What percentage of nano-hydroxyapatite does a toothpaste need? What the studies used.

The concentrations that have been tested in people run from 5% to 15%, and no trial has established that one figure inside that range does more than another. Six studies have compared one concentration of hydroxyapatite against another — two in situ in real mouths, one an industry-funded randomised clinical trial, three in vitro — and four of the six found no difference at all; the two that did found it in a laboratory below ten per cent, and at a single timepoint in one trial²³⁴⁵⁶⁷. So the useful answer is a range rather than a number, and anyone who tells you that ten per cent is the threshold is repeating something no clinical trial has measured. S3 Sensitivity Science™ uses 10% nano-hydroxyapatite and 5% biomimetic hydroxyapatite, both stated as inclusion levels of the ingredients as supplied.

What was checked16 peer-reviewed studies, product information as published by each brand

What percentage of hydroxyapatite does a toothpaste need?

Enough to be somewhere inside the range that has been tested, which is the most a reader can honestly be told today. The question feels as though it should have a number attached, because the neighbouring questions do: fluoride comes at 1450 ppm because a dose–response for fluoride has been designed for and measured, most recently in a 28-day laboratory model on 187 bovine dentine specimens where mineral loss tracked the fluoride concentration across nought, 500 and 1100 ppm in vitro¹³. Potassium compounds are the most-tested desensitising actives of all: a systematic review of 138 randomised trials counted them in 68 of the 368 toothpaste formulations it catalogued⁸. Hydroxyapatite has no equivalent behind it.

That is not a criticism of the ingredient, and it is not an argument that the percentage is meaningless. It is a statement about how much work has been done. In that systematic review's catalogue of 368 formulations, hydroxyapatite is the active in nine⁸. The work behind those nine was never built to look for a dose, and where two concentrations have turned up in one piece of it, they have almost always behaved the same.

What concentrations have the studies actually used?

Five, ten and fifteen per cent, with a laboratory tail either side. The cleanest clinical result sits at 15%: in a four-week double-blind randomised trial of 105 adults, a fluoride-free 15% nano-hydroxyapatite toothpaste reduced cold-air and tactile sensitivity more than a fluoride toothpaste and a placebo at two and four weeks¹. The longest sits at 10% and 15% together: an eight-week double-blind randomised trial sponsored by the maker of the test pastes, with 85 adults completing across four arms, in which 10% and 15% nano-hydroxyapatite, with or without potassium nitrate, were as effective as a calcium sodium phosphosilicate toothpaste².

The laboratory work fills in around them. Under an electron microscope, a 15% nano-hydroxyapatite toothpaste occluded about 98% of dentinal tubules in vitro, against about 83% for a calcium sodium phosphosilicate paste and about 69% for an arginine paste, and the gap between the first two was not statistically significant¹⁴. A second in vitro study brushed a 15% paste onto human dentine blocks daily for a fortnight and recorded 66.13% of tubules occluded, ahead of two commercial desensitising pastes and level with a third; the test material was donated by the company that makes it¹⁵. At the bottom of the laboratory range, a 7% nano-hydroxyapatite toothpaste put more mineral back into bovine dentine lesions in vitro than an amine fluoride paste did¹⁶. Lower again, an in vitro study of 24 extracted human teeth built gels at 2.5% and 5% with potassium nitrate and measured surface hardness recovery over seven days⁷.

Nothing clinical exists below 5% or above 15% in a toothpaste used by brushing. That boundary is the honest edge of the recommendation, and it is worth more than a single figure inside it.

Has anyone compared one concentration against another?

Six times since 2009, and four of those six found nothing at all. Here they are in one place, with the model each used and the result each reported.

Read down the result column and the pattern is hard to miss. One study found a gradient, in a laboratory, on cow teeth, and it found it below ten per cent rather than above³. One trial, sponsored by the manufacturer of the pastes, found a single difference out of eight comparisons, at one timepoint, on one stimulus². Everything else is flat. Doubling the mineral from 5% to 10% changed nothing measurable in situ in 30 adults wearing appliances for 28 days a phase⁴. Doubling it again from 10% to 20% changed nothing in vitro either, in a model where neither concentration beat leaving the specimen alone⁵. The 10% and the 15% pastes were indistinguishable on four separate occlusion measures in situ in 80 participants⁶. And 2.5% and 5% were indistinguishable in vitro on 24 extracted human teeth⁷.

