a scanning electron micrograph of the silica of Example 6A.

In FIG. 8 is a scanning electron micrograph of the silica of Example 7A.

In FIG. 9 is a scanning electron micrograph of the silica of Example 8A.

In FIG. 10 shows a model for a 4 µm spherical particle interacting with a 2.5 µm dentinal tubule.

In FIG. 11 shows a model for spherical particles of increasing size (4 µm, 5 µm, 6 µm, 10 µm) interacting with a 2.5 µm dentinal tubule.

In FIG. 12 shows the dependence of the depth of penetration of a particle into a dentinal tubule with a width of 2.5 μm on the diameter of the particle if it has a spherical shape.

In FIG. 13 shows the dependence of the force required to roll out a sphere from a 2.5 μm wide tubule on the particle diameter in case it has a spherical shape.

DEFINITIONS

For a more precise definition of the terms used in the present invention, definitions are given below. Unless otherwise indicated, the following definitions apply to the present description. If a term is used in the present invention but is not specifically defined in the present invention, then the definition given in the IUPAC Compendium of Chemical Terminology, 2nd Ed (1997) may be used, unless such definition conflicts with any other disclosure or definition used herein. invention, or it does not render indefinite or invalidate any claim to which this definition relates. To the extent that any definition or use provided by any document incorporated herein by reference conflicts with the definition or use provided herein, the definition or use provided herein shall govern.

In the present invention, the features of an object are described so that a combination of different features can be provided for in particular embodiments. For each embodiment and each feature disclosed in the present invention, all combinations that do not adversely affect the drawings, compositions, methods or technologies described in the present invention are within the scope of the present invention and they can be interchanged with or without explicit descriptions of a specific combination. Accordingly, unless expressly stated otherwise, any embodiment or feature disclosed in the present invention may be combined to describe the drawings, compositions, methods, or techniques of the present invention consistent with the present invention.

Although compositions and methods are described herein using the terms "comprising" various components or steps, compositions and methods may also "consist essentially of" or "consist of" various components or steps, unless otherwise indicated.

Singular terms are intended to include plural terms, such as at least one, unless otherwise noted.

Typically, groups of elements are indicated using the numbering scheme given in the variation of the Periodic Table of the Elements given in Chemical and Engineering News, 63(5), 27, 1985. In some cases, a group of elements may be indicated using the common name assigned to the group; for example, alkali metals for group 1 elements, alkaline earth metals for group 2 elements, and the like.

While any techniques and materials similar to or equivalent to those described herein may be used in the practice or testing of the present invention, exemplary techniques and materials are described in the present invention.

All publications and patents noted in the present invention are incorporated into the present invention by reference to describe and disclose, for example, the concepts and methodologies that are described in publications that can be used in connection with the described present invention.

Several types of ranges are disclosed in the present invention. If a range of any type is disclosed and claimed, every possible number that is reasonably within such range is disclosed and claimed, including the end points of the range, as well as any subranges and combinations of subranges contained therein. As a typical example, note that the BET surface area (specific surface area determined by the Brunauer-Emmett-Teller method) of silica particles can be in certain ranges in various embodiments of the present invention. By indicating that the BET surface is in the range of from about 20 to about 100 m ² /g, it is understood that the surface can be any surface in this range and, for example, can be equal to about 20, about 30, about 40, about 50, about 60, about 70, about 80, about 90 or about 100 m ² /g.

In addition, the surface can be in any range from about 20 to about 100 m ² /g (for example, from about 45 to about 85 m ² /g) and this also includes any combination of ranges from about 20 to about 100 m ² /g (for example, the surface may range from about 20 to about 50 m ² /g, or from about 70 to about 90 m ² /g). Similarly, all other ranges disclosed in the present invention should be interpreted in the same way as in this example.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally discloses spherical silica particles that can be characterized by (i) a median particle size d50 greater than or equal to about 6 microns, (ii) a (d90-d10)/d50 ratio ranging from about 1.1 up to about 2.4, (iii) the value of IRD at a content of 20 wt. % ranging from about 40 to about 200, and (iv) a sphericity coefficient (S ₈₀ ) greater than or equal to about 0.9. The present invention also discloses methods for producing these spherical silica particles and dentifrice compositions containing spherical particles.

SPHERICAL SILICON DIOXIDE PARTICLES

According to embodiments of the present invention, spherical silica particles providing improved IRD performance may have the following characteristics: (i) a median particle size d50 greater than or equal to about 6 microns, (ii) a (d90-d10)/d50 ratio value in the range from about 1.1 to about 2.4, (iii) the value of IRD at a content of 20 wt. % ranging from about 40 to about 200, and (iv) a sphericity coefficient (S ₈₀ ) greater than or equal to about 0.9. In other embodiments, such silica particles of the present invention may also have any of the characteristics or any of the properties below, and any combination thereof.

In one embodiment, the spherical silica particles may have a relatively large average particle size. The median particle size (d50) and/or average particle size (average) can often range from about 6 to about 30, in a preferred embodiment from about 6 to about 25, in a more preferred embodiment from about 6 to about 20, in a more preferred embodiment, from about 7 to about 25, in a more preferred embodiment, from about 7 to about 20, and in a more preferred embodiment, from about 7 to about 18 microns. In another embodiment, the median particle size (d50) and/or average particle size (average) may range from about 8 to about 25, in a preferred embodiment from about 8 to about 20, in a more preferred embodiment from about 8 to about 18, and in a more preferred embodiment, from about 8 to about 15 microns. Other suitable ranges for mean and median particle sizes will be apparent from the present disclosure.

The spherical silica particles can also have a very narrow particle size distribution, which can be quantified using the ratio (d90-d10)/d50. A lower ratio value indicates a narrower particle size distribution, while a higher ratio value indicates a wider particle size distribution. The spherical particles of the present invention may typically have a (d90-d10)/d50 ratio ranging from about 1.1 to about 2.4. In one embodiment, the value of the ratio (d90-d10)/d50 may range from about 1.1 to about 2.2, while in another embodiment the value of the ratio (d90-d10)/d50 may range from about 1 .1 to about 2. In addition, in another embodiment, the value of the ratio (d90-d10)/d50 may be in the range from about 1.2 to about 2.4, while in another embodiment, the value of the ratio (d90-d10 )/d50 may range from about 1.2 to about 2.2, and in a more preferred embodiment, from about 1.2 to about 2. Other suitable ranges for the value of the ratio (d90-d10)/d50 are apparent from the present description.

The Radioactive Dentin Abrasion Test (RAT) is typically performed to confirm that a dentifrice composition, such as toothpaste, is safe for consumer use, with an upper limit of 250 in this test. The results of the present invention surprisingly show that for the spherical silica particles of the present invention, the RDI generally decreases with increasing median particle size (d50) and/or average particle size (averaged). In one embodiment of the present invention, the spherical particles of silicon dioxide may differ in the value of IRD at a content of 20 wt. %, ranging from about 40 to about 200, and in another embodiment, from about 50 to about 190. Other illustrative and non-limiting examples of ranges for RDI values at a content of 20 wt. % may include a range of from about 70 to about 200, in a preferred embodiment from about 70 to about 170, in a preferred embodiment from about 85 to about 180, and in a more preferred embodiment from about 100 to about 160. Other suitable ranges for the RDI values are obvious from the present description.

The sphericity of the spherical silica particles can be quantified by the sphericity factor (S ₈₀ ), which is typically greater than or equal to about 0.85, in a preferred embodiment greater than or equal to about 0.88, and in a more preferred embodiment greater than or equal to about 0, 9. The sphericity coefficient (S ₈₀ ) is determined as follows. The SEM (Scanning Electron Microscope) image of a silica particle, which is typical of a sample of a silica particle, is magnified by 20,000 times and transferred to an image processing software and outlines each particle (two-dimensionally). In this analysis, particles that are close to each other, but not connected to each other, are considered separate particles. The circled particles are then filled in and the image is passed to particle characterization software (eg, IMAGE-PRO PLUS, available from Media Cybernetics, Inc., Bethesda, Md.), which can determine particle perimeter and area. The sphericity of the particles can then be determined from the equation, sphericity = (perimeter) / (4π×area), where perimeter is the software-defined perimeter of the traced particle outline, and where area is the software-defined area inside the traced particle perimeter.

