Using hydroxyapatite toothpaste but still getting sensitivity? Six things to check.

A hydroxyapatite toothpaste that still leaves you sensitive has usually hit one of six limits the published evidence already describes: it is too early to judge, your trigger is cold, the tube carries no nerve active, something keeps stripping the surface, the percentage on the label is being read as a dose, or the pain is not dentine sensitivity at all. Only two of those six, the cold trigger and the missing nerve active, are things a different tube can change, and the first of those only partly. S3 Sensitivity Science™ is a hydroxyapatite toothpaste that also carries 5% potassium nitrate for the nerve and keeps 1450 ppm fluoride; whether that matters for you depends on which of the six checks below your problem fails.

What was checked18 peer-reviewed studies, product information as published by each brand, and guidance from the NHS and the Oral Health Foundation

Have you given it as long as the trials did?

Not if you are under four weeks. The pooled evidence on nano-hydroxyapatite and sensitivity comes from trials that ran for four weeks¹. The double-blind trial of 105 adults that set a fluoride-free 15% paste against a fluoride paste and a placebo took its readings at two weeks and at four³. A 2026 systematic review of 31 randomised trials of newer desensitising treatments records most of its included studies stopping somewhere between four and six weeks⁴. So a month of brushing morning and night gives your paste the same run the trial pastes had. A verdict on day ten is a guess.

Write down the date you opened the tube. If you are past four weeks and nothing has moved, carry on down this list; if you are not, the most useful thing to change is nothing. Every reading day in every trial is laid out on the page on how long nano-hydroxyapatite toothpaste takes to work.

Is cold your trigger?

Then you are the reader the hydroxyapatite evidence helps least. When a 2019 meta-analysis of six four-week randomised trials split its results by stimulus, nano-hydroxyapatite came out ahead of its comparators on a blast of air and on a dental probe, and level with them on cold¹. S3's hydroxyapatite belongs to that same class of ingredient, and this page makes no claim that it escapes the result on cold.

The largest synthesis so far changes that less than it appears to. The 2026 network meta-analysis of 93 randomised trials gives nano-hydroxyapatite a large two-week effect, but the measure is the Schiff score after a jet of cold air, the estimate rests on two studies, and it is rated moderate confidence⁵. A blast of air from a dental syringe and a mouthful of iced water are different stimuli, and the page on what happens inside a dentine tubule when you drink something cold explains why a result on one is not automatically a result on the other. The toothpaste active with the best-supported two-week result in that same network is stannous fluoride, rated high confidence on the cold-air score where hydroxyapatite is rated moderate, and S3 does not contain it⁵. Every review on the ingredient is set side by side on the page on whether nano-hydroxyapatite toothpaste works for sensitive teeth.

We looked for more. A PubMed search run for this page on the tenth of September 2026, for hydroxyapatite toothpaste trials that used cold water, iced water or another thermal stimulus, returned eight records, and every randomised trial among them with a hydroxyapatite arm was already in this site's study library⁶⁷⁸⁹. The table lists them with one more from the library: an eight-week randomised trial, sponsored by the maker of its test pastes, that used ice-cold water¹⁰.

In the four trials that set a paste relying on hydroxyapatite alone against another active paste and reported cold water separately, hydroxyapatite was never the best on that stimulus: level in two, second of three in another, and in the fourth, sponsored by the maker of the test pastes, the plain 10% paste fell behind at weeks six and eight⁶⁷⁸¹⁰. None of that says hydroxyapatite does nothing to cold. It says the edge it shows on air has not turned up on iced water.

If cold is your trigger and four weeks have gone by, buying another hydroxyapatite paste is not a move the evidence backs. What it leaves open is an active that works on the nerve side, which the next two sections take up, and stannous fluoride, the active with the strongest cold-air result in the 2026 network meta-analysis⁵. If the cold pain sits in one tooth, go straight to the last check. The Journal's guide to teeth sensitive to cold covers the everyday side of this trigger.

Does your paste carry a nerve active, and does it keep fluoride?

