Amorphous calcium phosphate

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Amorphous calcium phosphate (ACP) is a glassy solid that is formed from the chemical decomposition of a mixture of dissolved phosphate and calcium salts (e.g. (NH4)2HPO4 + Ca(NO3)2). The resulting amorphous mixture consists mostly of calcium and phosphate, but also contains varying amounts of water and hydrogen and hydroxide ions, depending on the synthesis conditions. [1] Such mixtures are also known as calcium phosphate cement. [2]

Contents

ACP is generally categorized into either "amorphous tricalcium phosphate" (ATCP) or calcium-deficient hydroxyapatite (CDHA). CDHA is sometimes termed "apatitic calcium triphosphate." [1] [3] [4] The composition of amorphous calcium phosphate is CaxHy(PO4)z·nH2O, where n is between 3 and 4.5. CDHA has a general formula of Ca9(HPO4)(PO4)5(OH). [4] Precipitation from a moderately supersaturated and basic solution of a magnesium salt produces amorphous magnesium calcium phosphate (AMCP), in which magnesium incorporated into the ACP structure. [5]

A commercial preparation of ACP is casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), derived from cow milk. It is sold under various brand names including Recaldent and Tooth Mousse, intended to be applied directly to teeth. Its clinical usefulness is unproven. [6]

Biogenic ACP

Biogenic ACP has been found in the inner ear of embryonic sharks, mammalian milk and dental enamel. However, whilst its unequivocal presence in bones and teeth is debated, there is evidence that transient amorphous precursors are involved in the development of bone and teeth. [4] The ACP in bovine milk (CPP-ACP) is believed to involve calcium phosphate nanoclusters in a shell of casein phosphopeptides. A typical casein micelle of radius 100 nm contains around 10,000 casein molecules and 800 nanoclusters of ACP, each about 4.8 nm in diameter. The concentration of calcium phosphate is higher in milk than in serum, but it rarely forms deposits of insoluble phosphates. [7] Unfolded phosphopeptides are believed to sequester ACP nanoclusters [8] and form stable complexes in other biofluids such as urine and blood serum, preventing deposition of insoluble calcium phosphates and calcification of soft tissue. In the laboratory, stored samples of formulations of artificial blood, serum, urine and milk (which approximate the pH of the naturally occurring fluid) deposit insoluble phosphates. The addition of suitable phosphopeptides prevents precipitation. [7]

Posner's clusters

Following investigations into the composition of amorphous calcium phosphates precipitated under different conditions, Posner and Betts suggested in the mid-1970s that the structural unit of ACP was a neutral cluster Ca9(PO4)6. [4] Calculations support the description of a cluster with central Ca2+ ion surrounded by six phosphate PO43− anions, which in turn are surrounded by eight further calcium ions. [9] The resulting cluster is estimated to have a diameter of around 950 pm (0.95 nm). These are now generally referred to as Posner's clusters. Precipitated ACP is believed to be made up of particles containing a number of Posner's clusters with water in the intervening spaces. While plasma spray coated ACP may contain Posner's clusters, there cannot be any water present. [4] New studies propose the idea of posner clusters acting as neural qbits because their entangled 31P have a long relaxation time and are in a S6 symmetry. The idea behind it is that the posner molecules meld and release calcium-ions which stimulises the neurons. [10]

Use in dental treatment

Amorphous calcium phosphate in combination with casein phosphopeptide has been used as a dental treatment to treat incipient dental decay. ACP sees its main use as an occluding agent, which aids in reducing sensitivity. Studies have shown that it does form a remineralized phase of hydroxyapatite consistent with the natural enamel.[ citation needed ] In addition, clinical studies have shown that patients who whiten their teeth have reduced sensitivity after treatment. [11] It is believed that ACP hydrolyzes under physiological temperatures and pH to form octacalcium phosphate as an intermediate, and then surface apatite.[ citation needed ]

Method of mineralization

ACP lacks the long-range, periodic atomic-scale order of crystalline calcium phosphates. The X-ray diffraction pattern is broad and diffuse with a maximum at , and no other different features compared with well-crystallized hydroxyapatite. Under electron microscopy, its morphological form is shown as small spheroidal particles in the scale of tenths nanometer. In aqueous media, ACP is easily transformed into crystalline phases such as octacalcium phosphate and apatite due to the growing of microcrystallites. It has been demonstrated that ACP has better osteoconductivity and biodegradability than tricalcium phosphate and hydroxyapatite in vivo. [12]

Moreover, it can increase alkaline phosphatase activities of mesoblasts, enhance cell proliferation and promote cell adhesion. The unique role of ACP during the formation of mineralized tissues makes it a promising candidate material for tissue repair and regeneration. ACP may also be a potential remineralizing agent in dental applications. Recently developed ACP-filled bioactive composites are believed to be effective anti-demineralizing/remineralizing agents for the preservation and repair of tooth structures. [12]

See also

Related Research Articles

<span class="mw-page-title-main">Casein</span> Family of proteins found in milk

Casein is a family of related phosphoproteins that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in human milk. Sheep and cow milk have a higher casein content than other types of milk with human milk having a particularly low casein content.