The sphericity evaluation is carried out for each particle that is entirely located in the SEM image. These values are then sorted and the smallest values that make up 20% of these values are discarded. The remaining 80% of these values are averaged and the sphericity coefficient (S ₈₀ ) is obtained. Additional information regarding sphericity is provided in US Pat. Nos. 8,945,517 and 8,609,068, incorporated herein by reference in their entirety.

In one embodiment of the present invention, the spherical silica particles may have a sphericity coefficient (S ₈₀ ) greater than or equal to about 0.85, in another embodiment greater than or equal to up to about 0.88, and in a more preferred embodiment greater than or equal to about 0 ,9. In addition, in another embodiment, the spherical silica particles may have a sphericity factor (S ₈₀ ) greater than or equal to about 0.92, and in another embodiment, the silica particles may have a sphericity factor (S ₈₀ ) greater than or equal to about 0.94. It should be obvious to one skilled in the art that a 3-dimensional sphere (or 2-dimensional circle) has a sphericity factor (S ₈₀ ) of 1.

The spherical silica particles may have any suitable surface area, typically a BET surface ranging from about 10 to about 200 m ² /g. The BET surface can often range from about 20 to about 200, in a preferred embodiment from about 20 to about 180, and in a more preferred embodiment from about 20 to about 160 m ² /g. In other embodiments, the BET surface may range from about 20 to about 130, in a preferred embodiment from about 20 to about 100, in a more preferred embodiment from about 30 to about 180, in a more preferred embodiment from about 30 to about 160, in a more preferred embodiment from about 30 to about 100, in a more preferred embodiment from about 40 to about 180, and in a more preferred embodiment from about 40 to about 80 m ² /g. Other suitable ranges for the BET surface will be apparent from the present description.

In addition, the spherical silica particles may be less abrasive, as indicated by an Einlechner abrasion index ranging from about 0.25 to about 8 mg loss/100,000 revolutions. For example, the Einlechner abrasion index may range from about 0.5 to about 7; alternatively, from about 0.5 to about 5, or alternatively, from about 0.75 to about 4 mg loss/100,000 revolutions. Other suitable ranges for the Einlechner abrasion index will be apparent from the present disclosure.

In one embodiment, the silica spherical particles may have a bulk density after compaction ranging from about 25 to about 65 lb/ft ³ , without being limited to this range. In another embodiment, the bulk density after compaction may be in the range of about 35 to about 60 lb/ft ³ , in a preferred embodiment, from about 40 to about 65 lb/ft ³ , and in a more preferred embodiment, from about 40 to about 60 lb /ft ³ . In yet another embodiment, the bulk density after compaction may be in the range of about 35 to about 65 lb/ft ³ . Other suitable ranges for bulk density after compaction will be apparent from the present disclosure.

The silica particles can typically have an oil absorption ranging from about 30 to about 115 cm ³ /100 g, in a preferred embodiment from about 30 to about 90 cm ³ /100 g, and in a more preferred embodiment from about 30 to about 80 cm ³ /100, Additionally or alternatively, spherical particles of silicon dioxide may have a relatively narrow particle size distribution, when expressed in wt. % residue on a 325 mesh sieve (the amount remaining on a 325 mesh sieve), typically less than or equal to about 1.2 wt. %. In some embodiments, the amount of residue on a 325 mesh sieve may be less than or equal to about 1 wt. %, in the preferred embodiment, less than or equal to about 0.75 wt. %, in the preferred embodiment, less than or equal to about 0.5 wt. % and in a more preferred embodiment less than or equal to 0.3 wt. %. Other suitable ranges for oil absorption and 325 mesh residue will be apparent from the present disclosure.

In these and other embodiments, any spherical silica particles may be amorphous, may be synthetic, or may be both amorphous and synthetic. In addition, in certain embodiments of the present invention, the spherical silica particles may include, but are not limited to, precipitated silica particles.

The spherical silica particles can also be described in terms of their Film Cleaning Index (FPR), which is a measure of the cleaning performance of a dentifrice composition containing silica particles. In one embodiment, the particles of silicon dioxide may differ in the value of the COP at a content of 20 wt. % ranging from about 50 to about 110, in another embodiment from about 70 to about 110, in another embodiment from about 80 to about 110, in another embodiment from about 60 to about 100, and in yet another embodiment implementation from about 70 to about 105. The value of the ratio POP/IRD (at a content of 20 wt.%) in one embodiment, can often be from about 0.5:1 to about 1.3:1, in another embodiment from about 0.5:1 to about 1.2:1, in another embodiment from about 0.5:1 to about 1:1, and in another embodiment from about 0.5:1 to about 0.7: 1.

METHODS FOR OBTAINING SILICON DIOXIDE PARTICLES

The preparation of the spherical silica particles disclosed in the present invention is not limited to the use of any particular synthetic procedure. However, to provide the necessary sphericity, a continuous loop reactor can be used to produce spherical silica and/or silicate particles. This method and the reactor system used therein (which may include a continuous circulation loop of one or more loop reactor tubes) are described in U.S. Nos. 8945517 and 8609068, incorporated herein by reference in their entirety. To improve the sphericity of the particles, the changes described in the present invention are made to the general procedure and reactor system.

Typically, a continuous loop reactor technique comprises (a) continuously feeding the inorganic acid and alkali metal silicate into a loop reaction zone containing a liquid medium stream (water-based) in which at least a portion of the inorganic acid and alkali metal silicate enter into reacting to produce a silica product (eg silica particles) in a liquid medium contained in the loop reaction zone; (b) continuously recirculating the liquid medium through the loop reaction zone; and (c) continuously discharging from the loop reaction zone a portion of the liquid medium containing the silica product. In preferred embodiments of the present invention, steps (a)-(c) are carried out simultaneously.

Typically, although not necessary, the feed positions of the inorganic acid and alkali metal silicate into the loop reaction zone are different, and the total volumetric feed rate of the acid and silicate is proportional to, and often equal to, the discharge rate of the liquid medium containing the silica product. All or substantially all of the content (greater than 95% by weight) of the loop reaction zone is recycled. The liquid medium may, for example, be recirculated through the loop reaction zone at a rate ranging from about 50% rpm (the recirculation rate (per minute) corresponds to half the total volume of liquid medium contained in the loop reaction zone) to about 1000 rpm. %/min (recirculation rate (per minute) corresponds to 10 total volumes of liquid medium contained in the loop reaction zone) or from about 75 to about 500 vol.%/min. Typical and non-limiting ranges for the volumetric rate of liquid medium recirculation through the loop reaction zone in one embodiment include the range from about 15 to about 150 L/min and in another embodiment from about 60 to about 100 L/min.

The loop reaction zone may include a continuous circulation loop of one or more loop reactor tubes. For example, the process can be carried out continuously in a single loop reactor. Any suitable pump may be used to recirculate the liquid medium through the loop reaction zone. The temperature of the liquid medium in the loop reaction zone can be controlled using any suitable technique or control system.

In one embodiment, the alkali metal silicate may include sodium silicate and the inorganic acid may include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or a combination thereof. In another embodiment, the alkali metal silicate may include sodium silicate and the inorganic acid may include an acidic solution of aluminum sulfate. In these and other embodiments, the resulting silica product may include precipitated silica or precipitated sodium aluminosilicate. The pH of the liquid medium that is recycled through the loop reaction zone can range from about 2.5 to about 10, but is more commonly in the range from about 6 to about 10, in the preferred embodiment from about 6.5 to about 8, 5, and in a more preferred embodiment, from about 7 to about 8.

