Nano-hydroxyapatite is a remineralizing toothpaste ingredient which has anti-cavity effects comparable to fluoride which makes it a fluoride-free alternative.
Table of contents:
Overview
Hydroxyapatite benefits are derived from the fact that your teeth are practically made of the same exact material, calcium apatite [Ca10(PO4)6(OH)2]. As a matter of fact, the enamel is made of 97% hydroxyapatite so when you brush with it, you're using the same mineral as your enamel to repair it.
Differences between nano-hydroxyapatite in toothpaste vs your teeth:
The particles are smaller which is why they're called "nano".
It is synthetically made.
Nonetheless, it is virtually the same substance as your teeth except they're sized smaller. Studies have found it to be more effective when it's a smaller size since it can enter into the tubules and defects more easily.
Background information: Hydroxyapatite may sound new but it has actually been around since the 1970s. NASA was trying to come up with a solution to prevent astronauts from losing bone mineral density while in space and that was how it was discovered.
They sold the patent to a Japanese company, Sangi Co who eventually created the first hydroxyapatite toothpaste in 1978. Thus, it's been used in Japan for decades so it isn't a new product by any means.
How nano-hydroxyapatite helps teeth
The nano-hydroxyapatite is virtually identical to the hydroxyapatite that is naturally found in enamel and dentin. After all, hydroxyapatite is the primary mineral in teeth and bones. This means that this toothpaste ingredient is highly biocompatible, biomimetic, and non-toxic.
Benefits of hydroxyapatite for teeth:
Remineralizes teeth
Reduces plaque formation
Reduces teeth sensitivity
Whitens teeth
Teeth remineralization
Hydroxyapatite toothpastes have demonstrated remineralization capabilities that were comparable to fluoride with no statistical difference. Since the efficacy in enamel repair was similar, hydroxyapatite is often marketed as being a fluoride alternative but the remineralization mechanism is different from fluoride.
Replace demineralized enamel. In demineralized enamel, nano-hydroxyapatite inserts itself into the tooth to replace the missing minerals, calcium and phosphate.
Reservoir for minerals. In dentin, it penetrates into the collagen matrix and acts as a scaffold by providing calcium and phosphate locally.
Buffers oral environment. It forms a synthetic enamel layer that covers the tooth which can act as a buffering solution when under acidic challenges.
Directly replace the missing minerals
When acids dissolve the enamel, it loses minerals in a process called demineralization. What nanohydroxyapatite can do is directly replace those lost minerals by inserting itself into the deficient areas.
It is able to replace the dissolved minerals because it is made of the same ones as the tooth. It is practically an identical replacement when this occurs.
This is different from how fluoride remineralizes which has to draw in calcium and phosphates to complete the enamel repair. The hydroxyapatite does not need to draw in additional minerals since it already has them in its structure!
Provide minerals locally
For demineralized dentin, the nanohydroxyapatite acts as a scaffold in the collagen matrix. It will provide the missing minerals to the local surroundings.
Despite being able to repair the dentin, we don't believe it is very likely to do so in vivo. The reason is because small cavities are typically reversible when they're still in the enamel but not so much so once they reach the dentin. There is a general consensus in the dental community that decay is irreversible once it reaches the dentin or at least we haven't seen it happen yet.
Buffers oral environment
In addition to repairing the enamel by replacing the missing minerals, nano hydroxyapatite will also form a synthetic layer over it. It will literally come together and form a covering over the tooth structure to protect it.
What this layer does is act as the first line of defense against acid challenges. It will get dissolved first, thus protecting the actual enamel layer underneath. Once it dissolves it will release the minerals that it is made of, calcium and phosphate.
The unbound phosphates act as a buffer to deacidify acids in the mouth. It will combine with protons to remove them from the oral environment. Less protons means the mouth will become less acidic and that ultimate means the teeth will stop demineralizing.
Studies have shown that the phosphate system is one of saliva's buffering mechanisms. It may not be the primary one but it assists when the need arises. The bicarbonate is the primary buffering system in your mouth.
Reduces plaque formation
Studies have shown that hydroxyapatite is effective in oral biofilm management by reducing plaque formation on the enamel surfaces. However it seems to act as more of an anti-adhesive rather than an antibacterial, which means that it does not kill bacteria. It merely prevents bacteria from sticking to surfaces that we don't want them to.
The hydroxyapatite can directly bind to the bacteria.
It binds to the enamel pellicle receptors, which prevents bacteria from binding to it.
The nano hydroxyapatite can bind to bacteria that are floating around the mouth. It will cause all of them to bind to it rather than the enamel. It is similar to a magnet that attracts all of the bacteria to it and once them bind to it, they become immobilized.
Bacteria will normally attach to the pellicle receptors on the enamel and that is how plaque begins to form. However the nano hydroxyapatite will compete with the bacteria in binding to these receptors. Essentially they hog all of the open receptors thus effectively preventing bacteria from even getting a chance at even forming plaque over the enamel.
Studies do show support for their plaque control capabilities. It seems to be comparable to amine and stannous fluoride toothpaste in reducing plaque and bleeding gums. It seems to be even as effective as an actual antibacterial mouth rinse, chlorhexidine.
Anti-sensitivity
Hydroxyapatite based toothpastes reduce teeth sensitivity by occluding open dentinal tubules. The physical occlusion of the tubules were verified by SEM photos which visually showed blocked off orifices.
The tubular occlusions are effective in decreasing sensitivity because it blocks stimuli from interacting with nerve endings inside the tubules. Patients with dentin hypersensitivity often have open tubules or even enlarged orifices. This is in contrast to those without symptoms who have natural smear plugs that clog the tubules.
