Teeth, composition

Unfilled Tooth Restorative Resins. UnfiUed reskis were some of the first polymer materials iatroduced to repak defects ki anterior teeth where aesthetics were of concern. They have been completely replaced by the fiUed composite reskis that have overcome the problems of poor color StabUity, low physical strength, high volume shrinkage, high thermal expansion, and low abrasion resistance commonly associated with unfiUed reskis. 

Alloys are metallic materials prepared by mixing two or more molten metals. They are used for many purposes, such as construction, and are central to the transportation and electronics industries. Some common alloys are listed in Table 5.5. In homogeneous alloys, atoms of the different elements are distributed uniformly. Examples include brass, bronze, and the coinage alloys. Heterogeneous alloys, such as tin-lead solder and the mercury amalgam sometimes used to fill teeth, consist of a mixture of crystalline phases with different compositions. 

The properties of alloys are affected by their composition and structure. Not only is the crystalline structure important, but the size and texture of the individual grains also contribute to the properties of an alloy. Some metal alloys are one-phase homogeneous solutions. Examples are brass, bronze, and the gold coinage alloys. Other alloys are heterogeneous mixtures of different crystalline phases, such as tin-lead solder and the mercury-silver amalgams used to fill teeth. 

Nanostructured materials are nothing new. Chrysotile fibers are an example (Fig. 16.22), as are bones, teeth and shells. The latter are composite materials made up of proteins and embedded hard, nanocrystalline, inorganic substances like apatite. Just as with the imitated artificial composite materials, the mechanical strength is accomplished by the combination of the components. 

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... 

Teeth, the hard conical structures embedded in their jaws that vertebrate animals use to chew food, consist of two layers of compact matter surrounding a core of soft, living tissue. The inner layer is composed of dentine, also known as ivory, whose composition is similar, but not identical, to that of bone it contains less collagen and is harder than bone. The thin outer layer of the teeth, the teeth s enamel, includes even less collagen and other organic matter than dentine and is the hardest substance produced by animals (Hilson 1986a Kurten 1986b 1982). 

Strontium incorporated into the teeth, for example, becomes immobilized after formation of the teeth. The relative amounts of the isotopes of strontium in the teeth is, therefore, related to the average strontium isotope composition that an animal ingested in food or water while growing. Thus teeth retain a kind of record of both early exposure to the isotopes of strontium in the water and food ingested during their growing, early life. In the... 

Goldberg, M., J.P. Carreau, F.C.M. Driessens, and D. Septier. 1990. Zinc deficiency-induced changes in the lipid composition and ultrastructure of rat incisor teeth. Arch. Oral Biol. 35 255-264. 

Levinson, A.A., Luz, B. and Kolodny, Y. (1987). Variations in oxygen isotope compositions of human teeth and urinary stones. Applied Geochemistry 2 367-371. 

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