To provide improved sphericity, the continuous loop reactor process for producing the silica product can be run under low shear or no shear conditions. Thus, for example, the stator sieve located in the agitator of the loop reactor can be removed to ensure low or no shear operation. Alternatively, a stator screen with large holes (e.g., slots, round holes, square holes, etc.) can be used to provide low or no shear operation so that the stator screen located in the looped reaction zone has holes having a cross-sectional area equal to more than 3 mm ² (for example, a cross-sectional area in one embodiment equal to more than 10 mm ² in another embodiment equal to more than 50 mm ² in another embodiment equal to more than 100 mm ² in another embodiment implementation equal to more than 500 mm ² , etc.). In addition, to reduce shear in the loop reaction zone, the mixing rpm of the mixer can be reduced to less than 3000 rpm, in the preferred embodiment, to less than 2500 rpm, and in the more preferred embodiment, to less than 2000 rpm. rpm In addition, the recycling step of the process, step (b), can be carried out at a relatively high temperature, often in the range of about 85 to about 100°C, in another embodiment, from about 90 to about 100°C, and in yet another embodiment from about 88 to about 98°C. Additionally or alternatively, to provide low or no shear operation, the shear frequency in the loop reaction zone may be less than 1,000,000 interactions/min in one embodiment, less than 750,000 interactions/min in another embodiment, less than 500,000 in another embodiment. interactions/min, and in yet another embodiment, less than 250,000 interactions/min. The shear frequency is defined as the number of interactions between the flow from the rotor to the stator: RPM×N _R ×N _S , where RPM denotes the number of revolutions per minute of the mixer/rotor, N _R denotes the number of rotor blades/teeth, and N _S denotes the number holes / slots (holes) of the stator. Thus, using a 4-bladed rotor with 10 large round stator holes and a speed of 2700 rpm means 108,000 interactions/min (small shear), while using a 400 small stator holes means 4,320,000 interactions/min (large shear). shear force).

To ensure applicability in the final dentifrice and in other cases, after the silica particles are discharged from the loop reaction zone, their pH value can often be adjusted to be in the range of from about 5 to about 8.5, and in some cases in the preferred embodiment from about 5.5 to about 8 object, and in a more preferred embodiment, from about 5.5 to about 7.5, without being limited to these ranges.

The methods disclosed herein may optionally further include, following the pH adjustment step, a filtration step to isolate the silica particles, a washing step to wash the silica particles, a drying step (e.g., spray drying) to dry the silica particles, or any combination of steps. filtering, washing and drying, and they are carried out in any suitable order.

DENTAL CARE COMPOSITIONS

The spherical silica particles can be used in any suitable composition and for any suitable end use. Silica particles can often be used in oral care compositions such as a dentifrice composition. The dentifrice composition may contain any suitable amount of silica particles, such as from about 0.5 to about 50 wt. %, in the preferred embodiment, from about 1 to about 50 wt. %, in a more preferred embodiment, from about 5 to about 35 wt. %, in a more preferred embodiment, from about 10 to about 40 wt. % and in a more preferred embodiment, from about 10 to about 30 wt. % spherical silica particles. These expressed in wt. The % amounts are based on the total weight of the dentifrice composition.

The dentifrice composition may be in any suitable form, such as a liquid, powder, or paste. In addition to silica particles, the dentifrice composition may contain other ingredients or additives, non-limiting examples of which include a humectant, solvent, binder, therapeutic agent, chelating agent, thickener other than silica particles, surfactant, abrasive. , other than particles of silicon dioxide, sweetener, coloring agent, flavoring agent, preservative, etc., as well as any combination thereof.

Moisture-retaining agents are intended to impart a consistency or "mouth-friendly texture" to the dentifrice and to prevent the dentifrice from drying out. Suitable humectants include polyethylene glycol (of various molecular weights), propylene glycol, glycerol, erythritol, xylitol, sorbitol, mannitol, lactitol, and hydrogenated starch hydrolysates, and mixtures thereof. In some compositions, humectants are contained in an amount of from about 20 to about 50 wt. % based on the weight of the dentifrice composition.

The solvent may be present in the dentifrice composition in any suitable amount, and the solvent will typically include water. If water is used, it is preferably if it is deionized and free of impurities, and it can be contained in the dentifrice in an amount ranging from 5 to about 70 wt. % and in another embodiment, from about 5 to about 35 wt. % based on the weight of the dentifrice composition.

Therapeutic agents may also be used in the compositions of the present invention, for example to provide prevention or treatment of dental caries, periodontal disease and temperature sensitivity. Suitable therapeutic agents may include, but are not limited to, fluoride sources such as sodium fluoride, sodium monofluorophosphate, potassium monofluorophosphate, tin(II) fluoride, potassium fluoride, sodium fluorosilicate, ammonium fluorosilicate, and the like; condensed phosphates such as tetrasodium pyrophosphate, tetrapotassium pyrophosphate, disodium dihydrogen pyrophosphate, trisodium monohydrogen pyrophosphate; tripolyphosphates, hexametaphosphates, trimetaphosphates and pyrophosphates; antimicrobials such as triclosan, biguanidines such as alexidine, chlorhexidine and chlorhexidine gluconate; enzymes such as papain, bromelain, glucoamylase, amylase, dextranase, mutanase, lipases, pectinase, tannase and proteases; quaternary ammonium compounds such as benzalkonium chloride (BZK), benzethonium chloride (BZT), cetylpyridinium chloride (CPC) and domiphene bromide; metal salts such as zinc citrate, zinc chloride and tin(II) fluoride; sanguinaria extract and sanguinarine; essential oils such as eucalyptol, menthol, thymol and methyl salicylate; aminofluorides; peroxides, etc. The therapeutic agents may be used alone or in combination in dentifrice compositions and in any therapeutically safe and effective amount or dose.

Thickening agents are useful in dentifrice compositions to provide a gel-like structure, the presence of which stabilizes the toothpaste and prevents phase separation. Suitable thickening agents include silica thickener; starch; a mixture of starch and glycerin; gums such as karaya gum (sterculia gum), tragacanth gum, gum arabic, ghatti gum, acacia gum, xanthan gum, guar gum and cellulose gum; magnesium aluminum silicate (veegum); carrageenan; sodium alginate; agar-agar; pectin; gelatin; cellulose compounds such as cellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxymethylcellulose, hydroxymethylcarboxypropylcellulose, methylcellulose, ethylcellulose and sulfate cellulose; natural and synthetic clays such as hectorite clays; and their mixtures. Typical contents of thickening agents or binders are up to about 15 wt. % based on the weight of the toothpaste or dentifrice composition.

Silica thickeners suitable for use in a toothpaste formulation include, for example, amorphous precipitated silica such as ZEODENT 165 silica. 177 and/or 265, all manufactured by J.M. Huber Corporation.

Surfactants can be used in the dentifrice compositions of the present invention to provide compositions that are more cosmetically acceptable. Preferably, the surfactant is a detergent which imparts detergent and foaming power to the composition. Suitable surfactants are anionic, cationic, nonionic, zwitterionic, amphoteric, and betaine surfactants used in safe and effective amounts, such as sodium lauryl sulfate, sodium dodecylbenzenesulfonate, lauroyl sarcosinates, myristoyl sarcosinates, palmitoyl sarcosinates, stearoyl sarcosinates, and oleoyl sarcosine. are you alkali metal or ammonium, polyoxyethylene sorbitan monostearate, isostearate and laurate, sodium lauryl sulfoacetate, N-lauroylsarcosine, salts of N-lauroyl, N-myristoyl or N-palmitoylsarcosine with sodium, potassium and ethanolamine, condensation products of polyethylene oxide and alkylphenols, cocoamidopropyl betaine, lauramidopropyl betaine, palmityl betaine, etc. The preferred surfactant is sodium lauryl sulfate. Surfactant is usually contained in the compositions proposed in the present invention, in an amount of from about 0.1 to about 15 wt. %, in the preferred embodiment, from about 0.3 to about 5 wt. % and in a more preferred embodiment, from about 0.3 to about 2.5 wt. %).

