Amorphous calcium phosphate
This article may be too technical for most readers to understand.(July 2017) |
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]
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
Biogenic ACP
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
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
References
External links
- Mahamid, J.; Aichmayer, B.; Shimoni, E.; Ziblat, R.; Li, C.; Siegel, S.; Paris, O.; Fratzl, P.; Weiner, S.; Addadi, L. (2010). "Mapping amorphous calcium phosphate transformation into crystalline mineral from the cell to the bone in zebrafish fin rays". Proc. Natl. Acad. Sci. U.S.A. 107 (14): 6316–21. PMID 20308589.
- Zhao, J.; Liu, Y.; Sun, W. B.; Zhang, H. (2011). "Amorphous calcium phosphate and its application in dentistry". Chem. Cent. J. 5: 40. PMID 21740535.
- Ming S. Tung. "ACP Technology. Amorphous Calcium Phosphate forming Fluoride Varnishes" (PDF). American Dental Association. Archived from the original (PDF) on 2013-01-25.