Hydroxyapatite

What it is

Hydroxyapatite is a mineral with the formula Ca₁₀(PO₄)₆(OH)₂. It's not just "similar" to enamel — it is the same material: tooth enamel is 96% hydroxyapatite crystals. Dentine is 70%.

When enamel breaks down under acid attack, it loses these crystals. Hydroxyapatite in toothpaste gives the body the same building material enamel is made from.

How it works

Remineralization happens in two stages:

1. Adsorption. Nanoparticles of HAp attach to the enamel surface and fill microcracks. At this level it provides physical protection: the surface becomes less porous.

2. Mineral exchange. In contact with saliva, HAp participates in ion exchange — supplying calcium and phosphate to demineralized zones. Enamel is rebuilt from within.

The key parameter is particle size. Nano-HAp (20–100 nm) penetrates micro-damage and intercrystalline spaces. Macro-particles do not.

Effectiveness

Clinical data compare nano-HAp with sodium fluoride at early-stage caries. Result: comparable remineralizing activity through a different mechanism.

HAp doesn't form fluorapatite — it works differently: it doesn't change enamel's chemical composition, it supplements it with the same material.

When it works: concentration above 10%, regular use (minimum 4 weeks), contact time at least 2 minutes.

When it doesn't: concentration below 3% — a decorative marketing ingredient. Most market pastes contain exactly that much.

Safety

Hydroxyapatite is a biocompatible material used in bone surgery and orthopaedics for decades. No data on systemic toxicity from toothpaste use. Safe for children — unlike high-concentration fluoride.

Not concentration-regulated (unlike fluoride, which has upper limits). Manufacturers can use any dose.

Comparison with fluoride

| Parameter | Hydroxyapatite | Sodium fluoride | |---|---|---| | Mechanism | Replenishes enamel material | Forms fluorapatite, more acid-resistant | | Child safety | No restrictions | Dose control under age 6 | | Working concentration | 10–15% | 0.15–0.32% (1000–2200 ppm) | | Evidence base | Growing since 2010s | Extensive since 1960s |

HAp and fluoride are not competitors. They are different protection mechanisms. An optimal formula can include both.