The silica particles of the present invention may be used in a dentifrice composition alone as an abrasive, or as an additive or co-abrasive with other abrasives as described herein or known in the art. Thus, the dentifrice compositions of the present invention may contain any amount of conventional types of abrasive additives. Other such abrasive particles include, for example, precipitated calcium carbonate (PCC), ground calcium carbonate (PCC), chalk, bentonite, dicalcium phosphate or dihydrates thereof, silica gel (by itself and having any structure), precipitated silica, amorphous precipitated silica. (by itself or any structure), perlite, titanium dioxide, dicalcium phosphate, calcium pyrophosphate, alumina, hydrated alumina, calcined alumina, aluminum silicate, insoluble sodium metaphosphate, insoluble potassium metaphosphate, insoluble magnesium carbonate, zirconium silicate , crushed thermosetting resins and other suitable abrasive materials. Such materials can be included in dentifrice compositions to control the polishing characteristics of the target composition.

Sweeteners can be added to the dentifrice composition (eg, toothpaste) to impart a pleasant taste to the product. Suitable sweeteners include saccharin (as the sodium, potassium, or calcium salt of saccharin), cyclamate (as the sodium, potassium, or calcium salt), acesulfame-K, thaumatin, neohesperidine dihydrochalcone, ammoniated glycyrrhizin, dextrose, levulose, sucrose, mannose, and glucose.

Dyes can be added to improve the aesthetic appeal of the product. Suitable colorants include, but are not limited to, those approved by the relevant regulatory authorities such as the FDA (Food and Drug Administration) and listed in the European Food and Drug Guidelines, and these include pigments, such as TiO2, and dyes such as FD&C (Federal Food, Drug, and Cosmetic Act) and D&C (Drug and Cosmetic Act) dyes.

Flavoring agents can also be added to dentifrice compositions. Suitable flavoring agents include, but are not limited to, wintergreen oil, peppermint oil, peppermint oil, sassafras oil and clove oil, cinnamon, anethole, menthol, thymol, eugenol, eucalyptol, lemon, orange and other similar food flavorings intended for imparting fruity notes, spicy notes, etc. These flavoring agents typically contain a mixture of aldehydes, ketones, esters, phenols, acids, and aliphatic, aromatic, and other alcohols.

Preservatives can also be added to the compositions of the present invention to prevent bacterial growth. Suitable preservatives approved for use in oral compositions, such as methyl paraben, propyl paraben, and sodium benzoate, may be added in safe and effective amounts.

Other ingredients may be used in the dentifrice composition such as desensitizing agents, healing agents, other anti-caries agents, chelating/binding agents, vitamins, amino acids, proteins, other anti-plaque/calculus agents, opacifiers, antibiotics, antienzymes, enzymes, pH adjusting agents, oxidizing agents, antioxidants, and the like.

EXAMPLES

The present invention is further illustrated by the following examples, which should not be considered as limiting the scope of the present invention in any way. After reading the description given in the present invention, a person with general training in the art can independently propose various other embodiments, modifications and equivalents without deviating from the essence of the present invention or the scope of the appended claims.

The multipoint BET surface values disclosed in the present invention were determined using a Micromeritics TriStar II 3020 VI.03 instrument using the nitrogen adsorption BET method described in Brunaur et al., J. Am. Chem. Soc, 60, 309 (1938).

The surface areas of CTAB (determined by the adsorption of CTAB (cetyltrimethylammonium bromide)) disclosed in the present invention were determined by the adsorption of CTAB on the surface of the silica material, the excess was separated by centrifugation, and the amount was determined by titration with sodium lauryl sulfate using a surfactant-selective electrode. More precisely, about 0.5 g of silica particles were placed in a 250 ml beaker containing 100 ml of CTAB solution (5.5 g/l), stirred for 1 hour on an electric hot plate with a stirrer, then centrifuged for 30 minutes at a speed equal to 10,000 rpm. In a beaker with a volume of 100 ml, 1 ml of a 10% solution of Triton X-100 was added to 5 ml of a clear supernatant. The pH value was adjusted to 3-3.5 with 0.1N. HCl solution and the sample was titrated with 0.01 M sodium lauryl sulfate solution using a surfactant selective electrode (Brinkmann SUR1501-DL) to determine the limit value.

Median particle size (d50) means a particle size such that 50% of the sample particles are smaller and 50% of the sample particles are larger. Median particle size (d50), average particle size (average), d90 and d10 were determined by laser diffraction using a Horiba LA 300 instrument. For analysis, dry particles were placed in the instrument and the samples were deagglomerated using ultrasonic vibration for 2 min.

To determine bulk density and bulk density after compaction, 20 g of the sample was placed in a 250 ml measuring cylinder with a flat rubber bottom. The initial volume was recorded and used to calculate the bulk density by dividing it by the weight of the sample used. The cylinder was then placed in a tapping density machine where it was rotated in an eccentric at a speed of 60 rpm. The eccentric is designed so that it lifts a distance equal to 5.715 cm and resets the cylinder once per second until the sample volume becomes constant, usually within 15 minutes. This final volume is recorded and used to calculate the bulk density after compaction by dividing it by the weight of the sample used.

The Einlechner Abrasion Index is a measure of the hardness/abrasiveness of silica particles and is detailed in U.S. Pat. No. 6,616,916, incorporated herein by reference, and its definition includes the use of an Einlechner AT-1000 abrasion tester, which is typically used as follows: (1) a long brass wire mesh is weighed and exposed to a 10% aqueous silica slurry within a fixed period of time; then (2) determine the amount of abraded material as (mg of brass abraded from a long wire mesh)/100,000 revolutions (mg loss/100,000 revolutions).

Oil absorption values were determined by the trituration method described in ASTM D281 using linseed oil (cm ³ of oil adsorbed per 100 g of particles). Generally, a higher oil absorption indicates a particle having a higher proportion of large pores, also described as being more structured.

Water absorption values were determined using a rotary rheometer with an absorption meter "C" manufactured by C.W. Brabender Instruments Inc. Approximately 1/3 cup of the silica sample was placed in the kneading chamber of the absorbance meter and mixed at a speed of 150 rpm. Water was then added at a rate of 6 ml/min and the torque needed to stir the powder was recorded. Since water is absorbed by the powder, the maximum torque is reached when the free-flowing powder turns into a paste. Then, the total volume of water added to provide the maximum torque value was normalized to the amount of water that can be absorbed with 100 g of the powder. Since the powder was used as received (not previously dried), the amount of free moisture contained in the powder was used to calculate the "AbC water absorption value corrected for the amount of moisture" using the equation below.

An absorbance meter is typically used to determine the oil absorption of soot according to ASTM D 2414, Methods B and C, and ASTM 3493.

The pH values disclosed in the present invention (pH 5% solution) were determined in an aqueous system containing 5 wt. % solids in deionized water, using a pH meter.

The amount of residual silica sample on a 325 sieve (wt %) was determined using a standard 44 µm or 0.0017 inch US #325 sieve (stainless steel wire mesh) by weighing 10.0 g of the sample to an accuracy of to 0.1 g in a 1 quart Hamilton mixer cup (Model #30), adding 170 ml of distilled or deionized water, and stirring the suspension for at least 7 minutes. The mixture was transferred to a 325 mesh sieve and water was sprayed directly onto the sieve at a pressure of 20 lbf/in ² i.d. for 2 minutes, while the spray head was kept at a distance from the sieve of about 4 to 6 inches . Then the resulting residue was transferred to a watch glass, dried in an oven at 150°C for 15 min, then cooled and weighed on an analytical balance.

