ITMI20110873A1 - BLEACHING COMPOSITION IN THE FORM OF GEL AND ITS USE FOR DENTAL BLEACHING - Google Patents

Description

DESCRIPTION

`` WHITENING COMPOSITION IN THE FORM OF GEL AND RELATIVE USE FOR DENTAL WHITENING ''

The present invention relates to a whitening composition in the form of a gel, and its use for dental whitening.

In recent decades, teeth whitening has become a very widespread practice, which is carried out for purely aesthetic purposes in order to obtain a dentition free of stains and / or altered colors compared to the natural one (the so-called "discolorations").

Teeth whitening treatments are generally carried out only by specialized personnel (the so-called â € œin officeâ € treatments), as they require special manual skills and attention in order to avoid unwanted effects, such as damage to the dental surface and / or mucous membranes. surrounding. In recent years, less aggressive products have also been developed which allow the person concerned to carry out the whitening independently (the so-called â € œhome bleachingâ € treatments).

The choice between the two types of treatment depends on the results to be obtained. In fact, the â € œin officeâ € treatment allows for faster and more evident results as it is made with products containing a higher concentration of whitening agent.

The most common bleaching materials currently on the market have hydrogen peroxide or carbamide peroxide as their main constituent (the latter forms hydrogen peroxide in aqueous environment). Hydrogen peroxide acts through the in situ formation of radicals which are able to oxidize the chromophores present in the tooth, in particular in the interprismatic spaces. These chromophores, having a chemical structure that absorbs visible light, are responsible for the typical "stains" or dental discoloration. The oxidation of the chromophores leads to the formation of substances that do not absorb visible light, thus eliminating unwanted colors.

In order to accelerate the decomposition of hydrogen peroxide, it is known to add an activator to the whitening composition. The most commonly used activator is sodium hydroxide or other strong base. It is in fact known that hydrogen peroxide chemically decomposes when it is found in aqueous solution at high pH, such as that generated by a strong base, with the formation of hydroperoxianion (OOH <â € “>), which, being unstable to Basic pH, gives rise to water and nascent oxygen, which acts as a strong oxidant.

For example, in US patent 6,986,883 a system for teeth whitening is described which comprises two components: the first is a gel containing a combination of hydrogen peroxide and carbamide peroxide and having a pH value from 5 to 8 , while the second is a gel containing as activator a base, for example sodium or potassium hydroxide, and having a pH value from 9 to 10. As gelling agents, cellulosic derivatives or fumed silica can be used.

The whitening speed obtainable using a strong base as activator is however relatively low, so long maintenance times of the whitening composition on the teeth are required (usually more than 60 minutes), with obvious disadvantages for the user.

Another activator that is able to accelerate the decomposition of hydrogen peroxide is titanium dioxide (TiO2), which is a semiconductor metal oxide with photocatalytic properties, that is, it is able to absorb radiation in the visible ultraviolet field and to interact with hydrogen peroxide in order to favor the formation of highly oxidizing radical species.

For example, in patent application EP 1 048 291 A1 a method for tooth whitening is described which comprises applying titanium dioxide powder in the form of a solution or paste and a hydrogen peroxide solution on the tooth surface, and then obtaining the whitening action by irradiation, in particular with visible light. The hydrogen peroxide solution has a low concentration, generally less than 6%, preferably less than 3%.

In US patent 6,843,981 a dental whitening composition is described which comprises titanium dioxide as activator, hydrogen peroxide or a compound capable of generating hydrogen peroxide when placed in aqueous solution, and a thickening agent in an amount from 1 to 5% by weight with respect to the weight of the composition. A clayey mineral with a lamellar structure is preferably used as a thickening agent. This composition is applied to the tooth and then irradiated with radiation having a wavelength of at least 300 nm.

