The invention refers to a specific composition and method of production to obtain a bioactive calcium phosphates doped with fluoride and hydroxyl compounds, which when in contact with body fluids, as well as aqueous and/or saline solutions are able to transform via a slow- controlled precipitation process, into fluorapatite. The technical sector and application of such an invention are related to oral health and dentistry.

BACKGROUND OF THE INVENTION

The mineral component of human dental enamel is basically calcium-deficit carbonate hydroxyapatite. Carbonated calcium hydroxyapatite is more soluble than calcium hydroxyapatite, particularly in acidic media. The pure hydroxyapatite [Ca ₁₀ (PO ₄ )6(OH) ₂ ] allows the incorporation of many ions that fit into the crystalline structure and affect its solubility. The substitution in the hydroxyapatite crystal occurs during development with carbonate, magnesium, fluoride, etc. Fluoride improves the quality of mineralized tooth tissues in general, by reducing the relative amounts of carbonated apatite. The reaction between hydroxyapatite and low concentrations of fluoride has been postulated to be an ionic exchange, in which fluoride replaces and assumes the positions of the hydroxyl ions in the crystal lattice structure. The replacement of hydroxyl groups with the smaller fluoride ions should result in a more stable apatite structure. If the OH- ion in the pure hydroxyapatite is completely replaced by a fluoride ion (F-) the resulting mineral is fluorapatite [Ca ₁₀ (PO ₄ )6F ₂ ]. However, pure fluorapatite can practically never be found. Only 10% of the hydroxyl groups can be substituted by fluoride in the surface enamel. The main mineral phase of permanent dentin is also hydroxyapatite. Dentin contains (by volume) 47% apatite, 33% organic components and 20% water. The crystallites have much smaller dimensions than those found in enamel, which makes dentine more susceptible to caries attack than enamel. Smaller crystallites dissolve faster when placed in an under-saturated solution. The organic matrix is mainly composed of collagen. It forms the backbone of dentin and serves as a template for the deposition of apatite crystallites within the collagen helix.

Dental caries typically starts at and below the enamel surface (the initial demineralisation is subsurface) and is the result of a process where the crystalline mineral structure of the tooth is demineralized by organic acids produced by biofilm bacteria from the metabolism of dietary fermentable carbohydrates, primarily sugars. Although a wide range of organic acids can be generated by dental biofilm microorganisms, lactic acid is the predominant end product from sugar metabolism and is considered to be the main acid involved in caries formation. As acids build up in the fluid phase of the biofilm, the pH drops to the point where conditions at the biofilm- enamel interphase become undersaturated and acid demineralizes the tooth mineral so the surface layer of the tooth is partially demineralized. The loss of mineral leads to increased porosity, widening of the phases between the enamel crystals and softening of the surface, which allows the acids to diffuse deeper into the tooth resulting in demineralization of the mineral below the surface (sub-surface demineralization). The build-up of reaction products, mainly calcium and phosphate, from the dissolution of the surface and sub-surface raise the degree of saturation and can partially protect the surface layer from further demineralization. Also, the presence of fluoride can inhibit the demineralization of the surface layer. Once sugars are cleared from the mouth by swallowing and salivary dilution, the biofilm acids can be neutralized by the buffering action of saliva. The pH of biofilm fluid returns toward neutrality and becomes sufficiently saturated with calcium, phosphate, and fluoride ions so that demineralization stops and re-deposition of mineral (remineralization) is favored. Due to the dynamic nature of the disease process, the very early (subclinical) stages of caries can be reversed or arrested especially in the presence of fluoride. As demineralization progresses into the subsurface of the enamel and dentin in the case of root caries, with a continuing acid challenge and pH drop the rate of mineral loss becomes greater in the subsurface than at the surface, resulting in the formation a subsurface lesion. When sufficient mineral is lost, the lesion appears clinically as a white spot. This is a clinically important stage of the caries process since the lesion can be arrested or reversed by modifying the causative factors or applying preventive measures; however, the repair process is typically mostly restricted to the surface layer. If the caries process progresses further, the surface porosity increases with the formation of micro-cavitation in enamel or in root caries— a progressive softening of the surface dentin layer. In caries of the tooth crown, the surface layer of the lesion may eventually collapse, resulting in physical cavitation. Even at this more extensive stage of caries severity, a lesion may in optimal circumstances still arrest, although the biofilm retaining cavity will persist. When an irreversible stage of lesion extent is reached, combined with symptoms and/or considerations of the functional or aesthetic needs of the patient, operative intervention is indicated. If the caries process continues eventually the dental pulp will be compromised and either a root canal treatment or a tooth extraction will be necessary.