The cleaning performance of the silica materials contained in a dentifrice composition is typically quantified by a Film Cleaning Index ("FRP"). The ROP technique examines the ability of a dentifrice composition to remove a thin film from a tooth under specified brushing conditions. The method for determining POP is described in the publication "In Vitro Removal of Stain With Dentifrice" G.K. Stookey, et al., J. Dental Res., 61, 1236-9, 1982, the content of which regarding POP is incorporated into the present invention by reference. The COP values are dimensionless.

The degree of radioactive dentine abrasion (RDA) of the dentifrice compositions of the present invention was determined by the method described in Hefferen, Journal of Dental Res., July-August 1976, 55 (4), pp. 563-573 and described by Wason in U.S. Nos. 4340583, 4420312 and 4421527, the content of all these publications relating to the definition of IRD, are incorporated into the present invention by reference. The IRD values are dimensionless.

EXAMPLES 1A-2A

Irregularly shaped silica particles

Table I lists some characteristics of the comparative silica materials 1A and 2A, which have an irregular and non-spherical particle morphology. In FIG. 1 (Example 1A) and FIG. 2 (Example 2A) shows SEM images showing the irregular and non-spherical shape of the particles of Examples 1A and 2A. Examples 1A and 2A are conventional silica materials available from Huber Engineered Materials.

EXAMPLES 3A-8A

Spherical silica particles

Particles of examples 3A-8A were prepared using a continuous loop reactor technique (see, for example, U.S. Patent Nos. 8,945,517 and 8,609,068) and produced silica particles having a spherical morphology and a narrower particle size distribution (e.g., less residue of the final silica product on a 325 mesh sieve).

In FIG. 3 shows an apparatus including a continuous loop reactor in which the recirculation loop is configured such that the reaction slurry is circulated many times before being discharged. The circuit consisted of sections of rigid tubing connected together with sections of flexible hose. The inner diameter of the tube/hose was approximately 1 inch. A pump was installed on one side of the circuit to circulate the reaction slurry and an inline Silverson mixer was installed on the opposite side to provide additional shear force in the system, as well as to load the acid component. A static mixer-heat exchanger was installed between the pumps to provide a means of controlling the temperature during the preparation of the silica material. An outlet pipe was added located after the acid addition position, with which the product obtained at different addition rates of silicate and acid can be discharged. The outlet pipe was also provided with a back pressure control valve to allow operation of the system at temperatures in excess of 100°C. A product discharge outlet was installed to collect the product in a tank for further modification (eg pH adjustment) or the product was discharged directly into a rotary filter or filter press. An acid may optionally be added to the product discharge outlet to avoid pH adjustment if the silica product is produced at a pH greater than 7.0.

For some example particles, the Silverson inline mixer was modified to provide a high degree of agitation without shear. This was done by removing the stator screen from the Silverson mixer and operating the apparatus using only the support frame and conventional mixer head. Thus, the particle size can be controlled by changing the rotation speed and the recirculation speed in the Silverson mixer (for example, reducing both speeds can increase the average particle size).

For the particles of Examples 3A-8A, the precipitated silica, sodium sulfate, sodium silicate and water were added before adding the acid and silicate to the system and recirculated at a rate of 80 l/min. This step was performed to fill the recirculation loop with the appropriate contents at typical batch concentrations to minimize purge time before collecting the desired product.

To obtain particles of example 3A, 1.5 kg of particles of example 1A, 1.34 kg of sodium sulfate, 11.1 l of sodium silicate (MO (mass ratio) = 3.32, 19.5%) and 20 l of water were added to the recirculation loop. , then heated to 95°C at a recirculation rate of 80 l/min, running the Silverson mixer at 60 Hz (3485 rpm) and using a conventional rotor/stator configuration. Sodium silicate (MO = 3.32, 20.0%) and sulfuric acid (17.1%) were simultaneously added to the circuit at a silicate addition rate of 1.7 l/min and at an acid addition rate sufficient to maintain the value pH equal to 7.5. If necessary, to maintain the desired pH, the acid addition rate was adjusted accordingly. Acid and silicate were added under these conditions over a period of 40 minutes to remove unwanted silica from the system, then the desired material was collected. After 40 minutes, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 rpm while maintaining the temperature at about 80°C. After collecting the required amount of product, the addition of acid and silicate was stopped and the contents of the loop were allowed to circulate around the loop. The silica product in the collection vessel was adjusted to pH 6.0 by manual addition of sulfuric acid and then filtered and washed until a conductivity of ~1500 μS was obtained. The slurry was then re-adjusted to pH 6.0 with sulfuric acid and spray dried.

To obtain particles of example 4A, 1.5 kg of particles of example 1A, 1.34 kg of sodium sulfate, 11.1 l of sodium silicate (MO = 2.65, 20.0%) and 20 l of water were added to the recirculation loop, then heated to 95° C. at a recirculation rate of 80 l/min with the Silverson mixer running at 60 Hz (3485 rpm) and without the use of a stator screen. Sodium silicate (MO = 2.65, 20.0%) and sulfuric acid (17.1%) were simultaneously added to the loop at a silicate addition rate of 1.7 l/min and at an acid addition rate sufficient to maintain pH value equal to 7.5. If necessary, to maintain the desired pH, the acid addition rate was adjusted accordingly. Acid and silicate were added under these conditions over a period of 40 minutes to remove unwanted silica from the system, then the desired material was collected. After 40 minutes, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 rpm while maintaining the temperature at about 80°C. After collecting the required amount of product, the addition of acid and silicate was stopped and the contents of the loop were allowed to circulate around the loop. The silica product in the collection vessel was adjusted to pH 6.0 by manual addition of sulfuric acid and then filtered and washed until a conductivity of ~1500 μS was obtained. The slurry was then re-adjusted to pH 6.0 with sulfuric acid and spray dried.

To obtain particles of example 5A, 1.5 kg of particles of example 1A, 1.34 kg of sodium sulfate, 11.1 l of sodium silicate (MO = 2.65, 26.6%) and 20 l of water were added to the recirculation loop, then heated to 95° C. at a recirculation rate of 80 l/min with the Silverson mixer running at 60 Hz (3485 rpm) and without the use of a stator screen. Sodium silicate (MO = 2.65, 26.6%) and sulfuric acid (22.8%) were simultaneously added to the circuit at a silicate addition rate of 1.7 l/min and at an acid addition rate sufficient to maintain pH value equal to 7.5. If necessary, to maintain the desired pH, the acid addition rate was adjusted accordingly. Acid and silicate were added under these conditions over a period of 40 minutes to remove unwanted silica from the system, then the desired material was collected. After 40 minutes, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 rpm while maintaining the temperature at about 80°C. After collecting the required amount of product, the addition of acid and silicate was stopped and the contents of the loop were allowed to circulate around the loop. The silica product in the collection vessel was adjusted to pH 6.0 by manual addition of sulfuric acid and then filtered and washed until a conductivity of ~1500 μS was obtained. The slurry was then re-adjusted to pH 6.0 with sulfuric acid and spray dried.

To obtain particles of example 6A, 1.5 kg of particles of example 1A, 1.34 kg of sodium sulfate, 11.1 l of sodium silicate (MO = 2.65, 26.6%) and 20 l of water were added to the recirculation loop, then heated to 95° C. at a recirculation rate of 80 l/min with the Silverson mixer running at 15 Hz (871 rpm) and without the use of a stator screen. Sodium silicate (MO = 2.65, 26.6%) and sulfuric acid (22.8%) were simultaneously added to the circuit at a silicate addition rate of 1.7 l/min and at an acid addition rate sufficient to maintain pH value equal to 7.5. If necessary, to maintain the desired pH, the acid addition rate was adjusted accordingly. Acid and silicate were added under these conditions over a period of 40 minutes to remove unwanted silica from the system, then the desired material was collected. After 40 minutes, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 rpm while maintaining the temperature at about 80°C. After collecting the required amount of product, the addition of acid and silicate was stopped and the contents of the loop were allowed to circulate around the loop. The silica product in the collection vessel was adjusted to pH 6.0 by manual addition of sulfuric acid and then filtered and washed until a conductivity of ~1500 μS was achieved. The slurry was then re-adjusted to pH 6.0 with sulfuric acid and spray dried.

