News for dentistry professionals
25 Oct 2019
Hydroxyapatite [Ca10(PO4)6(HO)2] is the third most abundant element in the human body, and the main component of bone and dental tissues. With respect to teeth, it represents 95-97% of the enamel by weight, 70% of that of the dentin and 50-60% of the cementum. Hydroxyapatite makes enamel the hardest part of the human body.
Enamel is basically formed by hydroxyapatite crystals, so compact that the enamel looks like glass, and that is why it is translucent. In fact, the yellowish-white of the teeth is due to the reflection of the dentin through the translucent enamel crystals. In other words, hydroxyapatite influences the colour and appearance of the teeth.
The main function of the enamel is to protect the teeth from external aggressions. Despite being the hardest part of the body, in acidic pH conditions it can become demineralised, especially when it drops below the critical point, i.e. at pH 5.5. The hydroxyapatite begins to demineralise and is dissociated, forming Ca2+, PO4 and OH- ions, which will generally end up in the saliva.
Subsequently, these and other similar ions present in the saliva, supersaturated with calcium and phosphate, in addition to fluoride, can re-enter the enamel during the remineralisation process. The teeth are thus in continuous flux between demineralisation-remineralisation. An imbalance protracted over time tending towards demineralisation will result in the appearance of caries.
Fluoride is the most commonly used element for caries prevention. Its topical application, in the form of fluoride ions, inhibits the demineralisation of enamel and favours its remineralisation. In addition, the combination of fluoride and hydroxyapatite ions results in several compounds, including fluorapatite. Fluorapatite crystals are larger and more resistant to acid dissolution than the original enamel. In fact, the critical point of fluorapatite is one point less than that of hydroxyapatite as it begins demineralising at pH 4.5 instead of pH 5.5.
Thus, hydroxyapatite is a key component in the resistance of teeth to demineralisation, and its combination with fluoride ions helps to form even more resistant compounds, preventing the onset of decay.
Because of several factors, including acid erosion, the enamel layers can wear away, or even totally disappear, as may occur with the cementum if there is recession of the gums. In such cases, the dentin becomes exposed, loses its natural protection, and if the dentinal tubules are open as well as being exposed, this may result in dental hypersensitivity.
The dentin is more organic and contains less hydroxyapatite (70%) than enamel. It is thus less resistant and carious lesions will progress more rapidly in this tissue. Dentin features a natural self-healing process that consists of the formation of a smear layer.
The smear layer is a thin coat that is deposited on the dentin, covering the dentinal tubules and thus prevents external stimuli from affecting the pulp. It is mainly composed of collagen and fragments of hydroxyapatite. In other words, hydroxyapatite acts by helping to prevent dental hypersensitivity. Hydroxyapatite thus has an impact on the appearance of the teeth, on the caries process and on dental hypersensitivity.
Therefore, hydroxyapatite plays a fundamental role in dental health.
The DENTAID Research Center has developed the innovative DENTAID technology haprepair. This exclusive technology is based on the incorporation of active hydroxyapatite, a natural element found in the teeth which is the able to combine with the enamel surface and the exposed dentin.
Topical application of active hydroxyapatite in oral hygiene products provides the following benefits:
• Forms a protective layer on the enamel, and combined with fluoride, helps increase the resistance of the enamel.
• Repairs imperfections in the enamel, providing a smoother, brighter surface and thus a whiter appearance.
• In case of dentin exposure, helps to cover the exposed dentinal tubules by forming a protective layer.
• Constitutes a mineral reservoir for the teeth, especially when pH is low, thus preventing the demineralisation of the enamel.
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