Octacalcium phosphate
Encyclopedia
Octacalcium phosphate (sometimes referred to as OCP) is a calcium
phosphate
with a formula Ca8H2(PO4)6.5H2O. OCP may be a precursor in creation of the tooth enamel
, dentine and bone
s in living organisms.
OCP has been shown to be a precursor of hydroxylapatite
(HAP), an inorganic biomineral that is very important in bone growth. Determinations of the crystal structures of OCP and acidic apatite
thus appear to be a pre-requisite to an understanding of the formation and chemical properties of skeletal tissues. OCP could one day replace HAP
in bone grafts and implants because of the similar apatite structure. OCP is an intermediate complex before the synthesis of HAP
. When mixed with boiling water the crystal structure morphs to one that is very similar to apatitic structure of HAP
. OCP has similar domains to HAP
and has an apatite crystal structure. This makes it ideal to fill in calcium pores in teeth and bones. The morphology of tooth and bone crystallites, as seen in their micrographs, strongly indicates that OCP is involved in the formation of these tissues. There have been studies that have shown the advantages of using OCP in tooth enamel
repair to stimulate the regrowth of the enamel because the crystal structure fits into the pores of tooth enamel
. Studies have been done with titanium plates and bone implants with a coating of OCP. The implants and plates with coatings of OCP were accepted and integrated more quickly and fully than those without OCP because of the apatite crystal structure of OCP that is similar to the crystal structure of bone. OCP shows very promising signs of replacing HAP in bone and tooth repair and growth in grafts and implants and will likely be used more widespread in the healthcare fields.
measurements on OCP gave the lattice a = 19.7 A., b = 9.59 A., c =6.87 A., α≅β = 90.7’ and γ = 71.8’. Corresponding hydroxyapatite constant 2a = 18.84 A., a’ = 9.42 A., c = 6.885 k., α = α’ = 90” and γ = 60”, resemble closely those of OCP in the values of b, c and a, which lie in the plane of the OCP plates. The final pattern was apatitic, intermediate in sharpness between those of tooth enamel and bone. Boiling water decomposed OCP into an apatite approaching hydroxyapatite in composition, along with a variable amount of CaHP04. Both thermal and hydrothermal treatments sometimes yielded apatitic single crystal pseudomorphs after OCP, the c-axes being parallel to the c of the original OCP. Due to the small crystal structure of OCP it is often a twinned crystal structure. The average crystal size of OCP is 13.5 ± 0.2 nm
Dropwise addition of calcium acetate
solution into a sodium acid phosphate solution at pH 5 or 6, maintained at 60°C for 3 to 4 hours.
Ca(C2H3O2)2 + Na2H2P2O7 → Ca4HO12P3 pH 5 or 6
Dropwise addition of calcium acetate
solution into a sodium acid phosphate solution at pH 5 or 6, maintained at 60°C for 3 to 4 hours.
Dropwise addition of calcium into phosphate solution or vice versa at pH 4.5 at 70°C for 1 hour. The solutions were either stirred or unstirred during precipitation and during the subsequent digestion periods. The precipitates are filtered, washed several times with distilled water and air-dried.
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
with a formula Ca8H2(PO4)6.5H2O. OCP may be a precursor in creation of the tooth enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
, dentine and bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s in living organisms.
OCP has been shown to be a precursor of hydroxylapatite
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
(HAP), an inorganic biomineral that is very important in bone growth. Determinations of the crystal structures of OCP and acidic apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
thus appear to be a pre-requisite to an understanding of the formation and chemical properties of skeletal tissues. OCP could one day replace HAP
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
in bone grafts and implants because of the similar apatite structure. OCP is an intermediate complex before the synthesis of HAP
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
. When mixed with boiling water the crystal structure morphs to one that is very similar to apatitic structure of HAP
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
. OCP has similar domains to HAP
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
and has an apatite crystal structure. This makes it ideal to fill in calcium pores in teeth and bones. The morphology of tooth and bone crystallites, as seen in their micrographs, strongly indicates that OCP is involved in the formation of these tissues. There have been studies that have shown the advantages of using OCP in tooth enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
repair to stimulate the regrowth of the enamel because the crystal structure fits into the pores of tooth enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
. Studies have been done with titanium plates and bone implants with a coating of OCP. The implants and plates with coatings of OCP were accepted and integrated more quickly and fully than those without OCP because of the apatite crystal structure of OCP that is similar to the crystal structure of bone. OCP shows very promising signs of replacing HAP in bone and tooth repair and growth in grafts and implants and will likely be used more widespread in the healthcare fields.
