Hydroxyapatite is the primary mineral component that gives structure and hardness to human bone and teeth. This naturally occurring compound, a form of calcium phosphate, constitutes approximately 97% of tooth enamel, making it the hardest substance in the human body. Nano hydroxyapatite (nHA) is a synthetic version of this mineral, engineered at an ultra-fine scale for use in modern oral care products. This technology was originally developed by NASA in the 1970s for astronauts experiencing mineral loss in zero gravity. Today, nHA mimics the body’s natural processes, offering a direct way to support and reinforce dental structure.
The Chemistry of Nano Hydroxyapatite
Hydroxyapatite has the chemical formula \(\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2\). The effectiveness of nHA in dental products is directly related to its size, which is measured in nanometers (nm). The synthetic particles are typically engineered to be between 20 and 100 nm in size.
This minute size is significant because it closely matches the size of the natural crystallites that make up human tooth enamel. Because nHA is structurally analogous to the natural building blocks of the tooth, it is considered a biomimetic material. This allows the synthetic particles to interact seamlessly with the tooth surface.
How nHA Repairs and Protects Tooth Enamel
The primary function of nHA in oral care is to support the natural repair process of the teeth through remineralization. When acids erode the enamel, they create microscopic defects and leach away calcium and phosphate ions. Applied nHA particles fill these tiny, demineralized areas, integrating directly into the crystal structure to rebuild and strengthen the enamel from within. This process repairs surface damage and creates a smoother surface, making it more difficult for plaque and bacteria to adhere to the tooth.
Reducing Hypersensitivity
The second major function is the reduction of dentin hypersensitivity, which is sharp pain from cold or hot stimuli. Sensitivity occurs when the underlying dentin, which contains thousands of tiny channels called dentinal tubules leading to the nerve, becomes exposed. The nanoscale particles of nHA are small enough to travel into and physically plug these exposed dentinal tubules. This physical barrier blocks external stimuli from reaching the pulp, preventing the pain associated with temperature changes or pressure.
Comparing nHA to Fluoride Treatments
For decades, fluoride has been the standard for preventing tooth decay, but nHA offers a distinct alternative mechanism. Fluoride works by reacting with the tooth’s existing hydroxyapatite to form fluorapatite, a new, harder, and more acid-resistant mineral. This creates a protective layer over the enamel, making it more robust against future acid attacks.
In contrast, nHA operates through a direct repair method, depositing new, synthetic hydroxyapatite crystals directly into the tooth structure to replace lost minerals. Clinical studies often show that nHA is similarly effective to fluoride in remineralizing early-stage cavities.
While fluoride has broad regulatory approval in the United States, nHA has been widely used in Japan since the 1980s and is prevalent in European markets. The acceptance of nHA in these regions is due to its effectiveness in remineralization and its safety profile, which avoids the risk of dental fluorosis caused by excessive fluoride intake during childhood.
Safety Profile and Consumer Use
Although concerns often center on the term “nano,” the material is considered biocompatible, meaning it does not cause harm to living tissues. NHA is non-toxic and is not associated with systemic absorption issues when used in oral care products. This characteristic makes nHA a common choice for children’s toothpaste, as it is safe even if accidentally swallowed.
Regulatory bodies, such as the European Commission’s Scientific Committee on Consumer Safety (SCCS), have evaluated nHA and deemed it safe for use in oral products. The SCCS approves concentrations up to 10% in toothpaste, specifically applying to the rod-shaped particles used in dental products.
Over-the-counter toothpastes containing nHA typically feature concentrations of 10% or less to achieve their remineralizing and desensitizing effects. Beyond daily toothpaste, nHA is also used in higher-concentration professional dental treatments, such as pastes and varnishes applied in a dental office setting.