You may have heard about hydroxyapatite, but did you know that two forms may be utilised in toothpaste? That is micro and nano-hydroxyapatite, the difference between the two is the size of the hydroxyapatite particles. Micro hydroxyapatite has larger particles in the range of 5-10 microns, whereas nano-hydroxyapatite particles are smaller in the range of 20-100 nm [1]. Both micro and nano-hydroxyapatite are capable of remineralisation of the teeth, however, there are some differences in their capabilities. View the table below to see a summary of the differences between micro and nano-hydroxyapatite.
Micro | Nano | |
Remineralisation (restoring tooth minerals) | Strong affinity and absorption to tooth surfaces [2]. Limited capacity to deliver calcium and phosphate ions into the lesion [3]. Fills micropores in the enamel [2]. Tends to form irregular bodies on the enamel surface [3]. Does not promote remineralization under neutral pH conditions [3]. | Due to smaller particle size, has an even stronger tendency to absorb to the tooth [4]. Better source of free calcium ions which is required for remineralisation [3]. Fill small micro-sized scratches and pits in the enamel [5] Forms a new homogenous surface layer [3]. Promotes remineralization even under neutral pH conditions [3]. |
Microhardness recovery | More effective than micro-Ha [3]. At 10% inclusion level, was as effective as 2200ppm sodium monofluoride [6]. | |
Inhibiting initial caries lesions | At 10% inclusion level: It was as effective as 500 ppm Amine Flouride [2] and 350ppm AMF + 1050 ppm stannous fluoride [7]. | At 10% inclusion level: Was even more effective than 2200 ppm sodium monofluoride [6]. |
Biofilm management | Potential to adsorb to the bacterial cell wall [2] and prevent bacterial attachment to the tooth surface [8]. | Enhanced interaction with bacterial cell walls due to smaller size and greater surface area. Even better at biofilm management [1]. |
Dentine hypersensitivity | Not small enough to occlude open dentine tubules. Cannot reduce fluid flow or block pain signals. | Effective for the relief of dentine hypersensitivity [9]. Due to nano size, can occlude open dentine tubules [10]. Reduces fluid flow in the tubules and blocks pain signals [10]. |
Safety
The research suggests that nano-hydroxyapatite is more effective than micro-hydroxyapatite. However, some people may choose to use micro-hydroxyapatite because they have a negative association with nano-sized particles. It is true that some nanoparticles, like those from pollution or certain industrial processes, have been linked to negative health effects. However, there are also nanoparticles that are applied as beneficial tools in the fields of medicine, water treatment and environmental remediation [11]. Let’s evaluate the literature to determine the safety of nano-hydroxyapatite in toothpaste.
Studies to determine the safety of n-Ha in toothpaste have conducted tests to determine if n-Ha particles are irritating or harmful to human cells. This encompassed analysis to see if n-Ha particles kill human cells altogether, or if there might be any hidden damage to human cells that might affect how well they grow and function. None of the tests showed any negative effects of n-Ha on the measured parameters, indicating that n-Ha particles are cyto-compatible and safe for use in the oral cavity [12,13]. It has also been found that in case the toothpaste is swallowed, there is no risk of absorption of n-Ha particles in the intestines. This is because the n-Ha particles dissolve instantaneously in the stomach acid to form calcium and phosphate ions [14].
In addition to these findings in scientific literature, the Scientific Committee of Consumer Safety (the regulatory body of the European Union), has extensively evaluated the use of n-Ha in toothpaste. To date they have found that n-Ha is safe to use in toothpaste, however, they have set the following regulations for its use (EvaGlo’s nano-hydroxyapatite meets these requirements):
- Maximum Concentration: Up to 10% of the total toothpaste formulation can include n-Ha.
- Rod-shaped particles: At least 95.8% (in particle number) of the n-Ha particles should have an aspect ratio (length to width) less than 3. The remaining 4.2% can have an aspect ratio up to 4.9.
- Non-coated or surface-modified: The n-Ha particles should not be treated with any additional coatings or surface modifications.