In extensive lesions, the demineralized tissues are completely removed and replaced with a filling material. However, the development of adhesive techniques without the need for mechanical retention has allowed dentists to adopt a more tooth-preserving approach. Yet low- quality evidence suggests that resin composites lead to higher failure rates and risk of secondary caries than amalgam restorations. Via the stepwise or partial caries removal, in which only the superficial layers of the lesions are removed, it is possible to reduce the incidence of pulp exposure and favor caries arrest and tertiary dentin formation (that is, laying down new protective dentin in response to an advancing caries lesion in both primary and permanent teeth). Although these techniques show a clinical advantage over complete caries removal, it is too early to recommend certain clinical strategies. It must also be underlined that the decayed teeth must be vital and free from symptoms. Furthermore, the success depends on an appropriate restoration that completely seals the tooth and keeps remaining bacteria in the deeper dentin layers.

The benefits of fluoride on caries prevention and arrest are generally accepted by dental researchers and practicing professionals worldwide. These include community-based methods of fluoride delivery (e.g. water fluoridation) and a broad range of fluoride agents (paste, gel, foam, rinse, solution, varnish, drops, tablets). The use of fluorides in kinds of toothpaste is credited with the overall global reduction in caries in many countries over recent decades as toothbrushing with toothpaste is so widely accepted as a behavioral norm associated with both health and grooming. The preventive contribution of the fluoride toothpaste outweighs that from brushing per se. Flossing is practiced to a very variable extent and the evidence for a caries preventive effect is limited. Fluoride can be available in various formulations: i) sodium fluoride (NaF), ii) acidulated fluorophosphates (APF); iii) stannous fluoride (SnF2). Fluoride toothpaste is the most widely used form of fluoride source worldwide. Fluoride dentifrices (fluoride containing paste) have shown in numerous clinical trials to be effective anticaries agents. The benefit is seen to be derived from the frequent low dose applications. Topical fluoride use at high concentrations (>2,500ppm) provides the driving force to penetrate the dental biofilm adjacent to the tooth surface, delivering fluoride to the tooth surface and more importantly concentrates it in incipient lesions. At these levels, fluoride is shown to decrease rate of enamel demineralization and increased rate of enamel remineralization. There is also a relationship between higher fluoride concentration and prolonged retention of fluoride in the oral cavity. High fluoride levels are necessary for the formation of fluoride reservoir (calcium fluoride-like deposits) on the tooth surface and in dental plaque. Very high fluoride levels can also have a transient bactericidal effect, but this would require repeated frequent applications of professionally applied high concentration fluoride which is not practical

Bioactive materials are nowadays frequently used for bone regeneration as well as in preventive and restorative dentistry, especially when such bioactive substances are incorporated in dental composites, adhesives, endodontic cements. Moreover, bioactive materials are of key importance in dental cosmetic and prevention products such as toothpaste, mouthwash and remineralizing treatments for dentin and enamel (e.g. gel, varnish, creams and light-curing sealers) for enamel and dentin.

Dental caries is a biofilm-mediated, sugar-driven, multifactorial, dynamic disease that results in the phasic demineralization and remineralization of dental hard tissues. Caries can occur throughout life, both in primary and permanent dentitions, and can damage the tooth crown and, in later life, exposed root surfaces. The balance between pathological and protective factors influences the initiation and progression of caries. This interplay between factors underpins the classification of individuals and groups into caries risk categories, allowing an increasingly tailored approach to care. Dental caries is an unevenly distributed, preventable disease with considerable economic and quality-of-life burdens. The daily use of fluoride toothpaste is seen as the main reason for the overall decline of caries worldwide over recent decades. Moreover, fluoride-containing products are also commonly used in oral hygiene and preventive/restorative dentistry. Indeed, fluoride ions may replace the hydroxyl groups present in dental hydroxyapatite, transforming this latter into fluorapatite; this makes dental enamel more resistant to acid attacks (e.g. erosion) and caries (primary and secondary lesions). Fluorapatite is recognized as the toughest biological apatite in the animal world, and also as the material with the highest resistance to dissolution in acidic media (e.g. cariogenic bacteria demineralize the tooth and create the carious lesion via organic acids produced by their metabolisms in the presence of simple and complex sugar).