Finally, patent application EP 1375 635 relates to a composition for dental whitening which comprises a peroxide and a photocatalyst which can be activated with a light radiation having a wavelength greater than or equal to 420 nm. The photocatalyst is in particular titanium dioxide in the anatase form, possibly mixed with the amorphous form. This titanium dioxide is characterized by ESR spectroscopy. The composition can be applied in the form of a solution or gel. No indication is given on the composition of the gel.

The Applicant has posed the problem of obtaining a whitening composition in the form of a gel that can be easily applied in a safe way, so as to avoid undesirable effects on the dental surface and the anatomical environment, and which requires relatively little maintenance times in situ. shorter than what is available on the market today, with an evident whitening effect and as long-lasting as possible. This composition also requires high stability over time, so as to maintain its characteristics even after months of preparation. In fact, the Applicant has found that the most common gelling agents used in the pharmaceutical and cosmetic fields, such as for example acrylic polymers cross-linked with polyalkenyl ethers or glycols, known commercially under the brand name Carbopol ï ››, are not very stable in the presence of highly effective agents. oxidants such as hydrogen peroxide, which over time determines a significant reduction in the molecular weight of the polymer and therefore in the viscosity of the gel, such as to compromise its rheological characteristics.

The Applicant has now found that this and other objectives better illustrated below can be achieved by means of a gel comprising hydrogen peroxide, or a compound capable of generating hydrogen peroxide in an aqueous environment, and titanium dioxide as activator, in which it is present as gelling agent at least one cross-linked polymer containing sulphonic groups, as better defined hereinafter. This gel is stable over time even using high quantities of hydrogen peroxide, providing a product that is easy to apply and has good adhesive properties with respect to the dental surface.

According to a first aspect, the present invention therefore relates to a whitening composition in the form of a gel comprising:

(a) hydrogen peroxide, or a compound capable of generating hydrogen peroxide in an aqueous environment;

(b) titanium dioxide as activator;

(c) at least one cross-linked polymer containing sulfonic groups as a gelling agent.

In a second aspect, the present invention relates to a dental whitening kit which separately comprises:

(i) a first component in the form of a gel which comprises: hydrogen peroxide, or a compound capable of generating hydrogen peroxide in an aqueous environment; and at least one cross-linked polymer containing sulfonic groups as a gelling agent;

(ii) a second component which comprises titanium dioxide as an activator.

According to another aspect, the present invention relates to the use of a whitening composition in the form of a gel as defined above for dental whitening. As regards the gelling agent (c), this is preferably a copolymer between at least one (meta) acrylamide substituted with a sulphonic group and at least one N-vinylamide or N- (1-methyl) vinylamide. This (meta) acrylic copolymer also comprises a small quantity of repetitive units with a cross-linking function deriving from at least one comonomer containing at least two olefinic groups.

In the context of this specification and the claims that follow, the words "(meta) acrylic", "(meta) acrylate" and similar expressions are to be understood as abbreviated expressions that include both acrylates and methacrylates, whereby, for example, "( meta) acrylic "is to be understood as" acrylic or methacrylic ".

In the context of the present description and of the following claims, the term "sulphonic group" means a -SO3X group, where X is selected from: hydrogen ion or, preferably, an alkaline or alkaline-earth metal ion, possibly an ammonium ion alkylated.

Even more preferably, the gelling agent (c) is a (meta) acrylic copolymer containing:

(i) from 1 to 50% by weight, preferably from 2 to 30% by weight, of repetitive units of the formula:

â € "(CH2-CR) â €"

(THE)

R1â € ”NCOR2

where: R is hydrogen or methyl; R1 and R2, the same or different from each other, are selected from: hydrogen, alkyl or alkenyl having from 1 to 30, preferably from 1 to 12, carbon atoms, or R1 and R2 are joined together to form a lactam ring;

And

(ii) from 49.99 to 98.99% by weight, preferably from 69.5 to 97.5% by weight, of repetitive units of the formula:

â € "(CH2-CR ') â €"

(II) CO-NH-Z-SO3X

where R 'is hydrogen or methyl; Z is an alkylene having from 1 to 12, preferably from 1 to 8, carbon atoms; X is chosen from: hydrogen ion or, preferably, an alkaline or alkaline-earth metal ion, ion -N <+> R3R4R5R6, where R3, R4, R5, R6, the same or different from each other, are hydrogen or C1 alkyl -C4;

(iii) from 0.01 to 5% by weight, preferably from 0.5 to 2% by weight, of repetitive units with cross-linking function deriving from at least one comonomer containing at least two olefin groups.