To obtain particles of example 7A, 1.5 kg of particles of example 1A, 1.34 kg of sodium sulfate, 11.1 l of sodium silicate (MO = 2.65, 26.6%) and 20 l of water were added to the recirculation loop, then heated to 95° C. at a recirculation rate of 80 l/min with the Silverson mixer running at 30 Hz (1743 rpm) and without the use of a stator screen. Sodium silicate (MO = 2.65, 26.6%) and sulfuric acid (22.8%) were simultaneously added to the circuit at a silicate addition rate of 1.7 l/min and at an acid addition rate sufficient to maintain pH value equal to 7.5. If necessary, to maintain the desired pH, the acid addition rate was adjusted accordingly. Acid and silicate were added under these conditions over a period of 40 minutes to remove unwanted silica from the system, then the desired material was collected. After 40 minutes, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 rpm while maintaining the temperature at about 80°C. After collecting the required amount of product, the addition of acid and silicate was stopped and the contents of the loop were allowed to circulate around the loop. The silica product in the collection vessel was adjusted to pH 6.0 by manual addition of sulfuric acid and then filtered and washed until a conductivity of ~1500 μS was achieved. The slurry was then re-adjusted to pH 6.0 with sulfuric acid and spray dried.

To obtain particles of example 8A, 1.5 kg of particles of example 1A, 1.34 kg of sodium sulfate, 11.1 l of sodium silicate (MO = 3.32, 32.3%) and 20 l of water were added to the recirculation loop, then heated to 90° C. at a recirculation rate of 80 l/min with the Silverson mixer running at 30 Hz (1742 rpm) and without the use of a stator screen. Sodium silicate (MO = 3.32, 32.2%) and sulfuric acid (22.8%) were simultaneously added to the circuit at a silicate addition rate of 1.7 l/min and at an acid addition rate sufficient to maintain pH value equal to 7.5. If necessary, to maintain the desired pH, the acid addition rate was adjusted accordingly. Acid and silicate were added under these conditions over a period of 40 minutes to remove unwanted silica from the system, then the desired material was collected. After 40 minutes, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 rpm while maintaining the temperature at about 80°C. The silica product in the collection vessel was adjusted to pH 6.0 by manual addition of sulfuric acid and then filtered and washed until a conductivity of ~1500 μS was achieved. The slurry was then re-adjusted to pH 6.0 with sulfuric acid and spray dried.

Table I compares some characteristics of the particles of silica obtained in examples 3A-8A, with the corresponding characteristics of the particles of comparative examples 1A-2A. The particles of Examples 3A-8A have a median particle size (d50) in a wide range of about 3 to 21 microns, but a narrow particle size distribution. Examination of the SEM images also showed the presence of a narrow particle size distribution and spherical particle morphology. Representative SEM images for the particles of Examples 3A-8A are shown in FIGS. 4-9, respectively. The corresponding sphericity coefficient (S ₈₀ ) for the particles of all examples 3A-8A was greater than 0.9.

EXAMPLES 1B-8B

EXAMPLES 3C and 7C

Toothpaste Compositions and Determination of POP and RDI Values

Silica samples of examples 1A-8A were used in toothpaste compositions 1B-8B at a content of the corresponding silica of 20 wt. %, and in toothpaste compositions 3C and 7C at the content of the corresponding silicon dioxide, which is 10 wt. % as shown in Table II.

To investigate the effect of silica characteristics on POP and RDI performance, POP and RDI values were determined (at Indiana University School of Dentistry) using toothpaste formulations. Table III presents the values of POP and RDI for compositions of toothpaste. Surprisingly, it has been found that as the size of the highly spherical silica particles increases, the IRD value decreases significantly and the SPD value also decreases, but to a lesser extent. These results are unexpected and different from those typically obtained using conventional precipitated silica materials (which are irregularly shaped and not spherical). Without being limited by theoretical considerations, it can be assumed that, since the determination of the IRF value is carried out on an inhomogeneous surface consisting of dentin and hollow dentinal tubules, which have a size of about 2-3 μm, spherical silica particles partially enter the tubules and then are embedded in the opposite wall when they are pushed out of the tubules with a toothbrush as they move along the surface of the dentin.

EXAMPLES 9A-13A

Irregularly shaped silica particles

Table IV lists some characteristics of the comparative silica materials 9A-13A, which have irregular and non-spherical particle morphology. The material of Example 9A is a conventional silica material available from Huber Engineered Materials and the materials of Examples 10A-13A were obtained by air milling the unmilled material of Example 9A to achieve a particle size d50 of 3.5 µm (Example 10A), 6.2 µm (example 11A), 9.4 µm (example 12A, wide particle size distribution) and 9.3 µm (example 13A, narrow particle size distribution).

EXAMPLES 9V-13V

Toothpaste Compositions and Determination of FAR and RDI The silica samples of Examples 9A-13A were used in Toothpaste Compositions 9B-13B at the respective silica content of 20% by weight. % as shown in Table V.

To investigate the effect of silica characteristics on POP and RDI performance, POP and RDI values were determined (at Indiana University School of Dentistry) using toothpaste formulations. Table VI presents the values of ROP and RDI for compositions of toothpaste. As can be seen from Table VI, increasing the particle size of silica from 3.5 to 9.5 µm does not change the values of IRD or LOI. Thus, in the case of irregularly shaped and non-spherical silica particles, there is no relationship between the particle size and the IWP value, and there is no relationship between the particle size and the FOD value.

DISCUSSION OF THE RESULTS OBTAINED IN THE EXAMPLES

From a comparison of the results in Table III with those in Table VI, it can be concluded that the performance of spherical silica materials is fundamentally (and unexpectedly) different from that of conventional silicas used in dentifrices, which are non-spherical and have an irregular shape. form. In the case of highly spherical materials, the particle size and particle size distribution can be used to control the values of IRD and LOA, while in the case of conventional irregularly shaped silicas, the particle size and particle size distribution do not have a significant effect.

Without being limited by the theoretical considerations below, it can be assumed that the spherical particles are first introduced into the substrate, before they begin to roll on the surface (at first, a high degree of abrasion is observed, but after the particles begin to roll, abrasion practically stops), while a conventional non-spherical and irregularly shaped product will scratch the substrate during the entire time it travels across the substrate.

As shown in Table III, the MDI values obtained for spherical products having small particle sizes (less than 4 µm) are over 200. It is assumed that, since the dentin surface is mostly inhomogeneous, containing both porous material and an organic component, spherical particles partially fall into the tubules and grind the opposite side when leaving it. In the case of highly spherical particles, as the particle size increases, the depth to which they can penetrate into the tubule decreases. It is assumed that this decrease in the depth of penetration into the tubule (and increase in particle size) is the main factor leading to a decrease in the value of IRD. The model for a spherical particle (having a small size) interacting with the dentinal tubule is presented in Fig. 10.

A simple analogy would be a car wheel driving over a pothole. If the pothole is relatively large for a car wheel, then a strong impact is felt when the car drives over the pothole. As the size of the pothole decreases, the intensity of the perceived impact decreases until the pothole is small enough that the car wheel does not sink very deep into the pothole. If the pothole has a given size, then the same effect can be observed by increasing the size of the car wheel. Similarly, in FIG. 11 shows a model for spherical particles of increasing size (4 µm, 5 µm, 6 µm, 10 µm) interacting with a dentinal tubule of about 2.5 µm. As the particle size increases, the depth of particle penetration into the tubules decreases.