<span class="mw-page-title-main">Apatite</span> Mineral group, calcium phosphate

Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ion, respectively, in the crystal. The formula of the admixture of the three most common endmembers is written as Ca10(PO4)6(OH,F,Cl)2, and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6F2 and Ca10(PO4)6Cl2.

<span class="mw-page-title-main">Toothpaste</span> Substance to clean and maintain teeth

Toothpaste is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from the teeth, assists in suppressing halitosis, and delivers active ingredients to help prevent tooth decay and gum disease (gingivitis). Owing to differences in composition and fluoride content, not all toothpastes are equally effective in maintaining oral health. The decline of tooth decay during the 20th century has been attributed to the introduction and regular use of fluoride-containing toothpastes worldwide. Large amounts of swallowed toothpaste can be poisonous. Common colors for toothpaste include white and blue.

<span class="mw-page-title-main">Calculus (dental)</span> Form of hardened dental plaque

In dentistry, calculus or tartar is a form of hardened dental plaque. It is caused by precipitation of minerals from saliva and gingival crevicular fluid (GCF) in plaque on the teeth. This process of precipitation kills the bacterial cells within dental plaque, but the rough and hardened surface that is formed provides an ideal surface for further plaque formation. This leads to calculus buildup, which compromises the health of the gingiva (gums). Calculus can form both along the gumline, where it is referred to as supragingival, and within the narrow sulcus that exists between the teeth and the gingiva, where it is referred to as subgingival.

<span class="mw-page-title-main">Tooth enamel</span> Major tissue that makes up part of the tooth in humans and many animals

Tooth enamel is one of the four major tissues that make up the tooth in humans and many animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, cementum, and dental pulp. It is a very hard, white to off-white, highly mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation, especially by acids from food and drink. In rare circumstances enamel fails to form, leaving the underlying dentin exposed on the surface.

<span class="mw-page-title-main">Ultrastructure</span>

Ultrastructure is the architecture of cells and biomaterials that is visible at higher magnifications than found on a standard optical light microscope. This traditionally meant the resolution and magnification range of a conventional transmission electron microscope (TEM) when viewing biological specimens such as cells, tissue, or organs. Ultrastructure can also be viewed with scanning electron microscopy and super-resolution microscopy, although TEM is a standard histology technique for viewing ultrastructure. Such cellular structures as organelles, which allow the cell to function properly within its specified environment, can be examined at the ultrastructural level.

<span class="mw-page-title-main">Calcium phosphate</span> Chemical compound

The term calcium phosphate refers to a family of materials and minerals containing calcium ions (Ca2+) together with inorganic phosphate anions. Some so-called calcium phosphates contain oxide and hydroxide as well. Calcium phosphates are white solids of nutritional value and are found in many living organisms, e.g., bone mineral and tooth enamel. In milk, it exists in a colloidal form in micelles bound to casein protein with magnesium, zinc, and citrate–collectively referred to as colloidal calcium phosphate (CCP). Various calcium phosphate minerals are used in the production of phosphoric acid and fertilizers. Overuse of certain forms of calcium phosphate can lead to nutrient-containing surface runoff and subsequent adverse effects upon receiving waters such as algal blooms and eutrophication (over-enrichment with nutrients and minerals).

<span class="mw-page-title-main">Hydroxyapatite</span> Naturally occurring mineral form of calcium apatite

Hydroxyapatite is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), often written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. It is the hydroxyl endmember of the complex apatite group. The OH− ion can be replaced by fluoride or chloride, producing fluorapatite or chlorapatite. It crystallizes in the hexagonal crystal system. Pure hydroxyapatite powder is white. Naturally occurring apatites can, however, also have brown, yellow, or green colorations, comparable to the discolorations of dental fluorosis.

<span class="mw-page-title-main">Fluoride therapy</span> Medical use of fluoride

Fluoride therapy is the use of fluoride for medical purposes. Fluoride supplements are recommended to prevent tooth decay in children older than six months in areas where the drinking water is low in fluoride. It is typically used as a liquid, pill, or paste by mouth. Fluoride has also been used to treat a number of bone diseases.

<span class="mw-page-title-main">Tricalcium phosphate</span> Chemical compound

Tricalcium phosphate (sometimes abbreviated TCP), more commonly known as Calcium phosphate, is a calcium salt of phosphoric acid with the chemical formula Ca3(PO4)2. It is also known as tribasic calcium phosphate and bone phosphate of lime (BPL). It is a white solid of low solubility. Most commercial samples of "tricalcium phosphate" are in fact hydroxyapatite.

