Hydroxyapatite is included in toothpaste as a remineralising agent – a compound that promotes the reintegration of calcium and phosphate ions into the tooth. Calcium and phosphate ions are the building blocks of the teeth, and they are required to rebuild your teeth through the natural repair process – remineralisation. Remineralisation keeps your teeth strong and prevents cavities from forming [1]. Hydroxyapatite has recently gained popularity worldwide due to its biocompatibility with the structure of the tooth, its non-toxicity and safety for use in children, and the added benefits of naturally whitening teeth and reducing dentine sensitivity [2,3].
Hydroxyapatite is considered to be biocompatible because it is the same compound that our teeth are made of. Human enamel consists of a proportion of 97% hydroxyapatite crystallites [4], whereas it makes up approximately 70% of the dentine structure [5]. There are two forms of hydroxyapatite that are used in toothpaste, micro and nano, the difference between the two is the size of the crystallites. The hydroxyapatite crystals in the tooth enamel are 20 to 40 nm in size, therefore nano-hydroxyapatite has proved to be highly effective as a remineralising agent due to its structural and chemical similarity to the tooth [6].
Modes of action
There are four main modes of action of hydroxyapatite in enamel remineralization. They are as follows:
Remineralisation booster
There is a reversible chemical reaction that takes place at the tooth surface, this includes demineralisation and remineralisation. Brushing with hydroxyapatite toothpaste has the potential to shift this chemical reaction towards remineralisation by enhancing the levels of calcium and phosphate ions in the saliva [7]. The abundance of calcium and phosphate ions will increase the rate of remineralisation and slow down the rate of demineralisation. These ions also neutralise the pH of the oral cavity further favoring remineralisation [2]. This process aids in mending initial caries lesions [8].
Hydroxyapatite crystallites are also able to bind directly to the enamel crystallites by forming mineral-mineral bridges. Nano-hydroxyapatite is particularly effective at doing this due to its elevated surface energy which promotes the formation of strong bonds [7]. Additionally, due to the small size of nano-hydroxyapatite, it is highly effective at filling initial caries lesions below the surface of the enamel. This is something that fluoride compounds are not able to do.
Calcium Reservoir
After brushing with a hydroxyapatite toothpaste, hydroxyapatite crystallites adhere to the tooth and are stored in the surrounding biofilm [3]. The stored hydroxyapatite crystallites act as a calcium reservoir. Upon exposure to an acidic environment, due to the consumption of acidic foods or production by cariogenic bacteria, these hydroxyapatite crystallites release calcium and phosphate ions. As previously mentioned, these ions favour the rate of remineralisation and slow down the rate of demineralisation. This calcium reservoir can be thought of as an extra precaution aiding in protection against possible acid attacks.
Inhibit bacterial plaque adhesion
It has been found that hydroxyapatite was as effective as a popular anti-microbial, chlorhexidine, at reducing the number of plaque-forming bacteria on the tooth surface. However, this was not due to any anti-microbial mode of action [9]. Hydroxyapatite crystallites become incorporated into the microbial biofilm surrounding the teeth [3]. In doing so, plaque-forming bacteria, perhaps confused by the striking resemblance, adhere to the hydroxyapatite crystallites instead of the enamel. Once these bacteria have bound to the hydroxyapatite crystallites they form aggregates that are easily removed from the oral cavity by saliva. Additionally, by remineralising the enamel surface, gaps are closed creating a smoother surface. This means that there are now fewer grooves and crevices and a smaller surface area for bacteria to attach to [8]. This further reduces the proliferation of plaque-producing bacteria.
Sacrificial protective layer
Hydroxyapatite binds to the tooth surface, in doing so it creates a new layer of enamel that protects the underlying tooth from future acid attacks [2].
These four general modes of action allow hydroxyapatite toothpaste to effectively remineralise enamel, and it has been successfully confirmed by several in vitro [10–12] and human clinical trials [13,14]. This is why EvaGlo has chosen to use nano-hydroxyapatite as an alternative to fluoride.
References
- Li, X.; Wang, J.; Joiner, A.; Chang, J. The remineralisation of enamel: A review of the literature. J. Dent. 2014, 42, S12–S20, doi:10.1016/S0300-5712(14)50003-6.
