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Written by Kristina Sales-Cuadra
What’s the difference between nano-hydroxyapatite and fluoride, and which one actually remineralizes and strengthens teeth? The answer may surprise you! If you’ve been anywhere on social media recently, you may have seen nano-hydroxyapatite products advertised as the next greatest thing to help rebuild teeth that have cavities in them. They’ll often have a headline that’s something like “Your dentist doesn’t want you to know, but you don’t need fillings to fix your cavities”. Spoiler alert, we very much want you to know how to remineralize teeth! We want you to know so badly, it practically leaks out of our pores during your visits with us. Anyone that advertises that way usually has something they want to sell you, and it’s really easy to make us the scapegoats
The truth is, in both dental and hygiene school, we are trained in strategies to remineralize teeth, and your dentist is actively working to identify cavities early so they can be fixed through any means other than a filling. Anytime we do a restoration, it’s because there’s an actual hole in the tooth, and no amount of remineralization is going to fill that hole: it’s time for a filling or a crown, depending on the extent of structure lost. However, if we can identify a cavity before it’s actually a hole, then our goal is to remineralize that before it needs a filling.
So what actually works? Does nano-hydroxyapatite actually remineralize teeth? Is it even beneficial? Like so many things in this world, the answer is, it’s complicated
So what does toothpaste actually do? Toothpaste is meant to aid in removal of bacterial colonies habitating on the oral surfaces, both soft and hard. Toothpaste was originally implemented to increase patient compliance through gels and pastes that leave the mouth feeling fresh and clean, usually via an essential oil, menthol, which leaves the mouth feeling minty-fresh. Toothpaste also reduces surface staining, clears bacterial plaque (biofilm), and acts as a delivery system for medicaments, such as fluoride or cetylpyridinium chloride (anti-gingivitis product).
The fluoride that is in over the counter toothpaste is relatively low concentration, about .45%, whereas prescription fluoride toothpastes has about twice the concentration, 1.1%. The fluoride in OTC toothpaste is meant to act as prevention, whereas the 1.1% is used for people with high cavity rates, and folks with higher risk (such as a person with dry mouth).
When a patient has diagnosed caries (the disease commonly called cavities), it is recommended that for the next two years, they are treated with topical fluoride varnish for cavity prevention and arrest at a much higher concentration, 5%.; this varnish is applied by your professional dental team. Fluoride can be toxic when ingested, however, it is critical to note that the amount of fluoride being ingested is the qualifier for toxicity, not the chemical itself. Fluoride varnish applied to the teeth hardens and adheres to the tooth so it has greater contact time to strengthen the enamel. A very small volume of varnish is applied to the teeth which is safe for children and adults to ingest at the rate of every 3-6 months, without any toxicity concerns.
So what does fluoride actually do? Fluoride is not capable of remineralizing the tooth structure itself, however, it does interact with the chemicals which do take part in the remineralization process such that fluoride is integrated and can replace existing hydroxyl group components in the enamel, creating a structure (fluorapatite) which has a greater resistance to acid attacks than regular enamel (the strongest substance our body makes). Fluoride being built into the existing tooth structure means that the tooth is stronger structurally in a way that beats the hydroxyl group in enamel in a combat against the acid produced by bacteria in dental plaque.
When nano-hydroxyapatite (NaH) enters the conversation, she turns heads. NaH in in-vitro studies has shown remarkable results in desensitizing and remineralizing enamel. The problems lie just beyond the exits of the lab, and right at the entrance of the mouth: saliva. When NaH, powder or suspensions, come in contact with water and saliva, they clump. The initial research I did about NaH showed that the most important component of choosing the efficacy in a lab for remineralization and desensitization was the particle shape: rod shapes slip into the open dentinal tubules, occluding the surface, preventing transitional vibration which results in dentinal hypersensitivity (that quick zing from cold water, hygiene instruments, or even floss/brushing) – odd shapes and spheres will inefficiently do this and will often fail to occlude any tubules. Because the mouth is a wet exposure to NaH in toothpaste is considered ineffective – the active ingredient clumps to form groups of these -hopefully- rod shaped pieces, which are no longer small enough to fit into the tubules. When tubules are able to be filled by odd pieces of NaH, the particles occlude the tubules, reducing sensitivity, but are not built into the structure, and can easily be lost. This makes NaH possibly a decent product to work on sensitivity, but the evidence shows that the results are likely limited and short term. NaH, especially when clumped in a wet environment, is not able to be processed through our body cells when they are taken up into the soft tissues, which nano-particles are famous for their ability to do. Studies have shown the clumps being targeted by our immune cells, which are unable to process the material, excreting it through the white blood cell membranes after the initial cell fails to break the material down and dies, signalling the immigration of more white blood cells to combat this substance. Because the immune cells are unable to eradicate the built up NaH, the immune system is left in a cyclical pattern of activation, phagocytosis (cells eat the foreign substance), apoptosis (cell death), and further activation and immigration of white blood cells, creating a chronic inflammatory response. Until NaH is further studied and can be proven to go through the system without this risk of inflammatory activation, it would be unethical for our office to suggest the use of products with these ingredients, regardless of their advertised promise.
