Using it only when it hurts: what stop-start use does to a sensitivity toothpaste.
Using a sensitivity toothpaste only when it hurts does not throw the benefit away, but it does keep you in the part of the timetable where the evidence for any paste is weakest. In an industry-funded trial most of the gain from eight weeks of brushing with a potassium nitrate paste was still there three weeks after people stopped, in an older trial whose record names no funder sensitivity had crept back only slightly twelve weeks after a strontium paste was put down, and every restart begins again with the slow first fortnight, which is exactly when a paste is easiest to write off12. S3 Sensitivity Science™ is designed as the toothpaste you use every day rather than a fortnight's treatment, and the one trial that compared stop-start with daily use found no difference between them, which is worth knowing before you choose any paste on that basis.
What was checked13 peer-reviewed studies, product information as published by each brand, and Oral Health Foundation guidance
- Three weeks after an eight-week course of a potassium nitrate paste ended, the group in a double-blind randomised trial funded by Procter & Gamble still held about four fifths of its cold-air advantage over a plain paste, and a randomised follow-up whose record names no funder found sensitivity only slightly back twelve weeks after people stopped a strontium paste12.
- The only trial of on-and-off use, sponsored by GSK Consumer Healthcare, gave adults a bioactive-glass paste either every day for twenty-four weeks or in two eight-week courses with eight weeks on an ordinary paste between, and the two schedules finished level with small gains on cold air; the consensus guidelines for these trials ask for eight weeks of use before a paste is judged34.
- Single applications in a clinic reduced sensitivity immediately afterwards in trials of arginine, strontium acetate and stannous fluoride, every one of them run with the manufacturer, but none used potassium nitrate as the paste being tested, and a systematic review of 74 randomised trials puts potassium nitrate only among the treatments whose effect shows over the long term5678.
- S3's own wording judges it at two to four weeks, and restarting any paste, S3 included, starts that clock from the beginning again.
- Nobody has put a potassium nitrate toothpaste used only on bad days to the test: searches of PubMed for this page on the tenth of September 2026 turned up no record of it.
What happens to the benefit when you stop?
Most of it stays for weeks, and what goes, goes gradually.
The clearest measurement is a washout arm in a double-blind randomised trial of 120 adults funded by Procter & Gamble: after eight weeks the potassium nitrate group's advantage over a plain fluoride paste on the cold-air test was 44.3%, and after three more weeks on that plain paste it was still 35.8%1. The page on what happens when you stop using a potassium nitrate toothpaste goes through that washout visit by visit.
A second active, and a second era, point the same way. In 1992, 40 adults who had brushed with one of two strontium chloride pastes under supervision for eight weeks were examined again twelve weeks after they stopped, in a follow-up of a randomised trial whose record names no funder, and sensitivity had drifted back slightly in both groups while staying significantly below where it began2. That follow-up had no placebo group, so some of what held may owe nothing to the strontium.
At the short end, a double-blind randomised trial of 127 adults, whose authors are employees of the Lion Corporation that makes the pastes or hold its research grants, built a day off into its schedule: after four weeks everyone brushed with a placebo paste for a day, the 5% potassium nitrate group came back no worse, and the placebo group's own readings drifted the same way over the same twenty-four hours9. What a missed week on potassium might cost, bracketed by those trials, is set out on the page on missing a week of a potassium nitrate toothpaste.
None of this reaches very far. Twelve weeks off a strontium paste is the longest gap this page found anyone measuring, three weeks is the longest for potassium nitrate, and nobody has followed people who stop and start again and again over a year. The guidance is written without those measurements. The Oral Health Foundation says of sensitivity toothpastes, "You need to keep using them to maintain the effect"10, which is sound advice for a whole population even though the few measurements of stopping turned out gentler than it implies.