Using geometric formulas, based on the diameter of a spherical particle, the penetration depth can be calculated, as described in J.M. Fildes et al., Wear 274-275 (2012) 414-422, incorporated herein by reference in its entirety. Based on the size of the silica particles and the dentinal tubule with a depth of 2.5 μm, corresponding to the IRD value, it is possible to construct a dependence of the penetration depth on the diameter of the particle if it has a spherical shape (see Fig. 12). As the particle size increases from 3.5 µm to 12 µm, the penetration depth of highly spherical particles decreases by about 80%.

The force required for a circular wheel (similar to a spherical particle) to pass over steps of different heights (similar to penetration depth) can also be calculated using the formulas given in "Physics for Scientists and Engineers" Eighth Edition (2010) ; Serway | Jewett, incorporated herein by reference in its entirety. Based on the assumption that the spherical particle, when passing through the tubule, comes into contact with only one side of the tubule (except when it is at the bottom, in which case the contact position is a step), it is possible to approximately calculate the force required to roll out the particle from the tubule. Since the content of particles in dentifrice compositions is by weight and the number of small particles exceeds the number of large particles, it is assumed that the force expressed in Newtons must be converted to mass (in terms of grams). In FIG. 13 shows the dependence of the force required to roll out a 1 g spherical particle from a 2.5 μm tubule on the particle size. As the particle size increases from 6 µm to 12 µm, the force decreases by more than 50%.

In general, it should be noted that from the above drawings, tables and discussion, it can be seen that the characteristics of spherical silica materials are fundamentally (and unexpectedly) different from those of conventional silicas used in dentifrices, which are non-spherical and have an irregular shape, this is features refers to their IRD characteristics. In the case of highly spherical materials, the particle size is the main factor for controlling the values of IRD and FOP, in contrast to conventional irregularly shaped silicas, in which the particle size does not have a significant effect.

The present invention has been described above with reference to numerous embodiments and specific examples. Many changes will be suggested by those skilled in the art in light of the above detailed description. All such obvious changes are within the full intended scope of the appended claims. Other embodiments of the present invention may include, but are not limited to, the following (embodiments are described using the expression "comprising", but alternatively, the expressions "consisting mainly of" or "consisting of") can be used:

Embodiment 1. Silica particles characterized by:

(i) a median particle size d50 greater than or equal to about 6 microns;

(ii) a ratio (d90-d10)/d50 ranging from about 1.1 to about 2.4;

(iii) the value of IRD at a content of 20 wt. % ranging from about 40 to about 200; And

(iv) a sphericity coefficient (S ₈₀ ) greater than or equal to about 0.9.

Embodiment 2 The silica particles of Embodiment 1 wherein the median particle size d50 is in the range of about 7 to about 25 microns.

Embodiment 3 The silica particles of Embodiment 1 wherein the median particle size d50 is in the range of about 8 to about 20 microns.

Embodiment 4. Silica particles according to any one of Embodiments 1-3, wherein the ratio (d90-d10)/d50 is in the range of about 1.1 to about 2.2.

Embodiment 5. Silica particles according to any one of Embodiments 1-3, wherein the ratio (d90-d10)/d50 is in the range of about 1.2 to about 2.

Option implementation 6. Particles of silicon dioxide, corresponding to any of the embodiments 1-5, where the value of the IRD at a content of 20 wt. %, is in the range from about 50 to about 190.

Option implementation 7. Particles of silicon dioxide, corresponding to any of the embodiments 1-5, where the value of the IRD at a content of 20 wt. %, ranges from about 85 to about 180.

Embodiment 8 The silica particles of any one of Embodiments 1-7, wherein the silica particles are further characterized by an oil absorption ranging from about 30 to about 115 ^cc /100 g.

Embodiment 9 The silica particles of any one of Embodiments 1-7, wherein the silica particles are further characterized by an oil absorption ranging from about 30 to about 90 ^cc /100 g.

Embodiment 10. The silica particles of any one of Embodiments 1-9, wherein the silica particles further have a bulk density after compaction ranging from about 25 to about 65 lb/ft ³ .

Embodiment 11. The silica particles of any one of Embodiments 1-9, wherein the silica particles further have a bulk density after compaction ranging from about 40 to about 60 lb/ft ³ .

Embodiment 12 The silica particles of any one of Embodiments 1-11, wherein the silica particles are further characterized by a BET surface area ranging from about 10 to about 200 m ² /g.

Embodiment 13 The silica particles of any one of Embodiments 1-11, wherein the silica particles are further characterized by a BET surface area ranging from about 20 to about 100 m ² /g.

Embodiment 14. The silica particles of any one of Embodiments 1-13, wherein the silica particles are further characterized by a 325 mesh residue of less than or equal to about 1.2 wt. %.

Embodiment 15. The silica particles of any one of Embodiments 1-13, wherein the silica particles are further characterized by a 325 mesh residue of less than or equal to about 0.5 wt. %.

Embodiment 16 The silica particles of any one of Embodiments 1-15 wherein the sphericity coefficient (S ₈₀ ) is greater than or equal to about 0.92.

Embodiment 17 The silica particles of any one of Embodiments 1-15 wherein the sphericity coefficient (S ₈₀ ) is greater than or equal to about 0.94.

Embodiment 18. The silica particles of any one of Embodiments 1-17, wherein the silica particles are further characterized by an Einlechner abrasion value ranging from about 0.5 to about 7 mg loss/100,000 revolutions.

Embodiment 19 The silica particles according to any one of Embodiments 1-18, wherein the silica particles are precipitated silica particles.

Embodiment 20 The silica particles according to any one of Embodiments 1-19 wherein the silica particles are amorphous.

Embodiment 21 A composition comprising silica particles according to any one of Embodiments 1-20.

Embodiment 22 A dentifrice composition comprising silica particles according to any one of Embodiments 1-20.

Embodiment 23. Composition for caring for teeth, containing from about 0.5 to about 50 wt. % silica particles corresponding to any of embodiments 1-20.

Embodiment 24. Composition for caring for teeth, containing from about 5 to about 35 wt. % silica particles corresponding to any of embodiments 1-20.

Embodiment 25. A dentifrice composition according to any one of embodiments 22-24, wherein the composition further comprises at least one of the following: a humectant, a solvent, a binder, a therapeutic agent, a chelating agent, a thickener other than silica particles , a surfactant, an abrasive other than silica particles, a sweetener, a coloring agent, a flavoring agent and a preservative, or any combination thereof.

Embodiment 26. Method for producing silica particles, the method includes:

(a) continuously feeding inorganic acid and alkali metal silicate into a loop reaction zone containing a liquid medium stream in which at least a portion of the inorganic acid and alkali metal silicate react to form silica particles in the liquid medium contained in the loop reaction zone ;

(b) continuous recirculation of the liquid medium through the loop reaction zone, where the loop reaction zone does not include a stator screen or the loop reaction zone includes a stator screen with holes having a cross-sectional area equal to more than 3 mm ² or the shear frequency in the loop reaction zone is less than 1000000 interactions / min, or both; And

(c) continuously discharging from the loop reaction zone a portion of the liquid medium containing silica particles.

Embodiment 27. The method according to Embodiment 26, wherein steps (a) to (c) are carried out simultaneously.

Embodiment 28. The method according to Embodiment 26 or 27 wherein the loop reaction zone includes a continuous circulation loop of one or more loop reactor tubes.

Embodiment 29. A method according to any one of Embodiments 26-28, wherein:

inorganic acid and alkali metal silicate are loaded into the loop reaction zone at different positions of the loop reaction zone;

the inorganic acid includes sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or a combination thereof, and the alkali metal silicate includes sodium silicate.

Embodiment 30. The method of any one of Embodiments 26-29 wherein the liquid medium is recycled through the loop reaction zone at a pH ranging from about 6 to about 10.