OK, so how can we actually reverse decay? In modern dental practice, SDF is the only item that shows efficacy and safety for use in chairside cavity treatment (in an office). SDF, or silver diamine-fluoride is a product composed of silver and fluoride ions to provide a topical agent your dentist can place on areas of active decay to arrest or stop the decay in its tracks, as well as strengthening the surrounding tooth structure. SDF, however, does not fill holes made by decay, nor will it leave the tooth white after it’s done its job. SDF is known to leave a blue-black stain on the tooth which is hardened and protected, but many patients don’t find the discoloration acceptable for stopping decay. SDF remains an important cavity-stopping product for dental teams to utilize because it can provide treatment for disease in circumstances where financial hardship may prevent patients from receiving treatment, resulting in potentially dangerous infections to fester.
In the dental world when discussing remineralization we are talking about potentially enhancing or hindering the biological actions of our saliva. Whenever we eat or drink anything other than plain tap water or slightly alkalized drinks, our mouth becomes an acidic environment for up to an hour, assuming our saliva is healthy in quantity and quality. Good quality saliva is slightly thick and slightly watery, clear, and filled with micronutrients such as calcium, phosphorus, bicarbonate, sodium, chlorine, magnesium, and sodium, in addition to proteins and sugars. In a healthy mouth, the saliva is acidic for 30 minutes to 1-hour after meals. When the saliva is acidic, the material making up our enamel, phosphorus, calcium, and hydroxyl-groups are leached from the tooth and suspended in the saliva – this is called demineralization. When that same healthy patient waits 30 minutes after eating, the acid is neutralized, the calcium and phosphorus and hydroxyl-group now are chemically able to bind back to each other, forming hydroxyapatite, which the tooth now takes up in the structure of the tooth – this is called remineralization. When people have poor salivary flow or have poor nutrient density in their saliva, the spit that normally acts as a buffer to neutralize the acid in our mouths after meals fails to protect the teeth from cavity-causing bacterial plaque.
When fluoride is present in the saliva, either from systemic ingestion (water fluoridation) or topical suspension (from toothpaste, rinses, varnish), the calcium and phosphorus bind to the fluoride ion rather than the hydroxyl-group, creating fluorapatite. Fluorapatite is more acid resistant than hydroxyapatite, making it more effective at halting decay.
There have been claims that fluoride and NaH products will reverse decay and build back tooth structure – these claims are false. Fluoride could be argued to remineralize the tooth, creating structure to replace softened enamel – technically, this is untrue because saliva is the catalyst of remineralization, but fluoride can be a supportive partner in stopping and reversing decay, though it will never be sufficient to fill a hole, just harden the surface and reverse the active decay. This is evident when we look at incipient caries, cavities which have not formed a hole but show the enamel is breaking down due to a regular, unmanaged acid attack. When we remove and treat the biofilm causing the decay (applied varnish to an incipient lesion), we are able to stop the active acid attack on the tooth, as well as offering the surround saliva with fluoride which will replace the missing hydroxyapatite that was lost due to the acid. These lesions with dedicated hygiene and good systemic health can harden after a dentist diagnoses decay, but if there is a hole, the hole will need to be filled.
NaH in lab studies shows great success at reversing decay, but without clinical evidence showing that the active ingredient is able to stay stable in wet environments, we can easily find the flaws in these claims. Holes should still be filled to prevent the patient from battling a plaque-retention-factor in their hygiene unnecessarily.
For patients who choose to avoid fluoride can combat decay through meticulous hygiene, a balance diet containing plenty of vegetables and fruits (bicarbonate), calcium rich plants and dairy items, and xylitol rich products (a non-fermentable birch-sugar which neutralizes acid). Something I encourage my patients to do is discuss with their primary care physician whether a vitamin D supplement might be appropriate for you – vitamin D is essential for our body to metabolize calcium, those with deficiencies in vitamin D may not have sufficient blood serum calcium to combat decay.
Other prevention strategies we discuss are topical rinses with calcium (ElementaSilver), more frequent hygiene, and change in lifestyle habits, such as reducing regular snacking, changing out snacks with carbs for snacks with fats and protein, limiting drinking non-water beverages to meal times, and introducing xylitol gums, mints, and rinses after meals to help neutralize the acid from meals.
As you can see, the idea that we can remineralize teeth via nano-hydroxyapatite or fluoride is a complex one and there’s no simple answer. Ultimately any preventative treatment is going to result from a conversation between us and the patient. Any proposed solution will always be tailored to the patient’s lifestyle, goals, and willingness to change. What questions did this bring up for you? Let us know!