The table sets every measured pattern of stopping, pausing and occasional use side by side, with who paid for each, and ends with the patterns nobody has measured. S3 is in the last row because it has no published trial of stopping, episodic or as-needed use, only the design of a paste meant for every day.
| Pattern of use | Study: design, size, who paid | Active | What was measured, and when | What was found |
|---|---|---|---|---|
| Stopped after eight weeks; three weeks on a plain paste | Biesbrock 2025: double-blind randomised trial, 120 adults; funded by Procter & Gamble1 | Potassium nitrate (stannous fluoride and oxalate arms too) | Cold air and probe at week 8, then at week 11 | Advantage over the plain paste 44.3% then 35.8% on cold air, 104% then 72.5% on the probe; significant at both visits |
| Stopped after eight weeks of supervised use; twelve weeks off | Gillam 1992: follow-up of a randomised trial, 40 adults; no funder named in the record2 | Strontium chloride, two pastes of different abrasivity | Probe, cold air and a pain scale twelve weeks after stopping | Drifted back slightly; still significantly below baseline; no placebo group |
| One day off after four weeks | Ishii 2026: double-blind randomised trial, 127 adults; authors employed by Lion Corporation, the manufacturer, or funded by it9 | 5% potassium nitrate | Probe and air at week 4 and 24 hours later | Probe threshold 22.88 g then 24.63 g, air score 1.75 then 1.58; the placebo arm moved the same way |
| Two eight-week courses with eight weeks on an ordinary paste between, against 24 weeks of daily use | Mason 2017: examiner-blind randomised trial, 76 adults; sponsored by GSK Consumer Healthcare3 | 5% calcium sodium phosphosilicate (bioactive glass) | Cold-air score (0 to 3), probe and questionnaires at weeks 8, 16 and 24 | Change from baseline −0.36 against −0.26 at week 8; −0.24 against −0.39 at week 16, after the eight weeks off (not significant); −0.48 against −0.47 at week 24; little change on the probe or in self-report |
| One fingertip application in a clinic, then three days of brushing | Ayad 20095, Nathoo 200911, Fu 201012: double-blind randomised trials; authors include scientists employed by the arginine paste's maker | 8% arginine, with a potassium paste as benchmark in two | Probe and air just after the application, and at day 3 | Arginine groups less sensitive than the plain paste, and than the potassium benchmark, just after the application |
| One self-applied dab in a clinic, then three days of brushing | Mason 2010: examiner-blind randomised trial, 79 adults; first author employed by GSK Consumer Healthcare6 | 8% strontium acetate | Air, probe and a pain scale just after, and at day 3 | Ahead of a plain fluoride paste at both times; the plain paste reduced sensitivity too |
| One fingertip application in a clinic, then three days of brushing | Creeth 2019: three examiner-blind randomised studies, 667 people; sponsored by GSK Consumer Healthcare7 | 0.454% stannous fluoride | Air and probe just after, and at day 3 | Ahead of the control in two studies; no significant difference in the first, of 230 people, at either time |
| A strip used a few times, against a potassium nitrate paste brushed daily | Amini 2016: randomised trial, 79 adults; three of four authors employed by Procter & Gamble, which makes the strip13 | 1.5% oxalate strip against 5% potassium nitrate paste | Air and probe after the first use and at day 30 | Only the strip group improved after the first use; the day-30 comparisons favoured the strip |
| A potassium nitrate paste used only when it hurts | No trial found | — | — | PubMed searches, 10 September 2026: 12, 23 and 4 records, none on this |
| Any paste used again and again at home, only on bad days | No trial found | — | — | The same searches; every single-application trial measured one use in a clinic |
| S3: no trial of stopping, episodic or as-needed use | Not studied | 5% potassium nitrate, two hydroxyapatites, 1450 ppm fluoride | — | — |
Does using it on and off work as well as using it every day?
In the one trial that tried it, on-and-off use ended level with daily use, though neither schedule did much, and because it is the only such trial it is worth reading closely.
It was run in Cork and sponsored by GSK Consumer Healthcare, which makes the paste it tested; the first author is a company employee and the other authors' research centre had received company funding3. Seventy-six adults aged eighteen to forty-eight, each with two sensitive test teeth, were randomised to the manufacturer's 5% calcium sodium phosphosilicate paste, a bioactive glass, brushed twice a day3. Half used it for twenty-four weeks without a break. The other half used it for eight weeks, switched to an ordinary fluoride paste with no known desensitising action for eight weeks, then went back to the test paste for the final eight. Brushing was supervised at every visit and logged in a diary, which is tidier than use at home is likely to be.