Brushing with the hydroxyapatite toothpaste will essentially recreate these smear plugs and close off all the open orifices. The only difference this time around is that these plugs are made of hydroxyapatite which is identical to your tooth structure. That is also why it binds really well to enamel.
Effectiveness of the desensitization
From as early as 1987, a study found that use of a hydroxyapatite toothpaste reduced sensitivity for 90% of participants after 3-5 days. A different study found that it only took 3 days for it to significantly reduce symptoms.
In other words, this works for decreasing teeth sensitivity. In case you were wondering, it is even effective enough to be used for desensitizing teeth after teeth whitening. Sensitive teeth are bad enough as it is on a daily basis but bleaching them can cause an exaggerated response that is incredibly discomforting. Since it works for post-whitening sensitivity, it will definitely work on your everyday symptoms.
Teeth whitening
This mineral in your toothpaste can not only remineralize your teeth and reduce sensitivity but it can also make them appear whiter. However, hydroxyapatite doesn't "whiten" your teeth like hydrogen peroxide does since it doesn't oxidize any stains.
How nanohydroxyapatite whitens your teeth is by turning the surface smoother and glossier. This has to do with how it remineralizes your teeth. Since it is identical in composition to your enamel, it literally inserts itself into demineralized areas and other porosities that may be present. Since it fills in all of the voids, it makes the tooth smoother which is why a lot of patients reported a "smoothness" feeling from using it.
Aside from that, there is also the fact that the natural color of this mineral is white. Since it fills in the missing minerals and it can create a synthetic layer of itself over it, it will make the tooth appear brighter.
Despite this unexpected but welcomed effect of using it, studies have shown that it is nowhere near as effective as peroxide based whitening products. Actual bleaching material seems to be twice as effective as the whitening capability of hydroxyapatite.
Can hydroxyapatite rebuild enamel?
Hydroxyapatite in toothpaste can repair small defects in demineralized enamel but it cannot build new enamel stemming from cavitations. The delineation lies in the severity of the defect in the enamel.
Small defects where the enamel is demineralized is essentially a "pre-cavity" or the beginning stages of one. These lesions often look like white spots on the enamel but there is no clinically perceivable "hole" in the tooth.
These mild deformities can be repaired by the toothpaste since the super structure is mostly intact. There may be mild porosities of demineralized regions within it which can literally be filled in with nano-hydroxyapatite. It is almost akin to filling in a pot hot on asphalt.
Larger defects such as an actual cavitation in the tooth is beyond the capabilities of hydroxyapatite. This is much more than simply filling in small porosities because there is literally a large piece of the tooth missing. Only stem cells can regrow the missing enamel in this case but human technology has not reached that stage yet.
The reason why it cannot rebuild this missing tooth structure is because the hydroxyapatite can only fill in missing spaces. Since this is a big cavitation, it needs guidance as to how it should build out and in what shape it would ultimately become. That requires much more than patching up a hole.
Hydroxyapatite toothpaste side effects
In contrast to other oral care products, hydroxyapatite is highly biocompatible and biomimetic in nature since it is the same mineral that teeth are made of. That is why they're sometimes referred to as synthetic enamel paste. In other words it is non-toxic and non-irritating so it is safe to use on a daily basis in toothpaste.
There have been questions over what happens if you accidentally swallow this while brushing your teeth. Unlike fluoride which can be toxic at higher doses, no harm will befall you from swallowing hydroxyapatite.
In the unlikely situation that you do, the hydroxyapatite will react with stomach acid the same way that it does in an acidic oral environment. This mineral will simply demineralize and dissolve into its individual mineral components, calcium and phosphate.
The equation for demineralization of hydroxyapatite in the presence of acid whether in the mouth or in the stomach is as such: Ca10(PO4)6(OH)2 + 8 H+ → 10 Ca2+ + 6 HPO42- + 2 H2O
Essentially it will break up into calcium, phosphates, and water. These will get reabsorbed once they reach the intestines and then your body can reuse them elsewhere. It may even end up back in your teeth at a later point in time.
Can it cause an allergic reaction?
People can be allergic to many things but hydroxyapatite is not one of them. It is virtually impossible to be allergic to it because the primary mineral in your teeth and bones is made of it. The enamel consists of 97% of it while your bones have around 60% by weight.
If you were allergic to it, your mouth would be perpetually itchy since your lips and tongue rub against your teeth all day long. Basically it is not possible for that to happen. In case you wanted reassurance, studies have shown that there were no allergic reactions to it, including applications of it on your skin.
Additional research also states that hydroxyapatite cannot possess immunotropic or allergenic characteristics. It is due to this reason that it is incredibly biocompatible and considered biomimetic. In other words, it is perfectly safe to use.
Nano-hydroxyapatite vs fluoride for remineralization
Both remineralizing agents, fluoride and hydroxyapatite, have been shown to be comparable in their remineralization efficacy without a statistical difference. Therefore you can feel free to choose whichever one you want to use as your primary toothpaste.
Hydroxyapatite vs Fluoride:
Hydroxyapatite leaves the surface of the enamel smoother. A rough surface attracts more bacteria because they can adhere to it more easily.
Fluoride can form fluorapatite which is more resistant than plain hydroxyapatite. The pH at which the former dissolves is 4.5 while the latter is 5.5 and that is a distinct advantage.
Can you use them together?
Fluoride and nano-hydroxyapatite work via slightly different mechanisms and thus, there has been evidence that their effects may be synergistic.
One study found that using a nano-hydroxyapatite toothpaste with a sodium fluoride mouth rinse was beneficial in remineralizing teeth. A different study tested the combination in combating demineralization around orthodontic brackets. The conclusion was that it did help and it was effective. However more studies are needed to verify these results.
Our dentists in Long Island City have used toothpastes which contained both together without any adverse effects.
