Bone and Teeth Structure

A variation of calcium phosphate is the major component of bones and teeth in all vertebrates including humans. These calcium phosphates are usually referred to collectively as biological apatites, which are nonstoichiometric compounds based on pure apatites, Ca5(P04)3X, where X can be fluorine (F), chlorine (Cl), or hydroxyl (OH). (These are called fluoro-, chloro-, and hydroxyapatite, respectively.) In biological apatites the calcium cations can be replaced with varying amounts of strontium, magnesium, sodium, and potassium ions, and the phosphate anions can be replaced with hydrogen phosphates and carbonates. 

Human bones contain 60-70% (by mass) calcium phosphate. They provide mechanical support but also store the calcium and phosphate ions that are used in the body for a variety of functions. Bones are not permanent structures but instead exist in a state of dynamic equilibrium with their surrounding tissues. Biological apatite is continually dissolving and recrystallizing in the body. This equilibrium state makes it possible to maintain the necessary concentrations of calcium and phosphate ions in body fluids such as blood and saUva. 

Human teeth are also composed primarily of biological apatite. The outer two layers of a human tooth consist of enamel on the outside and dentine underneath that. Dentine and bones are very similar in composition and mechanical properties, but enamel is almost pure hydroxyapatite, Ca5(P04)30H. Dental enamel is the hardest part of the human body. In addition, the hardness of dental enamel is enhanced by the presence of fluoride ions in place of the hydroxides. (Thus we see 

Just as calcium carbonate was one of the cornerstones (pun intended) of the Roman economy, so it remains today. Limestone and marble remain popular for building materials, although they are degraded to the more soluble gypsum by acid rain, as represented in Equation (13.19)  

Stone leprosy at Herten Castle near Recklinghausen, Westphalia, Germany. The 

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As shown in Section 2.4.6, natural hydroxy/carbonate apatite in human bones and teeth structures exhibits a needleshaped habit. It has been a longstanding objective in the development of biomaterials to reproduce these... 

Topics under the practical importance of the alkaline-earth metals include their significance in living systems, the incidence of beryllium disease, radiochemical applications as components and residues of nuclear power, metallurgical uses in preparing pure metals and alloys, use in fireworks and X-ray technology, the definition and properties of hard water, and the role of calcium phosphate in bone and teeth structure. 

Phosphate fertilizers have been known for more than 150 years. Phosphate rock contains minerals such as calcium fluorapatite, Ca5(P04)3F, which are generally too insoluble to be of much use for plant uptake. (See pp. 367 and 554 for several viewpoints on the role of the insoluble calcium apatites in bone and teeth structure.)... 

Collagen is the most abundant animal protein in the body of animals, where it makes up as much as one-quarter of all the proteins. It is a fibrous protein that provides structure to and protects and supports soft tissues it also connects tissues to the skeleton. Collagen forms, for example, most of the resilient layers that make up the skin and the filaments that support the internal organs. Interwoven with bioinorganic components, collagen also makes up the bones and teeth of vertebrate animals (see Chapter 15). 

The bones and teeth of humans and other vertebrate animals, for example, consist mainly of a composite material made up of an organic substance, collagen, and a biomineral, calcium carbonate phosphate (see Textboxes 32 and 61). The latter, which makes up about two-thirds of the total dry weight of bone, is composed of calcium phosphate containing between 4-6% calcite (composed of calcium carbonate) as well as small amounts of sodium, magnesium, fluorine, and other trace elements. The formula Ca HPChXPChMCChXOH) approximately represents its composition its crystal structure is akin to that... 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Ca5(P04)30H]2, usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralization process leading to the hardest mineralized tissue known, the enamel of mammalian teeth. 

The calcium ion is a key factor in human nutrition. It has an important structural role in bone and teeth and is a regulatory factor in many aspects of metabolism. 

Structural — collagen production for vessel walls, skin, bones, and teeth ... 