The invention refers to a composition for obtaining a bioactive material, preferably in powder, containing fluoride and a pH regulator. This causes a reaction that, if not manipulated, would result in the formation of brushite. In particular, it is the combination of a first component and a second component that, when reacted, would generate brushite or other types of calcium phosphates, but that when the pH of the reaction is maintained under control, the formation of brushite is inhibited, nut instead a precursor of fluoride-doped hydroxyapatite is formed; this latter gradually transform into fluorapatite.

Several patents based on compositions for a bioactive material comprising fluoride are already present around the world. Among the closest to our invention, there is a patent, US4775646, which is made of Si02, CaO, Na ₂ 0, P ₂ 0 ₅ (Bioactive Glasses).

A further patent with the same characteristics to our invention is US2013/0171220, which refers to a composition for a bioactive material comprising one or more bioactive glasses Si02, P205 and fluoride.

Moreover, patent US 2012128566 provides a method of preparation of fluorapatite, in which tetracalcium phosphate, monocalciumhydrogen phosphate and sodium fluoride are mixed together with water and phosphoric acid to form a cement of fluorapatite in a period of 1 to 3 days. However, such a rapid formation of fluorapatite may prevent all pores of the enamel to be repaired, obtaining a sub-optimal remineralisation of the dental tissues (e.g. enamel and dentin).

Unlike the latest patents cited above, our invention is much less complex in its composition because it is not a bioactive glass but a modified calcium/phosphate. In addition, this invention is of lower economic cost and the procedure for obtaining it is very simple.

DESCRIPTION OF THE INVENTION

Conversely, with this invention we are proposing, two types of fluoride salts and a pH regulator as main components able to“slows down” the formation of fluorapatite and generating benefits by allowing a more adequate and precise filling/repair of all porosities present in demineralized dental tissues, such as enamel and dentin. In this way, it might be possible to obtain dental surface harder and more resistant to acid attacks and dental caries.

The composition comprises: A. A first component including at least one of the following compounds: calcium-deficient phosphate-tricalciumphosphate, tricalcium phosphate, tetracalcium phosphate, oxyapatite, hydroxyapatite.

B. A second component including at least one of the following compounds: monocalcium phosphate monohydrate or any other calcium acid phosphate such as calcium dihydrogen phosphate (Synonym: monobasic calcium phosphate, monocalcium orthophosphate, monocalcium phosphate, calcium biphosphate, calcium acid phosphate) or also meta-phosphoric acid and/or ortho-phosphoric acid.

C. Two fluoride-releasing molecules.

D. A pH regulator

As for fluoride-releasing molecules, calcium fluoride and sodium fluoride have been successfully tested, although there may be other fluoride-releasing molecules that can be used in the composition.

On the other hand, the pH regulator tested and employed in this invention to attain the optimal results is calcium hydroxide, although it is not ruled out that there may be other pH regulators equally effective.

Calcium hydroxide is optimal as an element to maintain a neutral/alkaline pH to prevent the formation of brushite when beta-tricalcium-phosphate and monocalcium monohydrogenated phosphate react when mixed in the presence of water. Our invention leads to the formation of a highly reactive fluoride-doped calcium phosphate that initially transforms into nanohydroxyapatite and over a period of approximately 20-30 days, due to an exchange of OH ions with fluoride ions, it transforms into compact nano-fluorapatite on the outer surface of the tooth. As anticipated above, this transformation occurs due to a slow and controlled reaction due to hydroxyl ions (OH) from calcium hydroxide, which is more available in the first days of storage in artificial saliva than fluoride ions, which begin slowly incorporated in place after replacing of OH ions present in the pre-formed, above cited, nanohydroxyapatite.