In conclusion, both micro and nano-hydroxyapatite can strengthen teeth by remineralising enamel. However, n-Ha offers several advantages: superior remineralisation, enhanced enamel microhardness recovery, improved biofilm management and relief of dentine sensitivity. Studies show no cytotoxicity (harm to cells) and no risk of intestinal absorption if accidentally swallowed. Additionally, the European Union’s Scientific Committee of Consumer Safety has approved n-Ha for use in toothpaste with specific regulations regarding concentration, particle shape, and surface modifications. Based on these findings, EvaGlo has chosen to utilise n-Ha to create a toothpaste that is both effective and safe to use.
References
- 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.
- Amaechi, B.T.; AbdulAzees, P.A.; Alshareif, D.O.; Shehata, M.A.; Lima, P.P. de C.S.; Abdollahi, A.; Kalkhorani, P.S.; Evans, V. Comparative efficacy of a hydroxyapatite and a fluoride toothpaste for prevention and remineralization of dental caries in children. BDJ Open 2019, 5, doi:10.1038/s41405-019-0026-8.
- 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.
- 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.
- Roveri, N.; Battistella, E.; Bianchi, C.L.; Foltran, I.; Foresti, E.; Iafisco, M.; Lelli, M.; Naldoni, A.; Palazzo, B.; Rimondini, L. Surface Enamel Remineralization : Biomimetic Apatite Nanocrystals and Fluoride Ions Different Effects. 2009, 2009, doi:10.1155/2009/746383.
- Juntavee, A.; Juntavee, N.; Sinagpulo, A.N. Nano-Hydroxyapatite Gel and Its Effects on Remineralization of Artificial Carious Lesions. Int. J. Dent. 2021, 2021, doi:10.1155/2021/7256056.
- Schlagenhauf, U.; Kunzelmann, K.H.; Hannig, C.; May, T.W.; Hösl, H.; Gratza, M.; Viergutz, G.; Nazet, M.; Schamberger, S.; Proff, P. Impact of a non-fluoridated microcrystalline hydroxyapatite dentifrice on enamel caries progression in highly caries-susceptible orthodontic patients: A randomized, controlled 6-month trial. J. Investig. Clin. Dent. 2019, 10, e12399, doi:10.1111/jicd.12399.
- 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.
- Melo, C. De; Lucy, B.; Paula, F. De; Ivette, M.; Ortiz, G.; Baraúna, M.; Martins, C.; Cople, L. Clinical e ffi cacy of nano-hydroxyapatite in dentin hypersensitivity : A systematic review and meta-analysis. 2019, 82, 11–21, doi:10.1016/j.jdent.2018.12.014.
- Limeback, H.; Enax, J.; Meyer, F. Clinical Evidence of Biomimetic Hydroxyapatite in Oral Care Products for Reducing Dentin Hypersensitivity : An Updated Systematic Review and Meta-Analysis. 2023.
- Kumah, E.A.; Fopa, R.D.; Harati, S.; Boadu, P.; Zohoori, F. V.; Pak, T. Human and environmental impacts of nanoparticles: a scoping review of the current literature. BMC Public Health 2023, 23, doi:/10.1186/s12889-023-15958-4.
- Coelho, C.C.; Grenho, L.; Gomes, P.S.; Quadros, P.A.; Fernandes, M.H. Nano-hydroxyapatite in oral care cosmetics: characterization and cytotoxicity assessment. Sci. Rep. 2019, 9, 1–10, doi:10.1038/s41598-019-47491-z.
- Kavasi, R.; Coelho, C.C.; Platania, V.; Quadros, P.A.; Chatzinikolaidou, M. In Vitro Biocompatibility Assessment of Nano-Hydroxyapatite. Nanomaterials 2021, 11, doi:/10.3390/nano11051152.
- Ramis, J.M.; Coelho, C.C.; Córdoba, A.; Quadros, P.A.; Monjo, M. Safety Assessment of Nano-Hydroxyapatite as an Oral Care Ingredient according to the EU Cosmetics Regulation. Cosmetics 2018, 5, doi:/10.3390/cosmetics5030053.