- Chen, L.; Al-bayatee, S.; Khurshid, Z.; Shavandi, A.; Brunton, P.; Ratnayake, J. Hydroxyapatite in Oral Care Products — A Review. Materials. 2021, 14, 4865–4885.
- Meyer, F.; Enax, J.; Amaechi, B.T.; Limeback, H.; Fabritius, H.; Ganss, B.; Pawinska, M.; Paszynska, E. Hydroxyapatite as Remineralization Agent for Children’ s Dental Care. Front. Dent. Med. 2022, 3, 1–10, doi:10.3389/fdmed.2022.859560.
- Dorozhkin, S. V; Epple, M. Biological and Medical Significance of Calcium Phosphates. Angew. Chem. Int. Ed. 2002, 41, 3130–3146.
- Sarna-Boś, K.; Skic, K.; Boguta, P.; Adamczuk, A.; Vodanovic, M.; Chalas, R. Elemental mapping of human teeth enamel, dentine and cementum in view of their microstructure. Micron 2023, 172, doi:10.1016/j.micron.2023.103485.
- Anil, A.; Ibraheem, W.I.; Meshni, A.A.; Preethanath, R.; Anil, S. Demineralization and Remineralization Dynamics and Dental Caries. In Dental Caries – The Selection of Restoration Methods and Restorative Materials; Rusu, L.-C., Ardelean, L.C., Gehrke, S.A., Eds.; IntechOpen, 2022 ISBN 978-1-80356-360-2.
- Anil, A.; Ibraheem, W.I.; Meshni, A.A.; Preethanath, R.S.; Anil, S. Nano-Hydroxyapatite (nHAp) in the Remineralization of Early Dental Caries: A Scoping Review. Int. J. Environ. Res. Public Heal. 2022, 19, 5629–5643, doi:10.3390/ijerph19095629.
- Grohe, B.; Mittler, S. Advanced non-fluoride approaches to dental enamel remineralization: The next level in enamel repair management. Biomater. Biosyst. 2021, 4, 100029, doi:10.1016/j.bbiosy.2021.100029.
- Kensche, A.; Holder, C.; Basche, S.; Tahan, N.; Hannig, C.; Hannig, M. Archives of Oral Biology Ef fi cacy of a mouthrinse based on hydroxyapatite to reduce initial bacterial colonisation in situ. Arch. Oral Biol. 2017, 80, 18–26, doi:10.1016/j.archoralbio.2017.03.013.
- Kasemkhun, P.; Rirattanapong, P. The Efficacy of Non-Fluoridated Toothpastes on Artificial Enamel Caries in Primary Teeth: An In Vitro Study. J Int Soc Prev Community Dent 2021, 11, 397–401, doi:10.4103/jispcd.JISPCD_64_21.
- Huang, S.; Gao, S.; Cheng, L.; Yu, H. Remineralization potential of nano-hydroxyapatite on initial enamel lesions: An in vitro study. Caries Res. 2011, 45, 460–468, doi:10.1159/000331207.
- Paszynska, E.; Pawinska, M.; Enax, J.; Meyer, F.; Schulze zur Wiesche, E.; May, T.W.; Amaechi, B.T.; Limeback, H.; Hernik, A.; Otulakowska-Skrzynska, J.; et al. Caries-Preventing Effect of a Hydroxyapatite-Toothpaste in Adults: A 18-Month Double-Blinded Randomized Clinical Trial. Front Public Health 2023, 11, doi:10.3389/fpubh.2023.1199728.
- Grocholewicz, K.; Cichocka, G.M.; Makowiecki, P.; Droździk, A.; Chmielewska, H.E.; Dziewulska, A.; Tomasik, M. Effect of nano ‑ hydroxyapatite and ozone on approximal initial caries : a randomized clinical trial. Sci. Rep. 2020, 1–8, doi:10.1038/s41598-020-67885-8.
- Badiee, M.; Jafari, N.; Fatemi, S.; Ameli, N.; Kasraei, S.; Ebadifar, A. of the effects of toothpastes containing nanohydroxyapatite and fluoride on white spot lesions in orthodontic patients : A randomized clinical trial. Dent. Res. J. 2020, 17, 354–359.