As regards the repetitive units of formula (I), these are preferably derived from: N-vinylformamide, N-vinylpyrrolidone, or their mixtures.

As regards the repetitive units of formula (II), these are preferably derived from: 2-acrylamido-2-methylpropane sulfonic acid or its salts.

As regards the repetitive units with cross-linking function, these are preferably derived from: allyl (meth) acrylate, dipropylene glycol diallylether, polyglycol diallylether, triethylene glycol divinyl ether, hydroquinone diallylether, tetraalloxyethane, tetraethylene glycol diacrylate, triallyl acryletheramide, trimlylethylene diethylene, di their blends.

Preferably, the gelling agent (c) has a Brookfield viscosity, measured in 1% solution in deionized water at 20 ° C according to DIN EN ISO 25555, from 48000 to 65000 mPas.

Further details on these gelling agents (c) and their synthesis are available, for example, in US 6,355,752 and US 6,437,068. Products of this type can be found on the market under the brand name Aristoflex â „¢ (Clariant GmbH).

In a preferred embodiment, said at least one cross-linked polymer containing sulphonic groups (c) is present in the composition according to the present invention in an amount from 1 to 12% by weight, more preferably from 2 to 8% by weight, compared to the overall weight of the composition. It should be noted that these quantities are relatively low compared to the most common gelling agents, such as Carbopol â „¢, which are generally used in quantities greater than 15-20% by weight.

It should be noted that the quantities of the various components of the composition according to the present invention are expressed, except where indicated otherwise, as% by weight with respect to the total weight of the composition in the form of a gel ready for application. As regards component (a), this can be hydrogen peroxide, or a compound capable of generating hydrogen peroxide in an aqueous environment, in particular an inorganic peroxide chosen, for example, from: perborate, percarbonate, persulfate, superphosphate; or also carbamide peroxide.

Component (a), i.e. hydrogen peroxide or a compound capable of generating hydrogen peroxide in an aqueous environment, is preferably present in the composition according to the present invention in an amount from 2 to 50% by weight, more preferably from 20 to 40% by weight, this quantity being expressed as the quantity of hydrogen peroxide obtained from the compound in aqueous solution.

As regards component (b), this is preferably titanium dioxide containing mainly titanium dioxide in anatase form. Preferably, the titanium dioxide is in nanometric form, i.e. with an average particle size lower than 200 nm, more preferably from 5 to 60 nm.

Titanium dioxide suitable for the realization of the present invention is available on the market, for example under the brand name Aeroxide â „¢ of the company Evonik Degussa GmbH, and is generally obtainable by means of a low temperature sol-gel process (generally around 60 ° C) and subsequent calcination at a temperature of around 400 ° C for at least 2 hours.

Component (b), ie titanium dioxide, is preferably present in the composition according to the present invention in an amount of from 0.5 to 10% by weight, more preferably from 1 to 5% by weight.

Preferably, the whitening composition according to the present invention, in its ready-to-use form, has a substantially neutral pH value, that is to say around 7. For this reason it is advisable to add during the preparation of the composition at least a strong base, for example sodium hydroxide and / or potassium hydroxide, in a controlled quantity in order to neutralize the acidity present in the other components, in particular in the gelling agent (c).

Consequently, in the kit according to the present invention, component (ii) preferably further comprises at least one strong base, preferably sodium hydroxide and / or potassium hydroxide.

Said at least one strong base is preferably present in an amount from 1 to 5% by weight, more preferably from 0.5 to 1.5% by weight.