Indeed, nano-hydroxyapatite is formed first and then with the dissolution of more fluoride ions during storage in water or body fluid solutions, the OH groups of hydroxyapatite are replaced with fluoride ions and nono-fluorapatite forms. These results can be seen in the x-ray analysis in the picture enclosed in this document.

On the other hand, the use of calcium hydroxide slows the formation of fluorapatite because the apatite crystals generated are deposited nanometrically and grow slowly so that they are able to fill all the nano-porosities of the demineralized enamel.

The process by which this bioactive material is prepared and obtained is divided into the following stages:

1.- Mixing stage:

At this mixing stage, a homogeneous mixture of: - 30-60 wt% of the first component.

- 30-60 wt% of the second component.

- 5-40 wt% of a pH regulator, such as calcium hydroxide

1-30 wt% fluoride-releasing molecules, such as sodium fluoride or calcium fluoride.

The best results are obtained if the percentage of the first component and the second component are similar. A similar scenario will be obtained when the percentage between first and the second component does not exceed 40%.

2.- Hydration stage:

In this second stage of hydration, the mixture obtained in the first stage is incorporated in the moisturizing element. This moisturizing agent may be distilled water or any other type of aqueous and saline solution such as PBS (phosphate buffered saline) containing sodium chloride, sodium phosphate, potassium chloride and potassium phosphate. The use of other solutions is not ruled out.

In particular, a possible proportion to perform this second stage would be:

50 wt% of the mixture obtained in the first stage.

50 wt% moisturizing element, as can be distilled water (optimal moisturizing agent).

The tests have been performed with hydration in which the mixture obtained from the first phase was mixed equally with the moisturizing fluids, although it is not ruled out that other similar percentages can give similar results.

We may aspect similar results as a final product when the percentage difference between the components does not exceed 40% each part.

Reactions, other than those described above, may occur depending on several circumstances and variabilities, although the reactions that have been qualified have been indicated.

This second stage is performed in a period of 1 to 10 minutes, although nothing prevents this phase to take place from being prolonged for longer period of time.

3.- Dehydrated stage.

In this third stage, it will be necessary to remove the moisture from the mixture. One option to remove this moisture is to let the mixture dry at a temperature of 40 °C to 55 °C

(Celsius) for 24 hours in a vacuum dryer containing absorbent silica. This drying option is not the only one, although from the tests carried out it is possible to get an optimal result.

4.- Milling/grinding stage In this fourth stage, the product already dehydrated, is ground to a particle size less than 30 microns (pm); then one can continue with the grinding stage until reaching dimensions from 10 pm to nanosized particles.

The process for obtaining the raw material with which to obtain the bioactive powder is composed of these stages 1 to 4 is described here. The grinding process after the reaction of the previous stages has a specific physical-mechanical function in the prediction process. With this grinding process, a specific granulometry is obtained so that the particles of this bioactive powder can dissolve in specific time lapse in order to obtain gradual and increasing remineralization of the dental tissues. A powder with large or too small granulometry can positively or negatively influence the dissolution of the ions of our bioactive material, and finally, alter the process of remineralization of the hard tissues of the tooth.

That is why there is a first grinding process to homogenize the components, and then a subsequent hydration step which produces the appropriate reaction between components, and finally after the dehydration of that material already reacted, a second grinding step is performed to obtain the granulometry suitable for use.

To obtain the reaction for the formation of apatite enriched with fluoride and/or fluorapatite it is necessary to follow the stage explained below.

5.- Stage of rehydration and bioactive transformation

To obtain the formation of nano-fluorapatite and/or nano-hydroxyapatite enriched with fluoride is necessary a further stage that includes the contact of these powders with distilled water or saline solution such as PBS (phosphate buffered saline) or saliva (artificial or biological) (Figure 1 ).

The compound once in contact with biological fluids such as artificial saliva, begins to dissolve and precipitate first in the form of nano-hydroxypatite and slowly and finally (hydration) in nanofluoropatite crystals, which continue to grow until filling all porosities of demineralized dental tissues, creating a super compact and hard mineral layer of fluorapatite (Figure 2).