Molecular and Crystal Structure
WeissenbergWeissenberg
Weissenberg may refer to:*Weißenberg, a town in Saxony, Germany*the scene of the Battle of White Mountain*Karl Weissenberg , German physicist and founding rheologist, after whom the Weissenberg effect was named...
measurements on OCP gave the lattice a = 19.7 A., b = 9.59 A., c =6.87 A., α≅β = 90.7’ and γ = 71.8’. Corresponding hydroxyapatite constant 2a = 18.84 A., a’ = 9.42 A., c = 6.885 k., α = α’ = 90” and γ = 60”, resemble closely those of OCP in the values of b, c and a, which lie in the plane of the OCP plates. The final pattern was apatitic, intermediate in sharpness between those of tooth enamel and bone. Boiling water decomposed OCP into an apatite approaching hydroxyapatite in composition, along with a variable amount of CaHP04. Both thermal and hydrothermal treatments sometimes yielded apatitic single crystal pseudomorphs after OCP, the c-axes being parallel to the c of the original OCP. Due to the small crystal structure of OCP it is often a twinned crystal structure. The average crystal size of OCP is 13.5 ± 0.2 nm
Synthesis
Ca(CH3COO) + Na2HPO4 + NaH2PO4 → Ca4HO12P3 at pH 5Dropwise addition of calcium acetate
Calcium acetate
The chemical compound calcium acetate is the calcium salt of acetic acid. It has the formula Ca2. Its standard name is calcium acetate, while calcium ethanoate is the systematic IUPAC name. An older name is acetate of lime...
solution into a sodium acid phosphate solution at pH 5 or 6, maintained at 60°C for 3 to 4 hours.
Ca(C2H3O2)2 + Na2H2P2O7 → Ca4HO12P3 pH 5 or 6
Dropwise addition of calcium acetate
Calcium acetate
The chemical compound calcium acetate is the calcium salt of acetic acid. It has the formula Ca2. Its standard name is calcium acetate, while calcium ethanoate is the systematic IUPAC name. An older name is acetate of lime...
solution into a sodium acid phosphate solution at pH 5 or 6, maintained at 60°C for 3 to 4 hours.
Dropwise addition of calcium into phosphate solution or vice versa at pH 4.5 at 70°C for 1 hour. The solutions were either stirred or unstirred during precipitation and during the subsequent digestion periods. The precipitates are filtered, washed several times with distilled water and air-dried.
Sources
- Laurence C. Chow, Edward D. Eanes, "Octacalcium phosphate", Monograph in Oral Science, S. Karger AG, 2001, ISBN 978-3805572286.(Google books)
- Brown, W. E., Lehr, J. R.. Smith, J. P., Frazier, A. W., J. Am. Chem. Soc., 1957, 79 (19), 5318.
- M.J. Arellano-Jiméneza, M. J., García-Garcíaa, R., Reyes-Gasga, R. 2009. Journal of Physics and Chemistry of Solids 70, 390.
- LeGeros, R. Z., 1985. Calcif Tissue Int 37:194
- http://pubchem.ncbi.nlm.nih.gov Summary octacalcium phosphate. Last accessed 4/9/10
- www.pubmed.gov Octacalcium phosphate: Osteoconductivity and crystal chemistry. Suzaki, O. Last accessed 4/09/10
- Nelson, D.J.A., McLean, J.D., 1984. Calcif Tissue Int. 36, 219.
- Brown, W.E., Eidelman, N., Tomazic, B., 1987. Adv. Dent. Res., 1; 306
- http://www.ccmr.cornell.edu/facilities/Winners06Sum/dattran.html Cornell Center for Materials Research. Dat T. Tran. Last Accessed 4/09/10