Cold air was scored on the Schiff scale, which runs from nought to three, and both groups started a little above two. By week eight both had improved slightly on the manufacturer's measure, by 0.36 of a point in the stop-start group and 0.26 in the daily group3.
Week sixteen is the reading this page cares about most, because the stop-start group had just spent eight weeks on the ordinary paste. Its improvement had shrunk to 0.24 of a point, still significantly better than at the start, while the daily group had moved on to 0.39; the gap between them, 0.15 of a point, was not statistically significant in the manufacturer's analysis (p = 0.17)3. So eight weeks off cost the stop-start group something you could see in the averages and could not separate from chance. After its second eight-week course the two groups were level, at 0.48 and 0.47 of a point below baseline at week 24, in the manufacturer's own figures3.
On the probe test neither schedule changed significantly, and the questionnaires people filled in about their own teeth, including a weekly sensitivity question, showed little or no change in either group across the six months of the manufacturer-sponsored trial3. The authors, one of them employed by the manufacturer, describe the improvements as small and call the lack of any difference between schedules unexpected, offering the small change in both arms as one likely reason3. Writing for a manufacturer, they also make the point this page is built on: people with sensitive teeth probably use these pastes on and off as symptoms come and go, and the way trials are designed has not reflected that3.
What nobody has studied is the pattern most readers describe. A tube opened when a cold snap or a bad week sets the teeth off, used until things settle, and put back in the cupboard until the next time. The stop-start arm in that trial kept to a fixed eight-week timetable under supervision, and the single-application designs in the next section consist of one use in a clinic followed by a few days of ordinary brushing. PubMed searches run for this page on the tenth of September 2026, for as-needed, on-demand, intermittent and episodic use of a desensitising toothpaste, returned twelve, twenty-three and four records, and none of them describes repeated use at home only when it hurts.
The one trial that compared episodic use with daily use over 24 weeks, a bioactive-glass study of 76 adults sponsored by GSK Consumer Healthcare in which both schedules produced only small improvements on cold air, found no difference between them, and that weakens the case for a daily toothpaste like S33.
Does a single application help when it hurts?
In a clinic, for some actives, one application reduced sensitivity to a probe and a puff of air; as a routine at home, and for potassium nitrate, nobody knows.
Three double-blind randomised trials published in 2009 and 2010 had people in Mississauga, New Jersey and Chengdu apply an 8% arginine paste once to two sensitive teeth with a fingertip, for a minute, then measured them immediately after that single application and again after three days of ordinary brushing; the records name no funder, and their authors include scientists employed by the company that makes the arginine paste51112. In all three of those manufacturer-linked trials the arginine groups were measurably less sensitive straight afterwards than the groups given a plain fluoride paste the same way51112. The Chengdu figures, from a trial co-authored by the manufacturer's scientists, show the size of it: on the air-blast score the arginine groups went from about 2.1 to about 1.2 after the one application, while the plain fluoride group went from 2.15 to 2.0612.
Two of those trials also applied a potassium paste once, as a benchmark described only as containing 2% potassium ion, and in those manufacturer-run trials it did less than arginine immediately after the application511. More to the point, one application judged within minutes is not how a potassium nitrate paste is meant to be used, and its evidence comes from weeks of brushing.
The same design has been run with other actives. In an examiner-blind randomised trial of 79 adults, led by an author employed by GSK Consumer Healthcare, an 8% strontium acetate paste dabbed onto sensitive teeth was ahead of a plain fluoride paste immediately afterwards on cold air, the probe and a self-rated scale, although the plain paste reduced sensitivity as well6. Stannous fluoride gives the most useful result, because one of the three attempts came up empty. Three examiner-blind randomised studies sponsored by GSK Consumer Healthcare, 667 people in all at UK sites, had participants apply a stannous fluoride paste by fingertip to two sensitive teeth for a minute each; in two of the studies the paste was ahead of an ordinary fluoride paste immediately after that single application, and in the first, of 230 people, there was no significant difference then or after three days7.
The one randomised comparison of a product used episodically against a potassium nitrate toothpaste used every day did not involve an episodic toothpaste at all. In a thirty-day trial of 79 adults, three of whose four authors are employed by Procter & Gamble, which makes the strip, a 1.5% oxalate strip used a handful of times gave relief after the first use that the daily 5% potassium nitrate paste did not, and at day 30 the comparisons favoured the strip13. It is a strip, not a paste, and it was tested by its maker.