Probably neither, if it is one of the hydroxyapatite pastes on the UK shelf. This site's category review of UK sensitivity toothpastes by ingredient recorded the published ingredient lists of 17 toothpastes containing hydroxyapatite in any form, read from brand and retailer pages on the ninth of September 2026. Six of the 17 list potassium nitrate, potassium chloride or potassium citrate, four list a fluoride salt, and two list both. Counted the other way, eleven of the 16 hydroxyapatite pastes that are not S3 carry none of those three potassium salts, thirteen of the 16 carry no fluoride, and nine carry neither.

The two gaps mean different things. Hydroxyapatite's work in a sensitivity paste is at the tubule, closing the open channels that carry a cold or sweet stimulus inwards, while potassium's is at the nerve, and neither can do the other's part. A paste with no potassium salt has left that second part alone.

Fluoride is a separate question from sensitivity. The NHS advice is to brush twice a day with fluoride toothpaste¹¹. A fluoride-free paste is not unsafe, and nothing here says it is; what it leaves out is the decay protection that advice is built on. If yours is one of the thirteen without it, the guide to toothpaste with both fluoride and hydroxyapatite covers the pastes that keep both.

The table sets the shelf out by what else is in the tube, as each brand or retailer publishes it. 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. Three rows are given by product type rather than brand name, because the scan did not establish that those products are sold in the UK. Only potassium nitrate, chloride and citrate are counted in the potassium column; a potassium pyrophosphate or sorbate elsewhere in a list is not. Prices are as shown when each page was read, and S3's is taken from its own product page.

† The Spotlight price is printed as the category review recorded it on the ninth of September, from a Boots listing that was not saved, so it could not be matched to a saved page this morning.

Read the potassium and fluoride columns together and the shelf falls into three groups: nine pastes with hydroxyapatite and neither of the two, six with one of them, and two with both.

If your paste has no nerve active, what does adding one change, and where does S3 fit?

One randomised trial has tested exactly that change, and the company that made the pastes paid for it. In an eight-week double-blind trial of 85 adults, sponsored by the maker of the test pastes, the group whose 10% nano-hydroxyapatite paste also carried 5% potassium nitrate reported less pain to ice-cold water than the group using the same paste without it at weeks two, four and six, was no longer ahead at week eight, and reported less pain to an air blast at weeks four, six and eight¹⁰. The company that sponsored it is also the maker of the Apagard paste in the table above, so the funder of that trial sells hydroxyapatite toothpaste on the shelf this page lists¹⁰.

That is half the question. The manufacturer-sponsored trial set the pairing against hydroxyapatite alone and never against potassium nitrate alone, and every group, the plain pastes included, improved from its own starting point¹⁰. The pooled figure most often quoted for potassium plus hydroxyapatite comes from a node of a 2020 network meta-analysis built on two randomised trials and 140 patients, and that network holds no potassium-plus-hydroxyapatite result for cold at all¹². Dropping hydroxyapatite for a different desensitiser altogether is a sideways step on the pooled evidence: 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 level with other desensitising agents, not ahead of them¹³. The page on potassium nitrate and hydroxyapatite together works through what that pooled figure can and cannot carry.

S3 puts both halves in one tube: potassium nitrate for the nerve, nano-hydroxyapatite working inside the tubule and biomimetic hydroxyapatite on the surface, each doing a job the other two cannot. Unlike a fluoride-free hydroxyapatite paste, S3 does not ask you to give up decay protection, because it keeps full adult-strength fluoride, 1450 ppm as sodium monofluorophosphate. The Journal's piece on the two causes of sensitive teeth explains the nerve-and-tubule idea for a first-time reader.

The limits come with it. No controlled trial has tested potassium nitrate, hydroxyapatite and fluoride together in one finished toothpaste, S3's formula included. The case for adding the nerve half rests on mechanism and on that one sponsored trial, not on a result anyone has measured for S3. And if what your current paste lacks is fluoride and not a nerve active, you do not need S3 to fix it. Georganics lists hydroxyapatite with 1350 ppm sodium fluoride, at £4.90 on its own site when the table was read, a fraction of S3's price.