According to a preferred embodiment, the composition in the form of a gel according to the present invention further comprises at least one desensitizing agent, in order to reduce the sensitivity of the tissues and therefore any undesirable effects for the user, generally due to the resulting hypersensitivity from uncovered dentinal tubules or from the movement of the tubular fluid as a result of external stimuli, such as heat, cold, brushing on uncovered collars. As desensitizing agents, for example salts can be used, selected in particular from: potassium nitrate, potassium oxalate, calcium or potassium phosphate, calcium glycerophosphate, or mixtures thereof. Said at least one desensitizing agent is preferably present in the composition according to the present invention in an amount from 1 to 15% by weight, more preferably from 2 to 10% by weight.

According to a preferred embodiment, the composition in the form of a gel according to the present invention further comprises at least one aliphatic polyol, which is capable of improving the consistency of the gel and reducing the opacifying effect deriving from the addition of desensitizing agents as indicated above or other salts. Said aliphatic polyol can be selected, for example, from glycerin, polypropylene glycol, polyethylene glycol, or their mixtures.

Said at least one aliphatic polyol is preferably present in the composition according to the present invention in an amount from 0.5 to 30% by weight, more preferably from 2 to 15% by weight.

The composition in gel form according to the present invention generally comprises water in an amount ranging from 70 to 95% by weight, preferably from 80 to 90% by weight.

The composition in the form of a gel according to the present invention can generally also comprise other minor components, such as flavoring, stabilizers, fluorides (for example sodium monofluorophosphate, sodium fluoride, calcium fluoride or their mixtures) useful for the prevention of dental caries, or also protective of the enamel such as calcium hydroxyapatite.

The composition in the form of a gel according to the present invention is preferably produced as a two-component formulation, which comprises: (i) a first component in the form of a gel which comprises: hydrogen peroxide, or a compound capable of generating hydrogen peroxide in aqueous environment; and at least one cross-linked polymer containing sulfonic groups as a gelling agent; (ii) a second component which comprises titanium dioxide as an activator.

The two components are then combined at the time of application, for example via an open mixer or via a dual syringe.

A two-component formulation as reported above is particularly advantageous as it allows the hydrogen peroxide and the activator to be formulated and stored separately, so that they can be combined only at the time of use. In this way a premature decomposition of the peroxide and therefore a substantial loss of efficacy of the product is avoided. Furthermore, it is possible in this way to formulate the two components in an optimal way taking into account the different chemical-physical characteristics.

In fact, the first component (i) is preferably formulated so as to have a pH value from 4 to 7, more preferably from 5 to 6, since in an acid environment the hydrogen peroxide is more stable over time. It should be noted that the gelling agent (c) as defined above is stable at the pH conditions defined above. On the contrary, other commonly used gelling agents, such as the already mentioned Carbopolï ››, are not very stable at acid pH, as they tend to hydrolyze with a consequent decrease in the molecular weight and therefore in the viscosity of the gel.

On the contrary, the second component (ii) is preferably formulated so as to have a pH value from 11 to 14, more preferably from 12 to 13. In this way, when mixing with the first component (i), it is obtained an increase in the pH value of the latter until the optimum pH values indicated above are obtained for the final composition, with consequent rapid decomposition of the peroxide.

The second component (ii) can be in the form of a solution, dispersion, suspension or gel. Preferably also the second component (ii) is in the form of a gel. In such a case, this further comprises at least one gelling agent. This can be selected from the crosslinked polymers containing sulfonic groups indicated above for the first component (s). However, since the latter are not particularly stable at high pH, it is preferable to use different gelling polymers, having high stability at pH higher than 9, preferably chosen from: carboxymethylcellulose, hydroxypropyl cellulose, cross-linked acrylic polymers (for example the products known commercially under the Carbopol brand â „¢), sodium acrylate copolymers, cellulosic gum, xanthan gum, or their mixtures. Preferably, said at least one gelling agent is present in the second component in an amount from 1 to 12% by weight, more preferably from 2 to 8% by weight, with respect to the total weight of the second component.