One more study is worth naming, with its limits. In vitro, on 160 bovine enamel blocks over 14 days of pH cycling, eight marketed toothpastes were put on one bench by a group whose lead author reports being funded by a commercial sponsor¹². Every product raised surface microhardness significantly in that industry-funded work, and the one product to separate from any other was Fygg, which declares the highest hydroxyapatite content in the set and came out ahead of Boka, RiseWell Regular and one further product declaring 10%¹². That is the closest thing to a shelf-wide ranking anyone has published, and it is not a concentration comparison: those eight products differ in particle type, base, abrasive and fluoride as well as in percentage, so a gap between two of them is not a gap between two numbers. The result says as much itself, since in the same industry-funded run in vitro a 5% product and a 15% product both sat level with the 20% one¹².

Where does "ten per cent is the optimal concentration" come from?

From one laboratory study on cow teeth, published in 2009, which said "may be optimal" and meant something narrower than the internet has made of it³. Four sources are usually behind the claim. Two of them are a Spanish-language postgraduate thesis and an Indian master's dissertation; neither is indexed anywhere that vets editorial standards, and under this site's method a thesis is never a published study, so neither can be cited here.

The other two are real, peer-reviewed and MEDLINE-indexed, and both were resolved for this page. The first is the source of the phrase: an in vitro study that cycled bovine enamel lesions through acid and saliva for 12 days with nano-hydroxyapatite at 1%, 5%, 10% and 15%, alongside sodium fluoride and water controls³. Surface microhardness recovery climbed as the concentration climbed, up to 10%, and then stopped climbing; the 10% and 15% groups did not differ significantly at any measurement point, and the authors concluded that 10% "may be optimal" for early enamel caries³. That is a plateau, not a peak. It describes where a curve flattens in one bench model, on an animal substrate, measuring enamel hardness in vitro rather than dentine hypersensitivity in a person³. No trial in a mouth has put the question since.

The second is a negative study that almost nobody quotes: experimental pastes at 10% and 20%, with and without fluoride, on bovine enamel and root dentine, in which neither concentration reduced subsurface hardness loss any more than no treatment at all, while a 0.2% sodium fluoride paste did⁵. It belongs on this page for the same reason the first one does. Between them they are the published foundation of "ten per cent", and what they actually show is a flattening curve in one model and no effect at all in another.

Why the number on so many tubes is ten rather than anything else is a separate question — supply form, research habit and a safety ceiling all push the same way — and the page on why that concentration keeps appearing takes it up. Ten per cent as supplied is also what S3 prints, which is why this page says all of that rather than none of it.

Why do the meta-analyses not settle it?

Because none of them separates its results by concentration, and they say so. A 2019 systematic review and meta-analysis of six four-week randomised trials found nano-hydroxyapatite relieved dentine hypersensitivity better than its comparators on evaporative and tactile stimuli, pooling every concentration together⁹. A 2023 systematic review and meta-analysis of 44 clinical trials, whose authors include scientists employed by Dr Wolff, a maker of hydroxyapatite toothpastes, found hydroxyapatite products cut dentine hypersensitivity by 39.5% against placebo and gave 23% greater relief than fluoride toothpastes, again with every form and level pooled¹⁰. A 2024 systematic review and meta-analysis of white spot lesions, whose evidence is mostly laboratory, reports a mineral effect and a null result on appearance without splitting by percentage either¹¹.

That is not sloppiness on their part. You cannot pool by a variable the underlying trials did not vary. A systematic review of 138 randomised trials of desensitising toothpaste catalogued 368 formulations and found hydroxyapatite as the active in nine of them⁸. Nine formulations, spread across nearly six decades of trials and several different hydroxyapatites, is not enough to build a dose–response from, however the numbers are arranged afterwards.

What do the tubes on the UK shelf actually declare?

Four of them declare a hydroxyapatite concentration, and thirteen do not. This page compares ingredients and stated actions only, not clinical performance, based on what each brand states about its own formula. Prices and formulations may change; always check the pack.

Of the 17 hydroxyapatite toothpastes with a full ingredient list in this site's UK scan, four state a hydroxyapatite concentration and thirteen state nothing at all. The Fygg row is marked pending because the brand does not publish a full ingredient list, and it is printed anyway because its wording is the clearest demonstration on the shelf of what a percentage can hide: twenty per cent of a raw material, and about three per cent of mineral in the tube. The full scan, with every row and its source, is the category review of UK sensitivity toothpastes by ingredient, and the page on reading a hydroxyapatite label correctly explains what each form of the number refers to.