While CaC03 crystals (calcite and aragonite) predominantly appear in egg shells and in biomineralisates from invertebrates, calcium phosphates are predominantly involved in processes which play an inportant role in medicine. They will be described here in detail the knowledge of their structures are most relevant for the understanding of the cellular and molecular processes in bones and teeth. 

Collagen is the major protein of the extracellular connective tissues and functions as a structural protein for many biomineralization processes, e. g. in bone and teeth. 

The insoluble Ca(II) salts of weak acids, such as calcium phosphate, carbonate, and oxalate, serve as the hard structural material in bone, dentine, enamel, shells, etc. About 99% of the calcium found in the human body appears in mineral form in the bones and teeth. Calcium accounts for approximately 2% of body weight (18,19). The mineral in bones and teeth is mosdy hydroxyapatite [1306-06-5] having unit cell composition Ca10(PO4)6(OH)2. The mineralization process in bone follows prior protein matrix formation. A calcium pumping mechanism raises the concentrations of Ca(II) and phosphate within bone cells to the level of supersaturation. Granules of amorphous calcium phosphate precipitate and are released to the outside of the bone cell. There the amorphous calcium phosphate, which may make up as much as 30—40% of the mineral in adult bone, is recrystallized to crystallites of hydroxyapatite preferentially at bone collagen sites. These small crystallites do not exceed 10 nm in diameter (20). 

COLLAGEN. The major protein component of connective tissue. In mammals, as much as 60% of ihc total body protein is collagen. It comprises most of the organic matter of skin, tendons, bones, and teeth, and occurs as fihrous inclusions in most other body structures. Collagen libers are easily identified on the basis of the following characteristic properties ... 

The calcium taken up by living systems will be found mainly as extracellular deposits or structures, with a small amount present in intracellular stores, together with some in various extracellular fluids. The calcium in fluids will be bound to protein or will be free in solution, with a few percent bound to small molecules or anions. The calcium in solution will exchange with the calcium in structures such as bone and teeth, due to the activity of hormones such as l,25-(OH)2D3, parathyroid hormone and calcitonin,455 which are responsible for the remodelling and repair of bone. 

The level of calcium in solution will depend upon the presence of precipitating anions, notably phosphate and carbonate. Calcium will precipitate as the phosphate to give hydroxyapatite, Caio(P04)6(OH)2, in bones and teeth, and as the phosphate or carbonate to give other structures, including small crystals, or non-crystalline deposits in cells. Small crystals of calcium carbonate, found in the inner ear of some animals, are responsible for the control of balance. Various calcified tissues result from the precipitation of calcium salts, such as hydroxyapatite in the calcification of the aortic wall, and the oxalate in various stones. 

Up to this point, we have summarized the NMR parameters of some selected crystalline compounds. Model crystalline compounds of calcium phosphates are important structural reference for the study of biominerals because the highly complex hierarchical structures of bones and teeth contain different phosphorus species such as unprotonated orthophosphate (PC>43 ) and protonated orthophosphate (HP042 ).70,77 It is beyond doubt that 31P chemical shifts are the most important spectroscopic parameters for the characterization of calcium phosphates. While the 31P chemical shift can reflect the protonation state of a phosphate species, 31P CSA is a sensitive measure of the symmetry of the electronic... 

Collagen is a major structural element in connective tissues skin, tendons, muscle, and internal organs. It combines with inorganic compounds in bones and teeth. Cartilage is collagen mixed in an amorphous gel. Dentine, which makes up the bulk of a tooth, is a mixture of collagen and hydroxyapatite (a mineral), and water. 

In contrast with the functional enzymes, there are purely structural proteins such as collagen. Collagen is the tough protein of tendons and is present in skin, bone, and teeth. It contains large amounts of glycine (every third amino acid is glycine), proline, and hydroxyproline (again about a third of the amino acids are either Pro or Hyp). 

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