As regards the other possible components of the composition according to the present invention as described above, said at least one strong base is added to the second component (ii) so as to obtain, as already explained above, a further activation of the peroxide decomposition reaction . The other components possibly present can be indifferently added to the first and / or second component.

As regards the compositions of the first and second components, these are determined according to the final formulation of the whitening composition in the form of a gel to be obtained, in accordance with the above.

As regards the preparation of the whitening composition in accordance with the present invention, this can be carried out by mixing the various components, together in the case of an extemporaneous preparation to be applied immediately or, preferably, as a two-component formulation in accordance with what is described above. Mixing is typically done at room temperature. In the case of a two-component formulation, the mixing can be carried out starting from the two components present in separate containers, or even through the use of dual double-chamber syringes.

As regards the use of the whitening composition according to the present invention for dental whitening, this can be applied on the teeth by common means, such as spatulas, brushes, etc., possibly with the aid of a dual syringe as indicated above. Before the â € œin officeâ € use, a photo-curing protective mask is required to protect the soft tissues of the mouth.

The composition in accordance with the present invention forms an adherent and homogeneous layer on the tooth, the adhesion being such as to avoid easy removal of the product following contact with the tongue and lips. Naturally, during the permanence of the gel on the teeth, it is advisable for the user to avoid drinking and chewing.

After application on the dental surface, the composition is left to act in place for a time ranging from 10 to 30 minutes, depending on the actual concentration of peroxide present and the whitening effect to be obtained.

To favor the activating action of titanium dioxide, the treated dental surface is preferably irradiated with radiation having a wavelength between 400 and 480 nm, more preferably between 400 and 440 nm. It is important to note that this radiation is in the visible range so it does not require any special precautions, as it would be necessary if a higher frequency radiation (for example UV radiation) were used. The radiation can be generated by a cold light lamp (led, laser, plasma or halogen).

Once the time required for whitening is over, the gel layer can be easily removed with the common means used for oral hygiene, for example by rinsing with water and subsequent brushing with a toothbrush and toothpaste.

It is important to note that the time required for the treatment is significantly shorter than the most common whitening products currently on the market. The reduction of the contact time between the whitening product and the teeth results in a reduction in the possibility of undesirable effects, for example erosion of the dental enamel or triggering of dentinal hypersensitivity.

The present invention will now be further illustrated with some embodiment examples, which are provided for illustrative purposes only but not limitative of the scope of the invention itself.

EXAMPLE

A two-component whitening gel has been prepared. The first component containing hydrogen peroxide had the following composition (% by weight with respect to the total weight of the first component):

Table 1

H2O240.7% in H2O dist. 86%

glycerin 5%

Aristoflex â „¢ AVC <4%>

KNO33%

Potassium oxalate 2%

The hydrogen peroxide in aqueous solution was placed in a reactor equipped with a vacuum pump and potassium nitrate and potassium oxalate salts were added to it, making sure that the stirring was vigorous. Glycerin was then added. After having activated the pump so as to reduce the pressure inside the reactor, the gelling agent Aristoflex â „¢ AVC (cross-linked polymer containing sulphonic groups (copolymer between 2-acrylamido-2-methylpropanesulphonic acid and N-vinylpyrrolidone) was added - Clariant GmbH). The addition of the gelling agent was carried out gradually, waiting each time for its solubilization to be complete. The reduction of the internal pressure was aimed at eliminating any air bubbles formed during gelling of the product.

Once the phase of adding and solubilizing the gelling agent was completed, the product was discharged from the reactor.

The second component containing titanium dioxide was then prepared, having the following composition (% by weight with respect to the total weight of the second component):

Table 2

Aeroxide â „¢ P25 <2%>

H2O dist. 93% Sodium carboxymethylcellulose 4%

NaOH 1%

Demineralized water and titanium dioxide (product Aeroxide â „¢ P25 from Evonik Degussa GmbH) were added to a reactor equipped with a vacuum pump under vigorous stirring.