<span class="mw-page-title-main">Dicalcium phosphate</span> Chemical compound

Dicalcium phosphate is the calcium phosphate with the formula CaHPO4 and its dihydrate. The "di" prefix in the common name arises because the formation of the HPO42– anion involves the removal of two protons from phosphoric acid, H3PO4. It is also known as dibasic calcium phosphate or calcium monohydrogen phosphate. Dicalcium phosphate is used as a food additive, it is found in some toothpastes as a polishing agent and is a biomaterial.

<span class="mw-page-title-main">Remineralisation of teeth</span>

Tooth remineralization is the natural repair process for non-cavitated tooth lesions, in which calcium, phosphate and sometimes fluoride ions are deposited into crystal voids in demineralised enamel. Remineralization can contribute towards restoring strength and function within tooth structure.

<span class="mw-page-title-main">Bioceramic</span> Type of ceramic materials that are biocompatible

Bioceramics and bioglasses are ceramic materials that are biocompatible. Bioceramics are an important subset of biomaterials. Bioceramics range in biocompatibility from the ceramic oxides, which are inert in the body, to the other extreme of resorbable materials, which are eventually replaced by the body after they have assisted repair. Bioceramics are used in many types of medical procedures. Bioceramics are typically used as rigid materials in surgical implants, though some bioceramics are flexible. The ceramic materials used are not the same as porcelain type ceramic materials. Rather, bioceramics are closely related to either the body's own materials or are extremely durable metal oxides.

<span class="mw-page-title-main">Mineralized tissues</span> Biological tissues incorporating minerals

Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Typically these tissues form a protective shield or structural support. Bone, mollusc shells, deep sea sponge Euplectella species, radiolarians, diatoms, antler bone, tendon, cartilage, tooth enamel and dentin are some examples of mineralized tissues.

Octacalcium phosphate (sometimes referred to as OCP) is a form of calcium phosphate with formula Ca8H2(PO4)6·5H2O. OCP may be a precursor to tooth enamel, dentine, and bones. OCP is a precursor of hydroxyapatite (HA), an inorganic biomineral that is important in bone growth. OCP has garnered lots of attention due to its inherent biocompatibility. While OCP exhibits good properties in terms of bone growth, very stringent synthesis requirements make it difficult for mass productions, but nevertheless has shown promise not only in-vitro, but also in in-vivo clinical case studies.

A simulated body fluid (SBF) is a solution with an ion concentration close to that of human blood plasma, kept under mild conditions of pH and identical physiological temperature. SBF was first introduced by Kokubo et al. in order to evaluate the changes on a surface of a bioactive glass ceramic. Later, cell culture media, in combination with some methodologies adopted in cell culture, were proposed as an alternative to conventional SBF in assessing the bioactivity of materials.

<span class="mw-page-title-main">Pulp capping</span>

Pulp capping is a technique used in dental restorations to prevent the dental pulp from necrosis, after being exposed, or nearly exposed during a cavity preparation, from a traumatic injury, or by a deep cavity that reaches the center of the tooth causing the pulp to die. When dental caries is removed from a tooth, all or most of the infected and softened enamel and dentin are removed. This can lead to the pulp of the tooth either being exposed or nearly exposed which causes pulpitis (inflammation). Pulpitis, in turn, can become irreversible, leading to pain and pulp necrosis, and necessitating either root canal treatment or extraction. The ultimate goal of pulp capping or stepwise caries removal is to protect a healthy dental pulp and avoid the need for root canal therapy.

Tetracalcium phosphate is the compound Ca4(PO4)2O, (4CaO·P2O5). It is the most basic of the calcium phosphates, and has a Ca/P ratio of 2, making it the most phosphorus poor phosphate. It is found as the mineral hilgenstockite, which is formed in industrial phosphate rich slag (called "Thomas slag"). This slag was used as a fertiliser due to the higher solubility of tetracalcium phosphate relative to apatite minerals. Tetracalcium phosphate is a component in some calcium phosphate cements that have medical applications.

<span class="mw-page-title-main">Molar incisor hypomineralisation</span> Medical condition

Molar incisor hypomineralisation (MIH) is a type of enamel defect affecting, as the name suggests, the first molars and incisors in the permanent dentition. MIH is considered a worldwide problem with a global prevalence of 12.9% and is usually identified in children under 10 years old. This developmental condition is caused by the lack of mineralisation of enamel during its maturation phase, due to interruption to the function of ameloblasts. Peri- and post-natal factors including premature birth, certain medical conditions, fever and antibiotic use have been found to be associated with development of MIH. Recent studies have suggested the role of genetics and/or epigenetic changes to be contributors of MIH development. However, further studies on the aetiology of MIH are required because it is believed to be multifactorial.