What keeps stripping the surface?

Acid, abrasion, and a layer nobody has timed. A hydroxyapatite paste leaves mineral in and over the open tubules, as the page on how nano-hydroxyapatite seals dentine tubules shows step by step, and anything that takes mineral off the surface reopens the route it was covering. Two of those three are about what happens to your teeth between one brushing and the next, and the third is a hole in the evidence.

Acid is the one that has been looked at in people. In a cross-sectional clinical study of 350 adults aged 19 to 34 in south-east England, the more recently someone had eaten or drunk something acidic, the more severe their air-blast sensitivity on the biting surfaces tended to be¹⁴. A snapshot taken at one appointment cannot say which came first, and that study measured the biting edges of the teeth, not the necks where receding gums expose root¹⁴. The Oral Health Foundation lists acid wear from fizzy drinks, fruit juice, citrus fruit and stomach acid among the causes of sensitive teeth, and suggests cutting down on acidic drinks and waiting at least an hour after them before brushing¹⁵. The waiting half of that advice stands on less than it sounds: pooling twelve laboratory and in situ studies, a 2020 meta-analysis could not separate brushing straight after an acid attack from waiting, for human enamel, and had no human dentine study to pool¹⁶. The page on acidic food and drink triggers goes through the drinks and the timing, and the Journal's explainer on tooth enamel erosion covers the wear itself.

Abrasion is the one people ask about, and one trial has isolated it¹⁷. In a double-blind randomised trial of 40 adults with sensitivity at the necks of their teeth, two strontium chloride toothpastes identical apart from their abrasive systems were used for eight weeks, and relief did not differ between them at any reading¹⁷. Wear is a different outcome from pain. In a randomised in situ study of 28 volunteers wearing appliances that held slices of dentine, a paste with a relative dentine abrasivity of 70 wore the slices significantly less than one rated 120 over fifteen days, with or without an acid rinse first, and the extra wear the acid added did not depend on the paste¹⁸. It scored wear, not anyone's sensitivity¹⁸. An older in situ study of four people found brushing with an abrasive paste left most dentine tubules open where brushing with no paste let a saliva-derived deposit close them, again with no pain score, and it is not advice to brush without toothpaste¹⁹. S3 publishes no abrasivity figure, so this page cannot place it on that scale.

How hard you brush, and with what, is the other side of abrasion. The Oral Health Foundation's advice is a soft toothbrush and gentle, small circular movements, on a page supported by an educational grant from a toothbrush company¹⁵, and the page on sensitivity getting worse despite a sensitive toothpaste covers force and bristles in detail. Rinsing and mouthwash sit in the same check: the Oral Health Foundation says to spit after brushing and not rinse with water¹⁵, nobody has measured whether either habit changes what a hydroxyapatite paste does for sensitivity, and the page on rinsing, mouthwash and timing after brushing sets out what has been measured instead.

Then there is the gap. Nobody has measured how long a hydroxyapatite layer left by a toothpaste survives a normal day of eating, drinking and brushing, and that includes the layer S3's biomimetic hydroxyapatite leaves on the surface. The page on how nano-hydroxyapatite crystals sit on enamel follows the few hours anyone has watched. Over months, a 2025 systematic review of 22 randomised trials with at least six months of follow-up found that the calcium-phosphate desensitisers, the class hydroxyapatite belongs to, did not reach statistical significance, while several other agents did². What the evidence describes is a routine, not a shield: the mineral goes on at each brushing, and nothing measured says it stays.

Is the percentage on your tube telling you what you think?

Rarely, because most tubes print no percentage, and where one is printed it may not count the mineral. Four of the 17 hydroxyapatite ingredient lists in the table come with a printed level. One gives the mineral in the finished paste. S3's figures of 10% nano-hydroxyapatite and 5% biomimetic hydroxyapatite describe the ingredients as supplied, at their inclusion levels, and the active hydroxyapatite inside is a lower amount. So a big number on one tube and a small one on another may not be measuring the same thing, and the page on reading a nano-hydroxyapatite label walks through what each kind of figure counts. Concentration itself gets its own page on what percentage of nano-hydroxyapatite a toothpaste needs.