Sodium hydroxide was then added in the form of a solid flake, and it was verified that the pH value was at least equal to 12 or higher. Finally, the pump was activated in order to obtain a reduction of the internal pressure.

The gelling agent (sodium carboxymethylcellulose - Sigma Aldrich) was subsequently added. The addition of the gelling agent was carried out gradually, waiting each time for its solubilization to be complete. The reduction of the internal pressure had the purpose of eliminating any air bubbles formed during the gelling of the product.

Once the phase of adding and solubilizing the gelling agent was completed, the product was discharged from the reactor.

The two components thus obtained were then mixed using a spatula, with a 4: 1 weight ratio, so as to obtain a concentration of H2O2 equal to 35% by weight.

The whitening gel thus obtained was then applied to a tooth extracted for dental reasons, and kept in place for 20 minutes, under irradiation with an LED lamp (model E-Power LED EP505L-350B1 from Para Light Electronics Co. , Ltd.) having maximum luminous intensity at 460 nm.

After the mechanical removal of the gel, the treated tooth was subjected to microscopic SEM analysis, in order to verify the possible presence of changes in the morphology of the enamel.

The possible demineralization of the dental enamel was instead determined by means of a Vickers microdurometer, in order to establish if there was a change in the hardness of the enamel after the whitening treatment and the subsequent remineralization with an artificial saliva solution.

The most important final test for verifying the effective in vitro whitening action of the gel was performed by analyzing dental sections, before and after treatment, with a SpectroShade Micro spectrophotometer, specific for the determination of any dental discoloration.

A discoloration equal to about 6 average values of the Vita scale was obtained, officially used to evaluate whitening. The starting shade of the tooth was darker than the B3 shade. Numerous whitening tests were carried out using healthy extracted teeth for dental reasons obtaining a significant discoloration allowing to always reach the A2 shade of the Vita scale (6 average values of difference), as can be seen from table 3:

Table 3

whitening gel Gel with 35% by weight of H2O2 applied with activator for 20 minutes with LED lamp average value of

Vita scale post A2

whitening

Î ”E Δ E = 5.7

Î "SGU POST AVERAGE LIFE SCALE Î" medium â ‰ ˆ 6 WHITENING

Dental hardness was also assessed according to the Vickers method before and after the aforementioned whitening treatment. The data are shown in the following table:

Table 4

before after after after contact with whitening artificial saliva whitening hardness

Vickers 17.9 14.1 19.0

From these data it is clear that the whitening treatment implies a certain decrease in dental hardness, which is however totally restored thanks to the remineralizing action of artificial saliva. Artificial saliva, like human saliva, is rich in salts which induce a complete remineralization of the enamel and thus allow to obtain Vickers hardness values even higher than the natives within 24 hours.

Claims (18)