What does S3 use, and why state it that way?

10% nano-hydroxyapatite and 5% biomimetic hydroxyapatite, given as inclusion levels of the ingredients as supplied, with the active hydroxyapatite content lower and both figures stated. The levels were chosen to match the concentrations the published studies used, alongside 5% potassium nitrate. Neither of those is a claim that ten per cent is the right number. It is a claim about which shelf of the literature the formula was built on, and about which of two possible meanings the figure on the tube carries.

The distinction matters more than it sounds. A trial arm described as "10% nano-hydroxyapatite" and a tube described the same way can hold different amounts of mineral, because the raw material often reaches a formulator as a water-based paste and the percentage may count either the ingredient as supplied or the mineral inside it. Every study in the table above states its concentration in its own terms, and their abstracts almost never say whether the figure counts the mineral or the material it arrived in. That is the single largest obstacle to adding this literature up, and it is the reason a page like this ends in a range rather than a recommendation.

What can a percentage not tell you?

Four things, each of which can matter as much as the number.

Particle size and shape. The nano-hydroxyapatite in S3 is under 100 nm, rod-shaped and crystalline, while the biomimetic hydroxyapatite beside it is around two microns and less crystalline; one is sized to enter a dentine tubule, the other to sit on the surface. Two tubes printing the same figure can carry crystals with different dimensions and different destinations, and the page on why particle size decides what hydroxyapatite can do takes that argument further.

What the mineral is mixed with. The abrasive, the base and the surfactant decide how much of the mineral survives brushing and how much reaches the tooth. On the one bench where eight marketed hydroxyapatite toothpastes were compared in vitro, in work funded by a commercial sponsor, the ranking did not follow the declared percentages¹².

Whether there is a second mechanism in the tube. Occluding a tubule and quieting the nerve inside it are different jobs, and hydroxyapatite does one of them. The 8-week trial that ran a plain 10% paste against the same paste with 5% potassium nitrate, sponsored by the maker of both, is the study to read on that question².

Whether fluoride is still there. Four of the five products with a declared hydroxyapatite figure in the table above carry no fluoride at all, and giving up decay protection to gain mineral is a trade a reader should make deliberately rather than by accident. The Sensitivity Journal walks through that decision in its guide to choosing a toothpaste when your teeth are sensitive.

Frequently asked questions

Is 15% better than 10%?

Not on the evidence. Three pieces of work have put those two figures side by side. In situ, on dentine blocks worn by 80 participants, they were indistinguishable on all four occlusion measures at seven and 14 days⁶. In vitro, on bovine enamel, the 10% and 15% groups did not differ at any measurement point across 12 days of pH cycling³. In the one randomised trial that ran both, sponsored by the maker of the pastes, they differed at a single point out of eight comparisons, on the cold stimulus at week six, and matched everywhere else². One difference at one timepoint, in work not built to look for a dose, is not a dose–response.

Is S3's 10% better than another brand's 15%?

Nothing published supports that comparison, and the two figures may not even be measured on the same thing. One brand may be counting the supplied raw material and another the mineral inside it, and neither is obliged to say which. Where a genuine head-to-head has been run in situ between 10% and 15% of the same material, in the same base, in the same mouths, the answer has been no difference⁶.

Is there a minimum below which hydroxyapatite does nothing?

Nobody has found one. The lowest concentrations anyone has tested — 1% and 2.5% — both produced measurable changes in the laboratory: 1% recovered less enamel surface microhardness than 10% but more than the untreated control in vitro³, and 2.5% matched 5% for hardness recovery on extracted human teeth in vitro⁷. Those are bench results on enamel and dentine specimens, not anything a person noticed. The lowest concentration ever carried into a human study is the 5% worn in situ on appliances by 30 adults, and no toothpaste below that has been tried on anybody⁴. Below that, there is nothing to report either way.

Does a percentage on the front of the tube mean the same thing on every brand?

No, and the shelf makes that plain. One brand in the table above states 20% of a raw material and about 3% of mineral per tube in the same sentence, which are both true and describe one product. Another states 12% and splits it elsewhere into 7% nano plus 5% micro. Without the basis attached, two figures cannot be lined up, and most hydroxyapatite toothpastes in this site's UK scan publish no figure at all.