In toothpaste, hydroxyapatite works in preventing cavities and reducing teeth sensitivity by adhering/inserting itself into the enamel since it is biomimetic. These two effects make it a suitable replacement for fluoride as an anti-cavity and anti-sensitivity toothpaste.
As with everything in life, there are trade-offs and no toothpaste ingredient is flawless so there are pros and cons to using it.
How hydroxyapatite works for cavities
Hydroxyapatite (HAP) works as an anti-cavity agent by remineralizing small carious lesions, resisting enamel dissolution, serves as a tooth mineral reservoir, and anti-bacterial adhesion.
Remineralization. It can directly insert itself into incipient carious lesions to replace missing tooth minerals. Since minerals are being added back into the enamel, it is called remineralization.
Enamel protection. It can adhere to the surface of the enamel and form a protective barrier which serves as a sacrificial layer during acidic attacks.
Mineral reservoir. The layer of hydroxyapatite over the enamel when it dissolves, it will release calcium and phosphates which can help buffer the oral environment. This brings the pH back to neutral and away from the critical pH level of when enamel dissolves.
Anti-bacterial adhesion. Can reduce plaque formation by directly binding to bacterial, thereby preventing bacteria from binding to your enamel.
The diagram below shows how HAP can remineralize teeth.
The diagram below shows how HAP can prevent bacteria from adhering to the enamel by directly binding to them.
When to expect improvement: The time it takes to remineralize a small cavity can take weeks to months. The only way to verify that it is working is by taking x-rays at each dental checkup visit to compare the lesion size.
How hydroxyapatite works for sensitivity
Hydroxyapatite (HAP) works in reducing teeth sensitivity by occluding open dentinal tubules, which blocks external stimuli from interacting with the tooth nerve.
How it works: Hydroxyapatite can occlude open dentinal tubules by directly inserting itself into the patent tubules. It also adheres to the surfaces of the teeth since it is made of the same substance as enamel. Yes, enamel is composed of 97% HAP and that's why it is biomimetic.
Why it helps: When dentinal tubules are unoccluded/open, it allows external stimuli to directly stimulate the tooth nerve. That means drinking hot/cold/sweet/spicy/acidic will elicit pain/sensitivity. However, when you block/close the tubules, the stimuli will be unable to interact with the tooth pulp.
This exact mechanism is why whitening your teeth creates sensitivity. The bleaching gel dissolves the smear plugs thus opening the dentinal tubules. Thus, the gel can directly stimulate the nerve.
When to expect improvement: HAP can occlude your teeth within moments of the toothpaste contacting the enamel. However, you should brush with it diligently for at least 1-2 days to see its full effect. Although you do need to use it continuously in order to maintain it because an acidic diet will dissolve these newly hydroxyapatite occluded tubules.
Suitable fluoride alternative
Toothpastes with hydroxyapatite are considered a valid alternative for fluoride based toothpastes but it has yet to be recognized by the ADA.
What makes it a valid alternative:
Anti-cavity effects. It can help prevent cavities, protect teeth from acidic attacks, and even remineralize small carious lesions.
Similar remineralization efficacy. Studies have shown that its remineralization efficacy is at least equivalent to fluoride.
Essentially this toothpaste ingredient can do just about almost everything that fluoride can do for your teeth. Although fluoride does have one benefit which this doesn't.
Catch 22: Despite wonderful results from scientific studies, HAP isn't FDA approved as an anti-cavity agent and thus, the American Dental Association cannot explicitly recommend it as such.
The reason why has more to do with the history of the founding of this substance.
HAP was discovered by NASA in the 1960s.
NASA sold the patent to a Japanese company, Sangi Co which made the first hydroxyapatite toothpaste in the 1970s.
These toothpastes have been in use in Japan since the 70s.
HAP made its way to Europe in the early 2000s and finally re-emerged in the US around 2010s.
Apparently, running tests/studies to get this FDA approved is cost-prohibited and no toothpaste company wants to do it at the moment. There is also the fact that fluoride works just as well and is dirt cheap.
Pros/Cons
There are advantages and disadvantages to using hydroxyapatite instead of fluoride in toothpaste.
Pros:
Equivalent efficacy. Research has shown it to be just as effective as fluoride.
Safer. It's not possible to be allergic to HAP and you don't have to worry about fluoride toxicity.
Natural. Our teeth and bones are naturally made of it, which is why it is considered a biomimetic substance.
Cons:
Costly. Toothpastes with HAP tend to come with a price premium, often costing much more than regular fluoride ones. On average it costs about $10-12 but we've also seen some greater than $20 for a small tube.
Verdict
Hydroxyapatite works by adhering to your enamel and protecting it from cavities and sensitivity. It is able to do so since your enamel is made of it so it has a natural bond to it.
With that being said, despite brushing with HAP toothpaste twice a day it is still recommended to get routine dental checkups. Our dentists in Long Island City recommend biannual or 6 month oral exams for optimal oral health.
