How much hydroxyapatite do you need? (5% vs 10%)

If you are shopping for hydroxyapatite toothpaste, the percentage on the label feels like the answer. 5% or 10%? More must be better—right?

Not necessarily. Dose-response data for HA are real, but they are not a straight “double the percent, double the benefit” line. Most of the strongest clinical caries trials used 10%. Some in-situ remineralisation work found 5% and 10% similar. Above about 10%, classic nano-HA systems often hit diminishing returns and formulation limits.

Common research and premium retail levels cluster at 5% and 10%. Some products disclose lower amounts; some do not disclose at all. Treat undisclosed percentage as a transparency gap when caries-trial alignment is part of your buying criteria.

What the percentages mean

The percentage usually refers to weight percent of hydroxyapatite in the finished paste. It does not, by itself, tell you:

• whether particles are nano or micro
• particle shape or coating
• how much HA actually contacts enamel during a two-minute brush
• what the rest of the formula does (abrasives, humectants, co-actives)

Two “10% HA” pastes can still behave differently.

Why labels feel inconsistent

Some brands print “10% hydroxyapatite” prominently. Others list hydroxyapatite deep in an ingredient deck without a percentage. A few talk about “nano” without dose. From a shopper’s perspective, that makes cross-brand comparison harder than it should be.

If caries-trial alignment matters to you, disclosed 10% is easier to relate to Schlagenhauf / Paszynska protocols than an undisclosed sprinkle of HA somewhere in the formula.

What laboratory dose-response shows

Huang et al. (2009) tested nano-HA concentrations from 1% to 15% in an in-vitro pH-cycling model of early enamel caries.

Finding in brief: remineralisation increased with concentration up to about 10%, and 10% was similar to 15%—a plateau. The authors suggested ~10% may be near-optimal in that model.

That is laboratory evidence on artificial lesions. Useful for formulation, not a clinical ranking of commercial pastes.

What a plateau implies for shoppers

A plateau means extra mineral in the tube may not translate to extra mineral benefit on the tooth once a threshold is reached—especially if particles aggregate or if contact time is short. Paying for 15% because it sounds stronger than 10% is not strongly supported by that in-vitro curve.

What in-situ work shows for 5% vs 10%

Najibfard et al. (2011) studied early caries remineralisation in situ with nano-HA dentifrices at 5% and 10%, compared with each other and with an 1,100 ppm fluoride dentifrice.

Finding in brief: both 5% and 10% nHA remineralised early lesions; there was no significant difference between 5% and 10% (or versus the fluoride control) for percent mineral gain in that protocol.

So if your mental model is “5% is half as good,” this study does not support it—at least for short-term mineral gain with nano-HA.

Why in-situ and clinical answers can diverge

In-situ models measure mineral change in enamel specimens under real oral conditions for a limited time. Clinical caries trials count new lesions or DMFS changes over months to years in whole mouths with diet, plaque, and behaviour in the mix.

A dose that looks similar for short-term mineral gain can still differ—or simply remain untested—for long-term cavity endpoints. That is why this guide refuses to say “5% equals 10% for cavity prevention.” The honest line is: 5% has supportive remineralisation data; 10% has the caries RCT track record.

What clinical caries trials used

The modern non-inferiority caries RCTs that readers cite most often used 10% microcrystalline HA:

• Schlagenhauf et al., 2019 — orthodontic patients, ~6 months.
• Paszynska et al., 2021 — children aged 3–7, ~1 year.
• Paszynska et al., 2023 — adults, 18 months.

Those trials are why 10% is the best-studied clinical concentration for HA caries endpoints. They are not a randomised proof that 5% fails those same endpoints—5% simply was not the dose those protocols tested.

Anil et al. (2022) scoping review notes 10% as the most common level in RCTs and flags practical problems with very high loadings (aggregation) above roughly 15% in conventional systems.

For trial results and limits (industry funding, non-inferiority margins), see hydroxyapatite and cavity prevention and the fluoride comparison.

Remineralisation studies vs caries trials

It helps to separate two questions:

1. Can this dose support mineral gain in early lesions? Najibfard’s in-situ work says yes for both 5% and 10% nHA in that protocol.
2. Has this dose been tested for clinical caries endpoints against fluoride? The published non-inferiority RCTs point to 10% microcrystalline HA.

