Your teeth are made of minerals. Around 97 percent of tooth enamel is a calcium phosphate mineral called hydroxyapatite. It is the primary building block of your teeth.

That is what makes it so interesting as an oral care ingredient. When hydroxyapatite is used in toothpaste, it works with your tooth structure. It deposits the same mineral building blocks back onto surfaces that daily acid exposure, food, and brushing gradually strip away.

At Peg Paste, we use  micro-hydroxyapatite. Not nano. Micro. And there is a specific reason for that choice, one grounded in the clinical evidence rather than the marketing landscape.

This is what we found when we followed the research.

When you brush, hydroxyapatite particles are carried to the tooth surface. Several things happen from there, all documented in the published literature.

The particles adhere directly to the enamel surface, filling microscopic surface defects and demineralised pores. Because they share the same mineral composition as the tooth, there is a natural chemical affinity at work.

A 2020 laboratory study grew Streptococcus mutans biofilms, the bacteria most associated with dental caries, and added hydroxyapatite to the system. When the bacteria produced acid, the hydroxyapatite released calcium ions into the biofilm. The pH in the hydroxyapatite group was around 0.5 units higher than the control groups. When acid attacks, hydroxyapatite releases calcium and acts as a buffer, reducing the acid's ability to demineralise the tooth surface at exactly the moment it matters most.

There is also a sensitivity mechanism. Exposed dentinal tubules are the microscopic channels in dentine that, when open, transmit sensations from hot, cold, and pressure to the nerve. Hydroxyapatite particles physically block those channels. A 2023 meta-analysis covering 44 clinical trials found that hydroxyapatite reduced dentin hypersensitivity by 39.5 percent compared to placebo, and outperformed fluoride by 23 percent in head-to-head comparisons.

Multiple in-situ studies have also shown that hydroxyapatite reduces initial bacterial colonisation on enamel surfaces, competing with bacteria for the tooth surface and reducing the attachment that allows plaque to form.

A: exposed dentine at gum recession. B: open dentinal tubules with nerve endings. C: SEM image of two open tubules. D: brushing HAP toothpaste onto surface. E: HAP layer after one application. F: tubules fully occluded after regular use, sensitivity resolved.

 Attribution: Limeback H, Enax J, Meyer F. Biomimetics 2023, 8(1), 23. doi:10.3390/biomimetics8010023

When we were building the Peg Paste formula, nano-hydroxyapatite was already the dominant form being marketed. Most of the oral care brands coming to market with hydroxyapatite were using it. It was positioned as the most advanced option.

We looked at it carefully. And the more we looked, the more questions we had.

Nano-hydroxyapatite does not exist in nature. It is engineered in a laboratory to shrink the mineral down to an ultra-small particle size, typically below 100 nanometres. Those ultra-small particles behave differently to larger ones. They carry more surface area per unit of volume, which is why they attracted research interest in the first place. But that same property, extreme smallness, is also what raises questions.

Nanoparticles do not always stay where you put them. They can interact with cells and tissues in ways that larger particles cannot. Some research has raised theoretical concerns about whether nanoparticles can cross biological barriers, be absorbed into tissues, or behave in unexpected ways over long-term daily exposure. The science is still active in this area. That alone gave us pause.

There is also a shape question that does not get discussed enough. Not all hydroxyapatite nanoparticles are the same shape. Rod-shaped particles within certain size ranges have been evaluated for safety. Needle-like particles have not been cleared, because early research suggested they may be more biologically reactive. Most products do not disclose the shape or surface treatment of the nanoparticles they use. You are largely taking it on trust.

We also had a simpler concern. People use toothpaste twice a day, every day. The mouth is one of the most absorbent surfaces in the body. In other areas of health and wellness, people scrutinise synthetic, lab-engineered ingredients carefully. Toothpaste often gets a pass. We did not think it should.

Microcrystalline hydroxyapatite particles are measured in micrometres, around 1,000 times larger than nanoparticles. They are not engineered to penetrate. They work at the surface of the enamel, physically adhering, depositing mineral, and buffering acid. That surface action is exactly what the three clinical trials above measured, and the results were non-inferior to fluoride across orthodontic patients, children, and adults over 18 months.

We chose micro because the clinical evidence was stronger in human trials, the ingredient stays closer to the form found in nature, and we were comfortable recommending it to people who use it every single day of their lives.

Micro-hydroxyapatite works at the surface of your enamel. It is the same mineral your teeth are made from, in a form that does not require engineering to an ultra-small particle size to do its job.