Put together, the evidence for using something only when it hurts is a set of single applications in clinics, of arginine, strontium acetate and stannous fluoride, plus one strip. None of it applied potassium nitrate as the test paste. None of it followed a paste used again and again at home on bad days only. Almost all of it was produced by the companies selling the products. Applying paste to a sore spot as a routine is a separate question, and this page gives no instructions for it; for the first evening of a flare, the guide to what helps tooth nerve pain tonight is the place to start. Every paste discussed here is meant to be brushed on and spat out.
Why does restarting feel like it is not working?
Because a restart puts you back in the weeks where the effect is smallest and hardest to tell apart from a flare settling by itself.
In the trial funded by Procter & Gamble that included the washout arm, the potassium nitrate paste was already ahead of the plain control on cold air at day three and 20.4% ahead at week two, and on the probe it had not separated at all at day three, where its 10.7% was not significant1. By week four the manufacturer's tables show 34.6% on cold air and by week eight 44.3%, and the share of people with at least one test tooth that stopped reacting went from none at day three to 3% at week two, 7% at week four and 28% at week eight1.
A systematic review of 74 randomised trials, which grouped desensitising treatments by when their effect first reached significance, placed potassium nitrate only in its long-term group; no toothpaste of any kind made its first-week group, which held only treatments applied in the dental chair8.
The plain control paste in that washout trial moved too, and most of its movement came early: in the manufacturer's adjusted figures its cold-air score went from about 2.45 at the start to 2.24 at week two and then barely shifted to week eight1.
Now lay a stop-start habit over that timetable. The tube comes out when a cold snap or a bad week starts. It is used for a week or two while the teeth are at their worst, and it goes back in the cupboard as they calm down. Almost all of that use falls in the fortnight where the potassium paste had barely separated from a plain one, and the settling felt in that fortnight could as easily be the flare passing, or the share of improvement a plain paste also gets, as anything the active has done. So the paste is judged on the weeks least able to show what it does, and the brand takes the blame.
Searches run for these pages found no record of anyone timing how long a flare of sensitivity lasts on its own, so this page cannot tell you how much of a good week was the flare passing. The page on why relief builds over weeks explains the slow start, the page on how long to give a new sensitivity toothpaste sets out a fair test, and if your pattern follows the seasons, the page on sensitive teeth in winter is written for you.
Does a daily-use paste like S3 make stop-start use pointless?
No trial says so, and this page will not say it either.
A daily design assumes the actives need to be there day after day to build up. S3 is made as the toothpaste you use every day, not a fortnight's treatment. Its own description is of relief that builds over weeks, with potassium gathering around the nerve and mineral laid down brush by brush, and it is judged at two to four weeks.
The one regimen trial does not take the side of that assumption. In that manufacturer-sponsored trial a bioactive-glass paste used in two courses with a break between ended level with the same paste brushed daily3. No trial has tested S3 stopped, used stop-start or used only when it hurts. If the stop-start habit is the reason a paste never seemed to work, switching to S3 does not fix that habit; using any paste every day for eight weeks might.
What S3 changes is the mechanism, not the routine: it carries potassium nitrate for the nerve and hydroxyapatite for the open tubules, and neither active does the other's job. That is a reason to consider it once a fair daily run of one mechanism has not been enough, and no reason to expect it to work in bursts.
So is it the brand, or the way you use it?
Often it is the way the paste is used, and the market leader says as much about its own tubes.
On its UK FAQ page, Sensodyne states that "if you stop brushing with Sensodyne toothpaste, your sensitivity can return, so it is best to make Sensodyne your daily toothpaste to care for sensitive teeth". The same page says "it's important to continue brushing with Sensodyne toothpaste twice a day, every day, for lasting tooth sensitivity relief". Those are the brand's statements about its own products. They are worth reading because they come from the paste a reader may be about to leave: its maker's advice is daily use, not use when it hurts. This page makes no judgement of how that brand's pastes perform.
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.