Embodiment 31. A method according to any one of Embodiments 26-30, wherein:

part of the liquid medium discharged from the loop reaction zone is discharged at a space velocity proportional to the amount of inorganic acid and alkali metal silicate loaded into the loop reaction zone; and steps (a)-(c) are carried out in a continuous loop reactor.

Embodiment 32. The method of any one of Embodiments 26-31 wherein the liquid medium is recirculated through the loop reaction zone at a rate ranging from about 15 to about 150 L/min.

Embodiment 33. A method according to any one of Embodiments 26-32, wherein the liquid medium is recycled through the loop reaction zone at a rate ranging from about 50 to about 1000 rpm.

Option implementation 34. The method corresponding to any of the embodiments 26-33, in which stage (b) recycle the entire liquid medium or more than 95 wt. % liquid medium.

Embodiment 35. The method of any one of Embodiments 26-34, wherein step (b) is carried out at a temperature ranging from about 85°C to about 100°C.

Embodiment 36. The method according to any one of Embodiments 26 to 35, further comprising a pH adjustment step after step (c), a filtration step after step (c), a washing step after step (c). c) a drying step, or any combination thereof.

Embodiment 37. The method according to any of Embodiments 26-36, wherein the silica particles are:

(i) a median particle size d50 greater than or equal to about 6 microns;

(ii) a ratio (d90-d10)/d50 ranging from about 1.1 to about 2.4;

(iii) the value of IRD at a content of 20 wt. % ranging from about 40 to about 200; And

(iv) a sphericity coefficient (S ₈₀ ) greater than or equal to about 0.9.

Embodiment 38. Silica particles produced by a method according to any one of Embodiments 26-37.

Embodiment 39. The silica particles according to Embodiment 38, wherein the silica particles are precipitated silica particles.

Embodiment 40. The silica particles according to Embodiment 38 or 39, wherein the silica particles are amorphous.

Claims (52)

1. Particles of silicon dioxide, characterized by: (i) median particle size d50 ranging from 8.8 to 15 µm; (ii) a (d90-d10)/d50 ratio value ranging from 1.1 to 2.0; (iii) the value of RDI when the content of particles of silicon dioxide in the toothpaste composition, constituting 20 wt.%, ranging from 70 to 200; (iv) an oil absorption ranging from 30 to 62 cm ³ /100 g; (v) a bulk density after compaction ranging from 52 to 65 lb/ft ³ ; (vi) the value of the peeling index (FOR) at a content of 20 wt.%, in the range from 80 to 110; And (vii) a sphericity coefficient (S ₈₀ ) greater than or equal to 0.9. 2. Particles of silicon dioxide according to claim 1, where: (i) the median particle size d50 is in the range from 8.8 to 15 microns; or (ii) the value of the ratio (d90-d10)/d50 is in the range from 1.1 to 2; or (iii) the value of RDI when the content of particles of silicon dioxide in the composition of the toothpaste, constituting 20 wt. %, is in the range from 70 to 190, for example from 85 to 180; or (iv) the oil absorption is in the range from 30 to 62 cm ³ /100 g; or (v) bulk density after compaction is in the range of 52 to 60 lb/ft ³ ; or (vi) the value of the FOP at a content of 20 wt. % is in the range from 80 to 110; or (vii) the sphericity coefficient (S ₈₀ ) is greater than or equal to 0.92, such as greater than or equal to 0.94; (viii) the silica particles are further characterized by a BET surface (specific surface area determined by the Brunauer-Emmett-Teller method) ranging from 10 to 200 m ² /g, for example from 20 to 100 m ² /g; or (ix) the silica particles are further characterized by a 325 mesh residue less than or equal to 1.2% by weight, such as less than or equal to 0.5% by weight. %; or (x) the silica particles are further characterized by an Einlechner abrasion value ranging from 0.5 to 7 mg loss/100,000 revolutions; or (xi) where the particles of silicon dioxide are particles of precipitated silicon dioxide; or (xii) the silica particles are amorphous or have any combination of these characteristics. 3. Composition of toothpaste containing particles of silicon dioxide according to any one of paragraphs. 12. 4. Composition for caring for teeth containing particles of silicon dioxide according to any one of paragraphs. 12. 5. Composition for caring for teeth, containing from 0.5 to 50 wt.% particles of silicon dioxide according to any one of paragraphs. 12. 6. Composition for caring for teeth according to claim 5, containing from 5 to 35 wt. % silica particles. 7. Composition for caring for teeth according to any one of paragraphs. 4, 5, where the composition further comprises at least one of the following: a humectant, solvent, binder, therapeutic agent, chelating agent, thickener other than silica particles, surfactant, abrasive other than silica particles, sweetener, coloring agent, flavoring agent and preservative, or any combination thereof. 8. The method of obtaining particles of silicon dioxide according to any one of paragraphs. 1, 2, the method includes: (a) continuously feeding the inorganic acid and alkali metal silicate into a loop reaction zone containing a liquid medium stream in which at least a portion of the inorganic acid and alkali metal silicate react to form silica particles in the liquid medium contained in the loop reaction zone ; (b) continuous recirculation of the liquid medium through the loop reaction zone, where the loop reaction zone includes a stator screen with holes having a cross-sectional area equal to more than 3 mm ² or the shear frequency in the loop reaction zone is less than 1,000,000 interactions/min, or both , and other; And (c) continuously discharging from the loop reaction zone a portion of the liquid medium containing silica particles, characterized in that the resulting silica particles have: median particle size d50 ranging from 8.8 to 15 µm; the value of the cleaning index from the film (POP) at a content of 20 wt. % ranging from 80 to 110; the value of RDI when the content of particles of silicon dioxide in the composition of the toothpaste, constituting 20 wt. % ranging from 70 to 200; sphericity coefficient (S ₈₀ ) greater than or equal to 0.9; And bulk density after compaction ranging from 52 to 65 lb/ft ³ . 9. The method of claim 8, wherein steps (a) to (c) are carried out simultaneously. 10. The method according to any one of paragraphs. 8, 9, wherein the loop reaction zone includes a continuous circulation loop of one or more loop reactor tubes. 11. The method according to any one of paragraphs. 8-10, in which: inorganic acid and alkali metal silicate are loaded into the loop reaction zone at different positions of the loop reaction zone; the inorganic acid includes sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, or a combination thereof, and the alkali metal silicate includes sodium silicate. 12. The method according to any one of paragraphs. 8-11, in which the liquid medium is recycled through the loop reaction zone at a pH value ranging from 6 to 10. 13. The method according to any one of paragraphs. 8-12, in which: part of the liquid medium discharged from the loop reaction zone is discharged at a space velocity proportional to the amount of inorganic acid and alkali metal silicate loaded into the loop reaction zone; and steps (a)-(c) are carried out in a continuous loop reactor. 14. The method according to any one of paragraphs. 8-13, wherein the liquid medium is recirculated through the loop reaction zone at a rate ranging from 15 to 150 L/min. 15. The method according to any one of paragraphs. 8-14, wherein the liquid medium is recycled through the loop reaction zone at a rate ranging from 50 to 1000 rpm. 16. The method according to any one of paragraphs. 8-15, in which stage (b) recycle the entire liquid medium or more than 95 wt. % liquid medium. 17. The method according to any one of paragraphs. 8-16, in which stage (b) is carried out at a temperature in the range from 85 to 100°C. 18. The method according to any one of paragraphs. 8-17 further comprising a pH adjustment step after step (c), a filtration step after step (c), a washing step after step (c), a drying step after step (c), or any combination thereof. 19. The method according to any one of paragraphs. 8-18 where the silica particles differ: median particle size d50 ranging from 8.8 to 15 µm; a ratio value (d90-d10)/d50 ranging from 1.1 to 2.0; the value of RDI when the content of particles of silicon dioxide in the composition of the toothpaste, constituting 20 wt. % ranging from 85 to 200; And sphericity coefficient (S ₈₀ ) greater than or equal to 0.9.

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