Hydroxyapatite or Fluoride Toothpaste: What the Research Says About Enamel Remineralisation

Tooth decay is a process of demineralisation: bacteria in dental plaque ferment sugars into acids that dissolve enamel mineral (calcium hydroxyapatite). A healthy mouth balances this with remineralisation — calcium and phosphate ions from saliva are built back into damaged enamel. Decay develops when demineralisation outweighs remineralisation for a prolonged time.

Fluoride acts in several ways at once, and the mechanism is well understood. Fluoride ions present in saliva and plaque are incorporated into the rebuilt mineral, forming fluorohydroxyapatite and fluorapatite, which are less soluble in acids than hydroxyapatite itself. Fluoride also speeds up the remineralisation of early lesions and can inhibit the metabolism of acid-producing bacteria. The effect is mainly local, at the tooth surface, which is why regular contact of a low concentration of fluoride with the teeth matters, not swallowing it.

The clinical effectiveness of this mechanism is confirmed by trials involving tens of thousands of participants, usually lasting 2–3 years. It is this scale that distinguishes fluoride from most other toothpaste ingredients.

Two conclusions are important. First, there is a dose effect: a higher fluoride concentration gives slightly greater protection. Second, this review contains no evidence that concentrations above about 1500 ppm give further benefit. The specific recommendations on toothpaste concentration and amount depend on age and national guidelines, which are worth checking with a dentist.

Fluoride also has a known drawback: in small children who swallow toothpaste, excess fluoride during tooth development can cause fluorosis (changes in enamel, most often mild, in the form of whitish patches). The 2010 Cochrane review on this topic (later updated, so it is worth checking current guidelines) indicated that the risk concerns mainly small children, that most of the evidence concerns mild fluorosis, and that if the risk is a concern, a concentration lower than 1000 ppm is recommended for children under 6. This is one of the real reasons why parents look for alternatives — we write about fluoride in water separately in our article on fluoride in drinking water.

Hydroxyapatite is the same mineral of which enamel is predominantly made. Toothpastes use its synthetic, finely ground form (often called biomimetic hydroxyapatite or nano-hydroxyapatite). The idea is simple: if a tooth loses mineral, supply it in ready-made form. The microparticles are meant to settle on the enamel surface, fill micro-defects and form a protective layer, as well as serve as a local source of calcium and phosphate in an acidic environment.

This is a different mechanism from fluoride. Fluoride changes the properties of the mineral being rebuilt, making it more resistant to acids. Hydroxyapatite would be 'adding bricks'. The advantage is that the ingredient is non-toxic if swallowed, which makes it an attractive choice for small children. The disadvantage — so far — is that it is not certain how many of these particles actually reach damaged sites and whether the effect translates into fewer cavities in everyday life.

This review is important because it is the largest available attempt to pool the data, and its conclusion is encouraging. But three things are worth noticing. First, 'better than placebo' and 'similar to fluoride' are two different statements: the comparison with fluoride was not statistically significant, so it does not show an advantage, only a lack of detected difference in small samples. Second, a substantial part consisted of in situ studies, which measure surrogates of decay (for example lesion depth) rather than the number of new cavities. Third, some of the authors have ties to a manufacturer — which does not invalidate the conclusions, but requires independent confirmation.

Other teams have tried to provide such independent verification. A 2025 review focused on children, adolescents and young adults under 25 found only 4 suitable (randomised) in situ studies comparing fluoride-free hydroxyapatite toothpastes with fluoride toothpastes. The development of new lesions and the progression of existing ones did not differ significantly between groups (RR 0.98; 95% CI 0.85–1.12; OR 0.90; 95% CI 0.57–1.42). The authors considered hydroxyapatite a promising option for people seeking fluoride-free products.

The most frequently cited study is a Polish randomised trial from 2021 that compared a toothpaste with microcrystalline hydroxyapatite (fluoride-free, used three times a day) with a fluoride toothpaste in children over 336 days. 207 children were included in the analysis. An increase in carious lesions (ICDAS ≥ 1) was seen in 72.7% of children in the hydroxyapatite group and 74.2% in the fluoride group. The authors concluded that the hydroxyapatite toothpaste was not inferior to the fluoride one within the adopted non-inferiority margin (20 percentage points).

How to read this? On the one hand, it is one of the few clinical trials in this area, carried out in a paediatric population and giving a result in favour of equivalence. On the other, a margin of 20 percentage points is wide, follow-up lasted less than a year, the groups were small, and lesion increase exceeded 70% in both groups — meaning that in most children decay progressed regardless of the toothpaste used. On its own the study does not settle whether hydroxyapatite toothpaste is equally effective over the longer term.

For parents the most important point is that choosing a toothpaste is only part of preventing decay in children: also important are limiting the frequency of snacking and sugary drinks, careful brushing with an adult's help, and regular dental check-ups. A fluoride toothpaste at an age-appropriate concentration, used in an appropriate small amount and without swallowing, has the largest body of evidence. If a parent is considering a hydroxyapatite toothpaste, for example because of concerns about swallowing, it is best to discuss it with a paediatric dentist, who assesses the individual caries risk.

Many patients look for hydroxyapatite toothpaste because they want to 'rebuild' white spots after braces or early carious lesions. A 2024 meta-analysis on the effect of nano-hydroxyapatite on white spot lesions (14 papers, of which 10 were in vitro studies, 3 in vivo and 1 in situ) pointed to a promising increase in enamel microhardness and mineral gain compared with fluoride alone, but no improvement in the colour of the lesions. The authors cautioned that the small number of clinical studies, the high risk of bias and the short follow-up do not allow strong conclusions.

In practice this means two things. First, early carious lesions (white spots) can be stopped or partially reversed, but this happens through better hygiene, less sugar and regular access to fluoride or other remineralising agents — not through one magic toothpaste. Second, 'rebuilding' a cavity that already has an open hole is not possible with toothpaste: such a tooth needs treatment at the dentist. Toothpaste will not replace a filling.

It is also worth remembering that when choosing a toothpaste, regularity matters most: thorough brushing twice a day, limiting how often you eat sugars and cleaning the interdental spaces (we compare the tools in our article on the water flosser and floss). Differences between good toothpastes usually have less impact than habits.

If we had to choose one toothpaste for a typical adult with no particular concerns, it would be a fluoride toothpaste, because it has the strongest evidence. Hydroxyapatite is a reasonable option for people who, for some reason, do not want fluoride (for example parents of small children worried about swallowing), provided they understand that the evidence base is narrower and that it does not replace other elements of prevention. For people with a high caries risk the decision is best made together with a dentist.

Interestingly, the two approaches need not be mutually exclusive. Well-designed, independent and long comparative trials would clarify whether hydroxyapatite matches fluoride, and even whether combining them gives an additional benefit. Until then it is honest to say: fluoride — proven, hydroxyapatite — promising.