Fluorohydroxyapatite is also known as fluorapatite.

The amount of fluoride and fluorine in bones is influenced by several factors, including age.  Fluoride is incorporated in teeth, bones and, by replacing the hydroxyl ion in hydroxyapatite, fluorohydroxyapatite is formed, which is present for example in tooth enamel.

 is a mineral similar to hydroxyapatite, a form of calcium phosphate naturally found in teeth and bones, but with added fluoride. This ingredient is widely used in oral care products, such as toothpaste and dental treatments, for its remineralizing and strengthening properties. Fluorohydroxyapatite helps reinforce tooth enamel, prevent cavities, and promote the repair of small dental lesions.

Chemical Composition and Structure
Fluorohydroxyapatite is a variant of hydroxyapatite where some hydroxide ions (OH-) are replaced by fluoride ions (F-). This substitution enhances the acid resistance of fluorohydroxyapatite, improving its ability to protect teeth from demineralization and acid attacks produced by bacteria.

Physical Properties
Fluorohydroxyapatite appears as a fine white powder, soluble in acids but insoluble in water. It has a crystalline structure similar to tooth enamel, allowing it to naturally bond to the tooth surface and integrate into the remineralization process.

Production Process
Fluorohydroxyapatite is synthetically produced through a reaction involving calcium, phosphate, and fluoride compounds under controlled conditions. This process replicates the chemical and physical structure of the material found in teeth, making it suitable for use in oral health products.

• Hydroxyapatite - Hydroxyapatite is a naturally occurring mineral form of calcium phosphate. It serves as the main raw material for the synthesis of fluorohydroxyapatite. Hydroxyapatite can be obtained from various sources, including bone or synthesized through chemical processes.
• Fluoride compounds - Fluoride compounds, such as sodium fluoride or ammonium fluoride, are used as sources of fluoride ions in the synthesis of fluorohydroxyapatite. These compounds provide the necessary fluorine ions for the substitution of hydroxyl ions in hydroxyapatite.

The synthesis process takes place in several stages:

• Preparation of Precursors. Precursors are prepared, typically calcium nitrate tetrahydrate (Ca(NO3)2.4H2O), phosphorus pentoxide (P2O5) and ammonium fluoride (NH4F). These provide calcium, phosphorus, and fluorine components, respectively.
• Sol-Gel process. The precursors are mixed in a solvent to form a sol, a colloidal suspension of solid particles. The sol is then gelled to form a solid net, capturing the liquid component within its structure.
• Spin Coating. The sol is deposited on a substrate, such as titanium, and then spun at high speed to spread the sol evenly across the substrate and form a thin film.
• Heat treatment. The coated substrate is heated (fired) to temperatures between 500 and 800 ºC. This process, known as calcination, helps to consolidate the film and improve its crystallinity, forming fluorohoxyapatite.
• Characterization. The final product is characterized using techniques such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to confirm the formation of fluorohydroxyapatite.

What it is used for and where

Medical

Drug delivery systems: fluorohydroxyapatite nanoparticles have been studied as carriers for controlled drug delivery. These nanoparticles can encapsulate therapeutic agents and release them in a controlled manner, enabling localised and sustained drug delivery to the desired site.

Bone grafts and tissue engineering: fluorohydroxyapatite has been explored as a material for bone grafts and scaffolds in tissue engineering applications. Its biocompatibility and similarity to natural bone mineral make it suitable for promoting bone regeneration and integration with surrounding tissues.

Dentistry

Dental coatings and surface treatments: fluorohydroxyapatite coatings can be applied to dental implants, orthodontic brackets and other dental devices to improve their biocompatibility and osseointegration (the bonding of the implant to the surrounding bone). The addition of fluoride in fluorohydroxyapatite coatings can provide antimicrobial properties and prevent biofilm formation.

Enamel repair and remineralisation: fluorohydroxyapatite has the ability to promote remineralisation and repair of enamel. When incorporated into oral hygiene products such as toothpaste or mouthwash, it can help prevent caries, strengthen tooth enamel and reduce the risk of caries.

Dental fillings and restorations: fluorohydroxyapatite can be used as a component in dental composites and prosthetic materials. It provides improved mechanical properties, better wear resistance and greater resistance to acid attack than conventional materials. These properties make fluorohydroxyapatite  a suitable material for dental fillings, crowns and other dental restorations.

Cosmetics

Oral care agent. This ingredient can be placed in the oral cavity to improve and/or maintain oral hygiene and health, to prevent or improve a disorder of the teeth, gums, mucous membrane. It provides cosmetic effects to the oral cavity as a protector, cleanser, deodorant.

Health and Safety Considerations

Safety in Use
Fluorohydroxyapatite is considered safe for use in oral care products. It is well tolerated and does not cause significant side effects when used as directed. It is not known to cause irritation or allergic reactions.

Allergic Reactions
Allergic reactions to fluorohydroxyapatite are extremely rare. However, individuals with sensitivities to similar ingredients should consult a healthcare provider before use.

Toxicity and Carcinogenicity
There is no evidence that fluorohydroxyapatite is toxic or carcinogenic. It is widely used in oral care products and considered a safe ingredient when used within approved concentrations.

Environmental and Safety Considerations
As a synthetic mineral, fluorohydroxyapatite is biodegradable and poses no significant environmental threat. The production process, when managed properly, has a limited environmental impact.

Regulatory Status
Fluorohydroxyapatite is approved for use in oral care products in many regions, including the European Union and the United States. It is regarded as a safe and highly effective ingredient for cavity prevention and enamel strengthening.

Studies

Fluorohydroxyapatite is a mineral composed of fluo and hydroxyapatite. Hydroxyapatite is a mineral composed mainly of calcium and is present in the human body and milk in good quantities and is found in bones and teeth where it acts as a shield for caries. However, when used as a food additive, this study on nanoparticles draws consumers' attention to the dangers of prolonged use (1).

Various strategies are used in the prevention of caries, including the use of fluoride and hydroxyapatite nanoparticles. Two new noninvasive repair techniques using fluorohydroxyapatite crystals are described here (2).

Nanoparticles of fluorohydroxyapatite in combination with polyetheretheretherketone led to an improvement in the use of polyetheretheretherketone, a good component, but which had shown little binding capacity with natural bone tissue and lack of antibacterial activity (3).

Studies and insights on fluorohydroxyapatite

References_________________________________________________________________________

(1) Setyawati MI, Sevencan C, Bay BH, Xie J, Zhang Y, Demokritou P, Leong DT Nano-TiO2 Drives Epithelial-Mesenchymal Transition in Intestinal Epithelial Cancer Cells.  Small. 2018 Jul;14(30):e1800922. doi: 10.1002/smll.201800922.

(2) Clarkson BH, Exterkate RA. Noninvasive dentistry: a dream or reality? Caries Res. 2015;49 Suppl 1:11-7. doi: 10.1159/000380887. Epub 2015 Apr 13. PMID: 25871414.

(3) Wang L, He S, Wu X, Liang S, Mu Z, Wei J, Deng F, Deng Y, Wei S. Polyetheretherketone/nano-fluorohydroxyapatite composite with antimicrobial activity and osseointegration properties. Biomaterials. 2014 Aug;35(25):6758-75. doi: 10.1016/j.biomaterials.2014.04.085.