Topical fluorides are fluoride-containing drugs indicated in prevention and treatment of dental caries, particularly in children's primary dentitions. The dental-protecting property of topical fluoride can be attributed to multiple mechanisms of action, including the promotion of remineralization of decalcified enamel, the inhibition of the cariogenic microbial metabolism in dental plaque and the increase of tooth resistance to acid dissolution. Topical fluoride is available in a variety of dose forms, for example, toothpaste, mouth rinses, varnish and silver diamine solution. These dosage forms possess different absorption mechanisms and consist of different active ingredients. Common active ingredients include sodium fluoride, stannous fluoride, silver diamine fluoride. These ingredients account for different pharmacokinetic profiles, thereby having varied dosing regimes and therapeutic effects. A minority of individuals may experience certain adverse effects, including dermatological irritation, hypersensitivity reactions, neurotoxicity and dental fluorosis. In severe cases, fluoride overdose may lead to acute toxicity. While topical fluoride is effective in preventing dental caries, it should be used with caution in specific situations to avoid undesired side effects.

References

  1. 1 2 Destainville, A.; Champion, E.; Bernache-Assollant, D.; Laborde, E. (April 2003). "Synthesis, characterization and thermal behavior of apatitic tricalcium phosphate". Materials Chemistry and Physics. 80 (1): 269–277. doi:10.1016/S0254-0584(02)00466-2.
  2. ↑ Al-Sanabani, JS; Madfa, AA; Al-Sanabani, FA (2013). "Application of calcium phosphate materials in dentistry". International Journal of Biomaterials. 2013: 876132. doi: 10.1155/2013/876132 . PMC   3710628 . PMID   23878541.
  3. ↑ Rey, C.; Combes, C.; Drouet, C.; Grossin, D. (2011). "Bioactive Ceramics: Physical Chemistry". Comprehensive Biomaterials. pp. 187–221. doi:10.1016/B978-0-08-055294-1.00178-1. ISBN   978-0-08-055294-1.
  4. 1 2 3 4 5 Dorozhkin, Sergey V. (December 2010). "Amorphous calcium (ortho)phosphates". Acta Biomaterialia. 6 (12): 4457–4475. doi:10.1016/j.actbio.2010.06.031. PMID   20609395.
  5. ↑ Babaie, Elham; Zhou, Huan; Lin, Boren; Bhaduri, Sarit B. (August 2015). "Influence of ethanol content in the precipitation medium on the composition, structure and reactivity of magnesium–calcium phosphate". Materials Science and Engineering: C. 53: 204–211. doi: 10.1016/j.msec.2015.04.011 . PMID   26042708.
  6. ↑ Hani, Thikrayat Bani; O'Connell, Anne C.; Duane, Brett (24 June 2016). "Casein phosphopeptide-amorphous calcium phosphate products in caries prevention". Evidence-Based Dentistry. 17 (2): 46–47. doi: 10.1038/sj.ebd.6401168 . PMID   27339237.
  7. 1 2 Holt, Carl (June 2013). "Unfolded phosphopolypeptides enable soft and hard tissues to coexist in the same organism with relative ease". Current Opinion in Structural Biology. 23 (3): 420–425. doi:10.1016/j.sbi.2013.02.010. PMID   23622834.
  8. ↑ Holt, Carl; Sørensen, Esben S.; Clegg, Roger A. (2009). "Role of calcium phosphate nanoclusters in the control of calcification". FEBS Journal. 276 (8): 2308–2323. doi: 10.1111/j.1742-4658.2009.06958.x . ISSN   1742-464X. PMID   19292864.
  9. ↑ Kanzaki, Noriko; Treboux, Gabin; Onuma, Kazuo; Tsutsumi, Sadao; Ito, Atsuo (November 2001). "Calcium phosphate clusters". Biomaterials. 22 (21): 2921–2929. doi:10.1016/s0142-9612(01)00039-4. PMID   11561898.
  10. ↑ Swift, Michael; Fischer, Mathew; van de Walle, Chris (2018). "Posner molecules: From atomic structure to nuclear spins". Nature. 20 (18): 12373–12380. arXiv: 1711.05899 . Bibcode:2018PCCP...2012373S. doi:10.1039/C7CP07720C. PMID   29379925. S2CID   3212404.
  11. ↑ Van Haywood, B (2002). "Dentine hypersensitivity: bleaching and restorative considerations for successful management". International Dental Journal. 52 (5): 376–384. doi: 10.1002/j.1875-595x.2002.tb00937.x . S2CID   72558772.
  12. 1 2 Zhao, Jie; Liu, Yu; Sun, Wei-bin; Zhang, Hai (December 2011). "Amorphous calcium phosphate and its application in dentistry". Chemistry Central Journal. 5 (1): 40. doi: 10.1186/1752-153X-5-40 . PMC   3143077 . PMID   21740535.
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