People shopping only for smoother feel / sensitivity comfort may weigh (1) more heavily. People choosing fluoride-free paste primarily for cavity anxiety should care more about (2)—while still remembering fluoride’s larger evidence base.

If a brand cites Huang 2009 to sell 15% as better than 10%, remember the same paper’s plateau: more was not meaningfully better in that model past about 10%.

Safety ceilings are not the same as “best dose”

EU scientific opinions on nano-HA set concentration ceilings for specified morphologies (historically up to 10% in toothpaste under SCCS/1648/22 and Regulation 2024/858; Submission IV in 2025 supported higher scientific ceilings for characterised materials). Those numbers answer “how much is considered safe for this nano grade,” not “how much maximises cavity prevention.”

Microcrystalline HA is not the same regulatory entry as nano-HA. Do not mix safety caps with efficacy targets.

A paste can be below a safety ceiling and still be under-dosed relative to clinical trials—or disclosed at 10% and still use a particle grade that differs from the trial grade. Concentration is necessary context, not sufficient proof.

When higher percentages are not comparable

Some European zinc-carbonate HA / “microRepair” style products report mineral loadings that look much higher than 10% on paper. Those systems differ in substitution chemistry and labelling conventions. A headline percentage from a ZnCHA paste is not automatically “3× better” than a 10% stoichiometric HA paste.

One materials analysis discussed in the secondary literature has cited roughly 31.7 wt% zinc-substituted HA in a Biorepair-type system—useful as a reminder that label math differs across technologies, not as a ranking score.

Compare like with like: chemistry, particle grade, and clinical citations—not the biggest number on the box.

Practical buying guidance

Does nano change the percentage you need?

Possibly in theory—smaller particles have higher surface area per gram—but clinical head-to-head proof that nano lets you use a lower percentage for equal caries outcomes is not established. Najibfard’s in-situ work used nano-HA at both 5% and 10% with similar mineral gain. The major caries non-inferiority trials used 10% microcrystalline HA.

So “we use nano, so 3% is enough” is a hypothesis until someone publishes the matching clinical programme.

A simple decision rule

1. Prefer brands that disclose concentration.
2. Treat 10% as the concentration with the clearest caries-trial alignment.
3. Treat 5% as a dose with supportive remineralisation data—not as “weak by definition.”
4. Be sceptical of “20% must be twice as good as 10%” marketing.
5. Weigh the rest of the formula: abrasivity, flavour oils, xylitol/zinc, and whether nano/micro claims are characterised.
6. If the brand will not state a percentage, ask why—or choose a more transparent option.

Habits that matter as much as percent

Concentration cannot rescue a thirty-second brush. Contact time, spit-don’t-over-rinse habits, sugar frequency, and dry mouth all influence whether any remineralising paste gets a fair chance. For routine tips, see how to use hydroxyapatite toothpaste.

For a fuller checklist, use the buyer’s guide. Mechanism context sits in Does hydroxyapatite remineralise teeth?.

Where Klyyr sits on dose

Disclosure: This website is operated by Klyyr, which sells hydroxyapatite toothpaste.

Klyyr One+ is a fluoride-free mint toothpaste with 10% hydroxyapatite (nano + micro blend). That dose matches the concentration used in the major caries non-inferiority trials discussed above. Particle morphology for the nano fraction (aspect ratio, coating, full size distribution) is not published here, so we do not claim EU SCCS rod-shaped compliance for that fraction.

Choosing 10% because it matches trial doses is a transparency argument. It is not a claim that Klyyr’s specific blend has been the test product in those RCTs—those trials used other commercial microcrystalline systems—or that any 10% paste is interchangeable.

Bottom line

You do not need an escalating HA percentage arms race.

5% can be meaningful in remineralisation models. 10% is the clinical caries-trial workhorse and sits near an in-vitro plateau for nano-HA. More than 10% is not automatically better for classic HA systems.

Buy for disclosed dose, honest citations, and fit to your goals—not for the largest integer on the label. If two pastes both disclose 10%, read particle claims and the rest of the formula before treating them as equals.