CLAIMS 1. Whitening composition in the form of a gel comprising: (a) hydrogen peroxide, or a compound capable of generating hydrogen peroxide in an aqueous environment; (b) titanium dioxide as activator; (c) at least one cross-linked polymer containing sulfonic groups as a gelling agent. 2. Composition according to claim 1, wherein said at least one gelling agent (c) is a copolymer between at least one (meta) acrylamide substituted with a sulfonic group and at least one N-vinylamide or N- (1-methyl) vinylamide, further comprising a small quantity of repetitive units with a cross-linking function deriving from at least one comonomer containing at least two olefin groups. Composition according to claim 2, wherein said at least one gelling agent (c) is a (meta) acrylic copolymer containing: (i) from 1 to 50% by weight, preferably from 2 to 30% by weight, of repetitive units of the formula: â € "(CH2-CR) â €" (THE) R1â € ”NCOR2 where: R is hydrogen or methyl; R1 and R2, the same or different from each other, are selected from: hydrogen, alkyl or alkenyl having from 1 to 30, preferably from 1 to 12, carbon atoms, or R1 and R2 are joined together to form a lactam ring; And (ii) from 49.99 to 98.99% by weight, preferably from 69.5 to 97.5% by weight, of repetitive units of the formula: â € "(CH2-CR ') â €" (II) CO-NH-Z-SO3X where R 'is hydrogen or methyl; Z is an alkylene having from 1 to 12, preferably from 1 to 8, carbon atoms; X is chosen from: hydrogen ion or, preferably, an alkaline or alkaline-earth metal ion, ion -N <+> R3R4R5R6, where R3, R4, R5, R6, the same or different, are hydrogen or C1 alkyl -C4; (iii) from 0.01 to 5% by weight, preferably from 0.5 to 2% by weight, of repetitive units with cross-linking function deriving from at least one comonomer containing at least two olefin groups. 4. Composition according to claim 3, wherein the repeating units of formula (I) are derived from: N-vinylformamide, N-vinylpyrrolidone, or their mixtures. 5. Composition according to claim 3, wherein the repeating units of formula (II) are derived from: 2-acrylamido-2-methylpropanesulfonic acid or its salts. 6. Composition according to claim 3, wherein the repetitive units with cross-linking function are derived from: allyl (meth) acrylate, dipropylene glycol diallylether, polyglycol diallylether, triethylene glycol divinyl ether, hydroquinone diallylether, tetraalyloxyethane, tetraethylene glycol diacrylate, triallyletheyl ethyl , divinylbenzene, or mixtures thereof. 7. Composition according to any one of the preceding claims, wherein said at least one gelling agent (c) has a Brookfield viscosity, measured in a 1% solution in deionized water at 20 ° C according to DIN EN ISO 25555, from 48000 at 65000 mPas. 8. Composition according to any one of the preceding claims, wherein: component (a) is present in an amount from 2 to 50% by weight, preferably from 20 to 40% by weight, this amount being expressed as the quantity of hydrogen peroxide obtained from the compound in aqueous solution; component (b) is present in an amount from 0.5 to 10% by weight, preferably from 1 to 5% by weight; component (c) is present in an amount from 1 to 12% by weight, preferably from 2 to 8% by weight, with respect to the total weight of the composition. Composition according to any one of the preceding claims, wherein the component (b) is titanium dioxide containing mainly titanium dioxide in anatase form, with an average particle size lower than 200 nm, preferably from 5 to 60 nm. 10. Composition according to any one of the preceding claims, having a substantially neutral pH value, that is to say around 7. Composition according to any one of the preceding claims, further comprising at least one desensitizing agent. Composition according to any one of the preceding claims, further comprising at least one aliphatic polyol, selected for example from: glycerin, polypropylene glycol, polyethylene glycol, or mixtures thereof. 13. Teeth whitening kit which separately includes: (i) a first component in the form of a gel which comprises: hydrogen peroxide, or a compound capable of generating hydrogen peroxide in an aqueous environment; and at least one cross-linked polymer containing sulfonic groups as a gelling agent; (ii) a second component which comprises titanium dioxide as an activator. Kit according to claim 13, wherein the component (ii) further comprises at least one strong base, preferably sodium hydroxide and / or potassium hydroxide. Kit according to claim 13 or 14, wherein the first component (i) has a pH value from 4 to 7, preferably from 5 to 6. Kit according to any one of claims 13 to 15, wherein the second component (ii) has a pH value from 11 to 14, preferably from 12 to 13. Kit according to any one of claims 13 to 16, wherein the second component (ii) is in the form of a gel and comprises at least one gelling agent stable at pH higher than 9, preferably selected from: carboxymethyl cellulose, hydroxypropyl cellulose, polymers cross-linked acrylics, sodium acrylate copolymers, cellulosic gum, xanthan gum, or mixtures thereof. 18. Use of a whitening composition in the form of a gel according to any one of claims 1 to 12 for dental whitening.