For instance, at this stage of hydration, the following reactions occur:

The reaction occurs in a time of approximately 15 to 60 days, usually 60 days to attain the maximum conversion of the hydroxyapatite to fluorapatite (Figure 1 and 2). Several applications can be considered for this new material in the field of dentistry. For instance, these can be used to cover the surface of dental implants or creates bioactive composites, adhesives, endodontic cements. Moreover, it can be used as a bioactive active principle for dental prevention and cosmetic products such as toothpastes, mouthwashes and remineralizing treatments or powder for air-abrasion or air-polishing procedures.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

A non-limiting example of an embodiment of the invention will be described below.

The invention refers to a composition for obtaining a bioactive material the material obtained and its application, containing fluoride and a pH regulator that causes the inhibition of the formation of brushite and a precursor of fluoride-doped hydroxyapatite is formed; this latter gradually transform into fluorapatite.

The bioactive material reacts with an aqueous and saline solution obtaining fluorapatite or apatite enriched with fluorine, which makes this material especially suitable for use in implants, composites, adhesives, crowns, endodontic cements and also for prevention elements and dental cosmetics such as, toothpastes, rinses or remineralizing treatments among others.

This bioactive compound comprises a first component, in this case beta-tricalcium phosphate, a second component, in this case monohydrogen calcium phosphate anhydrous, fluorine-releasing molecules, in this case sodium fluoride and calcium fluoride, and a pH regulator, specifically calcium hydroxide.

To obtain this biomaterial, the previous composition is reacted keeping the pH controlled so that brushite is not obtained but the biomaterial of interest. For this, the procedure comprises the following stages.

1.- Mixing stage:

At this mixing stage, a homogeneous mixture of:

- 40 wt% of the first component.

- 40 wt% of the second component.

10 wt% of a pH regulator, such as calcium hydroxide.

- 5 wt% of sodium fluoride.

- 5wt% of calcium fluoride.

2.- Hydration stage:

In this second stage of hydration, the mixture obtained in the first stage is incorporated in the moisturizing element in this case distilled water in next proportions.

50 wt% of the mixture obtained in the first stage. 50 wt% distilled water.

This second stage is performed in a period of 1 to 10 minutes.

3.- Dehydrated stage.

In this third stage, it will be necessary to remove the moisture from the mixture. For that purpose the mixture is dried at a temperature of 45 °C (Celsius) during 24 hours and after is used a vacuum dryer containing absorbent silica.

4.- Milling/grinding stage

In this fourth stage, the product already dehydrated, is ground to a particle size less than 30 microns (pm).

The process for obtaining the raw material with which to obtain the bioactive powder is composed of these stages 1 to 4 is described here.

To obtain the reaction for the formation of apatite enriched with fluoride and/or fluorapatite it is necessary to follow the stage explained below.

5.- Stage of rehydration and bioactive transformation

To obtain the formation of nano-fluorapatite and/or nano-hydroxyapatite enriched with fluoride is necessary a further stage that includes the contact of these powders with distilled water or saline solution such as PBS (phosphate buffered saline) or saliva (artificial or biological) (Figure 1 ).

The compound once in contact with biological fluids such as artificial saliva, begins to dissolve and precipitate first in the form of nano-hydroxypatite and slowly and finally (hydration) in nanofluoropatite crystals, which continue to grow until filling all porosities of demineralized dental tissues, creating a super compact and hard mineral layer of fluorapatite (Figure 2).

For instance, at this stage of hydration, the following reactions occur:

Ca ₃ (P0 ₄ ) ₂ + Ca(H ₂ P0 ₄ ) ₂ . H ₂ 0+ CaF ₂ + NaF + NaOH 1/2Ca^> ₁₀ (PO ₄ ) ₆ F ₂ + 2HF + Na ₂ H(P0 ₄ ) +2H ₂ Or

The reaction occurs in a time of approximately 15 to 60 days, usually 60 days to attain the maximum conversion of the hydroxyapatite to fluorapatite (Figure 1 and 2).

Several applications can be considered for this new material in the field of dentistry. For instance, these can be used to cover the surface of dental implants or creates bioactive composites, adhesives, endodontic cements. Moreover, it can be used as a bioactive active principle for dental prevention and cosmetic products such as toothpastes, mouthwashes and remineralizing treatments or powder for air-abrasion or air-polishing procedures.