Hard tissues, calcium phosphate

Bone, or osseous tissue, is composed of osteocytes and osteoclasts embedded in a calcified matrix. Hard tissue consists of about 50% water and 50% solids. The solids are composed of cartilaginous material hardened with inorganic salts, such as calcium carbonate and phosphate of lime. 

Reconstituted acid-soluble collagen from various mineralized and unmineralized tissues have been examined for their potential to pick up calcium and phosphate from buffered solutions, and for their capacity to induce nucleation of a mineral phase426-434. Some collagens were good, others poor catalysts428,429 and apatite deposition proceeded in the presence of soft as well as of hard tissue collagens. The uptake of calcium ions requires the presence of phosphate ions and vice versa the Ca/P ratio is close to that of apatite (1.5—1.8)431. Study of exchange reactions by isotope tracers between solvent und substrate revealed that in absence of either... 

Matthews, J. L., Martin, J. H., Kennedy III, J. W., and Collins, E. J. An ultrastructural study of calcium and phosphate deposition and exchange in tissues. In Hard tissue growth, repair and remineralization (eds. K. Elliott and D. W. Fitzsimons), pp. 187-211. Amster-dam-London-New York Elsevier-Excerpta Medica-North-Holland 1973. 

Phosphates are found in soft organic tissues as phosphate esters, and in hard tissues, notably bones and teeth, as solid calcium orthophosphates see Biomineralization). Hard tissues are composites of Apatite and an organic matrix collagen in bone, dentin, and dental cement, and keratin in dental enamel. The Apatite phases are defective with Ca/P ratios of 1.6-1.8 and can incorporate other cations (Na+, K+, Mg +) or anions (F , d , COs ", citrate). 

Virtually all dentifrice formulations contain abrasive particles, typically composed of amorphous silica, calcium carbonate, alumina or calcium phosphate. The mechanism by which the toothbrush and dentifrice interact to clean the teeth is one of abrasive cleaning. Toothpaste manufacturers thus aim to provide formulations with effective cleaning power, whilst minimising any wear to the underlying substrate. However, in such a system it is inevitable that some degree of abrasivity will be present, as toothpastes without abrasive particles are unable to prevent the build-up of extrinsic stain [12], It is, therefore, important to understand any abrasion a dentifrice product may cause to the hard tissues in the mouth. 

Jarcho, M. (1981) Calcium phosphate ceramics as hard tissue prosthetics. Clin. Orthop. Relat. Res., 157, 259-278. 

Calcium phosphate A family of calcium phosphate ceramics including aluminum calcium phosphate, ferric calcium phosphate, hydroxyapatite and tricalcium phosphate (TCP), and zinc calcium phosphate which are used to substitute or augment bony structures and deliver drugs. Glass-ceramics A glass crystallized by heat treatment. Some of those have the ability to form chemical bonds with hard and soft tissues. Bioglass and Ceravital are well known examples. 

Bajpai P.K. 1990. Ceramic amino acid composites for repairing traumatized hard tissues. In Handbook of Bioactive Ceramics, Vol. II Calcium Phosphate and Hydroxylapatite Ceramics. T. Yamamuro, L.L. Hench, and J. Wilson-Hench (Eds.), pp. 255-270. CRC Press, Baton Raton, FL. 

The hard tissue of the tooth substance consists of a protective outer coat of enamel and an underl nng dentin phase. The latter, in turn, connects to the inner core of soft tissue pulp), which is interpenetrated by nerve strands and blood vessels. The enamel, which covers essentially the visible part of the tooth and indeed represents the hardest tissue in the body, is composed almost entirely (97% by weight) of mineral-type hydroxyapatite (a crystalline calcium phosphate) in addition to a few percent of water and organic, mostly proteinaceous, matter. Dentin, constituting the major proportion of tooth substance, contains less mineralized phase (69% hydroxyapatite) but a comparatively large proportion of organic matter and water. Compositional and physical property data for enamel and dentin [3] are summarized in Tables 1 and 2. 

General metabolic significance. Vitamin D stimulates intestinal absorption of calcium and phosphate, renal reabsorption of these ions, deposition and mobilization of minerals in the hard tissue, controlling normal calcium and phosphate blood level by means of these processes. Molecular mechanism of the vitamin D effects most frequently conform to the effect of steroid hormones (induction of protein biosynthesis). 

Hydroxyapatite, Caio(P04)6(OH)2, is the main inorganic component found in hard human tissues such as bone and teeth and is the most extensively used bioceramic in bone tissue engineering. The other materials used for this purpose include alumina, zirconia, titania phosphates, and calcium phosphates [such as calcium tetraphosphate (Ca4P209) and tricalcium phosphate Ca3(P04)2] and derivatives [47, 48]. The chemical stmcture of HAp is presented in Fig. 5 [49]. 

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