Could it be something other than sensitivity?

Sometimes, and no tube can check that for you. The trials behind every hydroxyapatite result on this page set out to enrol people whose pain came from exposed dentine, yet a 2026 scoping review and consensus exercise found that few trials apply every part of the accepted definition, least of all the part that rules out other causes of tooth pain²⁰. No symptom pattern you can notice at home has been shown to tell dentine sensitivity apart from a cracked tooth or an inflamed nerve, which is why the next step here is an examination and not another paste.

The Oral Health Foundation gives four reasons to book a dentist instead of carrying on brushing: the pain is severe, it has lasted more than a few weeks, it is in one tooth, or it came on suddenly, and it names decay, a crack, gum problems and infection as what those signs can mean¹⁵. The NHS draws its line for toothache at more than two days, or pain that painkillers do not ease, or pain that comes with a high temperature, pain when you bite, red gums, a bad taste or a swollen cheek or jaw²¹. If your sensitivity sits in a single tooth, the page on why one-tooth pain usually needs a dentist explains why a whole-mouth toothpaste is the wrong test for it.

What should you try, in order?

Nobody has published a description of the people a hydroxyapatite toothpaste leaves sensitive: a PubMed search for non-responders, treatment failure or persistent sensitivity with hydroxyapatite, run for this page on the tenth of September 2026, returned two records, and neither was about them. So the order below is built from what the evidence behind each limit can tell you, not from a trial of troubleshooting. Work down the checks and stop at the first one that fits. The last column answers the question most people are really asking, which is whether a new tube is the fix.

Frequently asked questions

Should I switch from my hydroxyapatite toothpaste to S3?

Only if check three is where your paste falls short: it has no nerve active, or it has no fluoride and you want it back. S3 adds 5% potassium nitrate and keeps 1450 ppm fluoride beside its two forms of hydroxyapatite. Its hydroxyapatite is the same class of ingredient as the one in your current tube, though, so a cold trigger, acid and abrasion, a percentage read as a dose and a tooth that needs a dentist all come with you after the switch. If fluoride is all that is missing, a hydroxyapatite paste that keeps it for less money is in the table.

Does hydroxyapatite help cold sensitivity?

Less than it helps with air and touch, on the evidence so far. The meta-analysis of six four-week randomised trials that broke its results down by stimulus had nano-hydroxyapatite ahead on air and on a probe, and level with its comparators on cold¹. The 2026 network's large hydroxyapatite estimate is a cold-air score from two studies at moderate confidence, which is not the same test as a cold drink⁵. And the randomised trials that did use cold water, one of them sponsored by the maker of the pastes, never put a hydroxyapatite paste first⁶⁷⁸¹⁰.

Is a higher percentage of hydroxyapatite stronger?

Nobody has shown that it is. In the one randomised trial that put two strengths into the same base, sponsored by the company that made both pastes, 15% and 10% nano-hydroxyapatite differed at a single one of eight comparisons, on cold at week six, and never on air¹⁰. Concentration is weighed in depth on the page on what percentage of nano-hydroxyapatite a toothpaste needs.

Should I go back to a fluoride toothpaste?

The NHS advice is to brush twice a day with a fluoride toothpaste¹¹. A hydroxyapatite paste without fluoride is not unsafe; it leaves out the decay protection that advice relies on. Going back to fluoride does not mean giving up hydroxyapatite: four of the 17 hydroxyapatite lists in the table include a fluoride salt, and S3 keeps full adult-strength fluoride, 1450 ppm as sodium monofluorophosphate.

Can I use a hydroxyapatite paste and a potassium paste together?

Nobody has published a trial in which one person used two desensitising toothpastes with different actives, together or in turns, so nobody can tell you whether it adds anything. What it can cost you is a fluoride brushing, if one of the two has none; the page on using two sensitivity toothpastes together goes through the options.