The fair test is the one trials use. Trials in this condition are built to a 1997 consensus that asks for eight weeks of use in most studies, with follow-up afterwards to see whether a change lasts4. For a reader that means one paste, brushed morning and night every day for eight weeks, with the start date written down, the cold-drink test noted once a week, and no drifting back to an ordinary paste when the teeth feel calmer.
If eight weeks of daily use of one mechanism was not enough, change the mechanism, not the name on the tube. The guide to Sensodyne alternatives by active ingredient sorts the UK shelf by what is inside, and the page on what to try when Sensodyne stops working sets out an order to try things in. The Journal covers the mechanisms from the other side in how sensitive toothpastes work and why yours might not be working.
Expect to run the test alone. In a qualitative interview study of 18 Australian adults with confirmed sensitivity, supported by Haleon, a toothpaste manufacturer, 89% were using a desensitising toothpaste and every one of them had picked it without a dentist's advice14.
And if the pain has changed its character instead of simply coming back, the question is not which paste any more. The Oral Health Foundation asks people to see a dentist when the pain is severe, when sensitivity carries on beyond a few weeks, when a single tooth is affected or when it starts suddenly10.
Frequently asked questions
Can I use S3 only when my teeth hurt?
Nobody has tested S3 used that way, so there is nothing to tell you how it would do. It is made to be the toothpaste you brush with every day, not a treatment to take in bursts. What the industry-funded stop-start trials of other pastes suggest is that the cost of using a paste on bad days only is the restart, the slow first weeks every time, rather than a sudden loss when you stop13. S3 is brushed on and spat out like any toothpaste, and this page describes no other way of using it.
How long after stopping does sensitivity come back?
Slowly, as far as anyone has measured. In a double-blind randomised trial funded by Procter & Gamble, a potassium nitrate group kept most of its advantage over a plain paste three weeks after switching to one1. In a 1992 follow-up of 40 adults, sensitivity had drifted back only slightly twelve weeks after they stopped a strontium paste2. Nobody has measured potassium nitrate beyond three weeks off, or any paste beyond twelve.
Is there a sensitivity toothpaste that works the same day?
In a clinic, after a single application, some have been measured doing something: arginine, strontium acetate and stannous fluoride pastes, in trials run or co-authored by scientists employed by their manufacturers, were ahead of plain fluoride pastes immediately afterwards, although one of three stannous fluoride studies found no difference567. Potassium nitrate has not been tested that way, and in a brushing trial funded by Procter & Gamble it had not separated from a plain paste on the probe test by day three1. None of those measurements was of a paste used at home on bad days only.
Should I switch brand if my paste never seemed to work?
Not first. If the tube only came out on bad days, it has never had a fair run. Give one paste eight weeks of daily brushing, the length trials in this condition are built around, and switch only if that was not enough; then switch mechanism, from a nerve active to a tubule-sealing one or to a paste with both, rather than to another brand of the same active4.
Is it harmful to keep switching back to a normal toothpaste?
No study this page found reports harm from moving between a sensitivity paste and an ordinary one, and in the manufacturer-sponsored stop-start trial the eight weeks on an ordinary fluoride paste were part of the design3. What matters more is keeping fluoride in the routine whichever tube is in use, and spitting out after brushing without rinsing, as the Oral Health Foundation advises10.
Where S3 sits
The answer to stop-start use is a daily run long enough to judge, not a new brand, and S3 is made for daily use: a toothpaste for every day rather than a fortnight's course, judged at two to four weeks. If eight weeks of one mechanism has not been enough, the switch that changes something is to add the other, and S3 carries potassium to desensitise the nerve and hydroxyapatite to occlude the tubules, neither doing the other's job.
S3 Sensitivity Science™ pairs potassium nitrate with two hydroxyapatites and adult-strength fluoride in one daily paste.
See the toothpasteS3 Sensitivity Science™ makes one daily toothpaste that holds 5% potassium nitrate, for the nerve, beside 10% nano-hydroxyapatite and 5% biomimetic hydroxyapatite (both as solution) and full adult-strength fluoride. The formula is designed around three actions: calm the nerve, strengthen the enamel surface, and protect against further wear. S3 Repair Technology™, the name given to that formula, is patent-pending under UK application GB2604755.5. More than 20 UK dentists are among the owners of S3, having put money into it instead of lending it their names. Read more about S3.