Enamel doesn't grow back. This is one of those facts most people have heard from a dentist, and it's true — enamel-forming cells are only active during tooth development. Once adult teeth emerge, the body cannot produce new enamel.
But that is not the whole story. Enamel loses and regains minerals every day, and that balance is what dentists mean by demineralisation and remineralisation. This guide explains the process in plain language and summarises the published research on hydroxyapatite, the ingredient most often studied in fluoride-free toothpaste.
Why Enamel Gets Damaged
The mouth operates on a constant acid cycle. Every time you eat or drink, the bacteria in plaque metabolise sugar and carbohydrates and produce acid as a byproduct. Acid with a pH below about 5.5 begins dissolving the mineral crystals in enamel — this is demineralisation.
Under normal conditions, saliva neutralises the acid and provides calcium and phosphate that allow the enamel to regain minerals. Problems arise when the acid outpaces the recovery: frequent snacking, a high-sugar diet, acidic drinks, dry mouth, or acid reflux can all tip the balance toward net mineral loss.
The early visible sign of this imbalance is a white spot — a chalky, opaque patch on the enamel surface. Dentists describe this earliest stage as potentially reversible. Left unchecked, it can progress to a cavity: a hole in the tooth that needs treatment from a dentist. This is one reason regular check-ups matter.
What Remineralisation Actually Is
Remineralisation is the return of calcium and phosphate to enamel that acid has softened. It is not enamel regeneration — no new enamel is grown — but it is a normal, daily process.
Saliva is the body's own remineralisation tool. It naturally carries calcium and phosphate and goes to work as soon as the mouth becomes less acidic. This is why saliva flow matters, and why people with dry mouth are generally at higher risk of cavities.
Toothpaste can supplement this process. Fluoride is the ingredient with the longest track record for doing so, and it is what dental organisations recommend. Hydroxyapatite is the most-studied fluoride-free alternative.
Where Hydroxyapatite Comes In
Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) is the calcium phosphate mineral that tooth enamel is mostly made of. Because it is the same mineral, researchers have studied whether synthetic hydroxyapatite in toothpaste can support remineralisation. It is used in toothpaste in different particle sizes, usually described as micro or nano.
Researchers have looked at two main questions: what hydroxyapatite toothpaste does for early enamel lesions, and what it does for sensitivity, where the particles are thought to cover the tiny open channels (dentinal tubules) in exposed dentine.
What the Published Research Shows
These are studies of hydroxyapatite as an ingredient. None of them was conducted on ENML products.
- Amaechi et al. (2019, BDJ Open): in a randomised crossover study, 30 adults wore small blocks of tooth enamel in the mouth while using either a 10% hydroxyapatite toothpaste or a 500 ppm fluoride toothpaste. Both toothpastes remineralised artificially created early lesions, with no statistically significant difference between them. Read the study.
- Paszynska et al. (2021, Scientific Reports): a one-year randomised clinical trial in children found that a microcrystalline hydroxyapatite toothpaste was not inferior to a fluoride toothpaste in the progression of early caries in primary teeth. Read the study.
- Limeback, Enax and Meyer (2021, Canadian Journal of Dental Hygiene): a systematic review and meta-analysis of clinical trials concluded there is good evidence that hydroxyapatite in fluoride-free oral care products reduces caries. Only three randomised trials could be pooled, and two of the three authors work for a company that makes hydroxyapatite toothpaste. Read the review.
- Chatzidimitriou et al. (2025, Journal of Dentistry): a systematic review of four trials in children, adolescents and young adults found no significant difference between hydroxyapatite and fluoride toothpastes in the development or progression of early lesions. Read the review.
- Limeback, Enax and Meyer (2023, Biomimetics): a systematic review and meta-analysis of 44 clinical trials on dentine hypersensitivity reported that hydroxyapatite in oral care products reduced sensitivity compared with placebo and with fluoride. The same author affiliations apply. Read the review.
- Pepla et al. (2014, Annali di Stomatologia): a literature review of nano-hydroxyapatite in dentistry, useful as background on how the ingredient has been used.
Important context: the number of long-term clinical trials on hydroxyapatite is still small compared with fluoride's 70-year track record. Several studies were funded by, or written with, toothpaste manufacturers. And each study tested a specific formulation, so results cannot be assumed to apply to every product that contains hydroxyapatite.
Hydroxyapatite and Fluoride at a Glance
| Hydroxyapatite | Fluoride | |
|---|---|---|
| What it is | The calcium phosphate mineral that enamel is mostly made of | Fluoride compounds such as sodium fluoride |
| Status in US toothpaste | Cosmetic ingredient | Anticavity active ingredient in over-the-counter drug toothpaste |
| Evidence base | Growing — laboratory and in-mouth studies, plus a small number of clinical trials | Extensive — 70+ years, including population-level studies |
| Who recommends it | Some dentists, for patients who prefer fluoride-free | The ADA and most dental organisations |
The honest summary: fluoride has the deepest evidence and is what dental organisations recommend for cavity prevention. Hydroxyapatite is the most-studied fluoride-free alternative, with research that is promising but younger. If you are at high risk of cavities, talk to your dentist before going fluoride-free.
Where ENML Fits
ENML Mint Toothpaste Tablets are fluoride-free tablets made with 10% micro-hydroxyapatite — the same mineral as tooth enamel. The formula was developed by a dentist for people who want a considered, fluoride-free routine. ENML tablets are cosmetics: they clean and polish teeth and freshen breath. We do not claim that they treat, reverse or prevent cavities or sensitivity. Explore ENML Mint Toothpaste Tablets or ENML Whitening Tablets.
Frequently Asked Questions
Can toothpaste actually rebuild enamel?
No toothpaste can grow new enamel — the cells that form enamel are gone once a tooth has developed. What researchers study is remineralisation: minerals returning to enamel that acid has softened. Saliva does this naturally every day, fluoride toothpaste has a long record of supporting it, and hydroxyapatite toothpaste is being studied for the same purpose.
What should I use if I'm worried about cavities?
Talk to your dentist. Fluoride toothpaste is the standard recommendation of the American Dental Association for cavity prevention. If you prefer to go fluoride-free, hydroxyapatite is the most-studied alternative ingredient; the research is summarised above.
What does the research say about hydroxyapatite and sensitive teeth?
A 2023 systematic review of 44 clinical trials reported that oral care products containing hydroxyapatite reduced dentine hypersensitivity. Those trials were not conducted on ENML products, and ENML does not make sensitivity claims. If sensitivity persists, see your dentist to find the cause.
Can early cavities be reversed?
Dentists describe the earliest stage of decay — a white spot on the enamel surface — as potentially reversible through remineralisation. Once it has become a hole in the tooth, it needs treatment. Only a dentist can tell you which stage you are dealing with.
Is hydroxyapatite toothpaste fluoride-free?
Usually, although some toothpastes contain both. ENML tablets are fluoride-free and made with micro-hydroxyapatite.
Keep reading: Micro vs Nano Hydroxyapatite: Why Particle Size Matters, or Fluoride Free Toothpaste: Is It Safe?
A note on the research referenced on this page
The studies referenced here examine hydroxyapatite as an ingredient and are provided as publicly available scientific literature for general information — they are not claims about ENML products. ENML products are cosmetics: they clean and polish teeth and freshen breath, and are not intended to diagnose, treat, cure, or prevent any disease or condition. For questions about your oral health, talk to your dentist.