Teeth

May Mellanby, in very careful work well reviewed by Mellanby and King (1039), studied the structural relations of the teeth in children and in experimental work in dogs. The development of enamel hypoplasia as a result of vitamin D deficiency was established. The formation of secondary dentine as a function of the supply of fat-soluble vitamins was also recorded. 

The problem of dental decay is certainly a formidable one and can only be mentioned in passing here. Local factors may be of primary importance, but the role of the resistance of the tooth should not be minimized. May Mellanby saw some decrease in the incidence of caries 

Lately, May Mellanby and H. Mellanby (1948) have studied anew the correlation between enamel hypoplasia and caries, and the statistics leave little doubt that the hypoplastic tooth, irrespective of the locality in the mouth, can decay more readily and with greater frequency than the corresponding tooth with perfectly smooth surfaces. On other dietaries the correlation may not be significant, as indicated by Marshall-Day s (1944) report of studies in Indian children with well-developed hypoplasia and little caries. 

the hard conical structures embedded in their jaws that vertebrate animals use to chew food, consist of two layers of compact matter sur-roxmding 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). 

or dentine, the main constituent of the teeth of mammals, is a relatively hard, cream-white material that can be carved or mechanically formed, and its surface can be polished to a high shine (O Connor et al. 1987 Wills 1968). Of particular interest is the ivory that makes up the tusks (large incisor teeth) of large mammals such as elephants, hippopotami, whales, narwhals, and 

A tooth consists of three basic parts, the crown, which is exposed, the neck, which is at the gum line, and the root, which is embedded in the gum andjaw. The crown may be completely or partially covered with a harder substance known as enamel. The bulk of the tooth is composed of dentine, which surrounds and protects the inner pulp cavity. Pulp is vascular tissue that contains nerves and blood vessels, fed from below through a narrow channel in the dentine called the root canal. The root of the tooth is also surrounded by 

A Sioux craftsman fashioned this quirt from an elk antler. It had thongs of hide strung through the holes on the tines. 

Dentine is composed of a mixture of about 70% hydroxlyapatite (Ca5(P04)3(0H)), 20% collagenous proteins and about 10% water. The microscopic structure of dentine consists of microscopic canals called dentinal tubules that radiate out from the pulp cavity to the cementum border. The diameter of these canals varies among different animals, and ranges 

The handles of these tools are made from antler. The characteristic ridges are clear, and have been smoothed by 

Tooth enamel is the hardest tissue in an animal s body. It is composed almost entirely of inorganic hydroxyapatite, with less than 5% organic components and water. Most tooth enamel is from 1.5 to 2.0 mm thick, and may vary in thickness between teeth and even on a single tooth. 

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M.p. 190-192 C. The enolic form of 3-oxo-L-gulofuranolactone. It can be prepared by synthesis from glucose, or extracted from plant sources such as rose hips, blackcurrants or citrus fruits. Easily oxidized. It is essential for the formation of collagen and intercellular material, bone and teeth, and for the healing of wounds. It is used in the treatment of scurvy. Man is one of the few mammals unable to manufacture ascorbic acid in his liver. Used as a photographic developing agent in alkaline solution. 

Vitamin Dj has m.p. 115-117°C and D, m.p. 82 83 "C. Both vitamins, which have almost identical actions, are used for the prevention and cure of infantile rickets they are essential for the normal development of teeth, and are used for treating osteomalacia and dental caries. They are necessary for the absorption of Ca and P from the gut. 

Plenary 79. FI G M Edwards, e-mail address h.g.m.edwards bradford.ac.uk (NIR-FTRS). A review of recent applications of RS to archeology—characterizing ancient pigments, human skin, bone, ivories, teeth, resins, waxes and gums. Aging effects and dating possibilities. Emphasizes use of microscopic Raman. 

Phosphorus, like nitrogen, is an essential constituent of living matter where it may be partly in combination (as phosphate groups) with organic groups, for example in lecithin and egg yolk, or mainly in inorganic form, as calcium phosphate(V), in bones and teeth. 

Fluorine occurs widely in nature as insoluble fluorides. Calcium fluoride occurs as jluospar or fluorite, for example in Derbyshire where it is coloured blue and called bluejohn . Other important minerals are cryolite NajAlFg (p. 141) and Jluorapatite CaFjSCaj (P04)2. Bones and teeth contain fluorides and some natural water contains traces. 

The presence of fluorine as a soluble fluoride in drinking water to the extent of 2 ppm may cause mottled enamel in teeth, when used by children acquiring permanent teeth in smaller amounts, however, fluorides are added to water supplies to prevent dental cavities. 

Calcium is a metallic element, fifth in abundance in the earth s crust, of which if forms more than 3%. It is an essential constituent of leaves, bones, teeth, and shells. Never found in nature uncombined, it occurs abundantly as limestone, gypsum, and fluorite. Apatite is the fluorophosphate or chlorophosphate of calcium. 

Falling rod viscometer Fallopian tubes False teeth Falvin... 

Dry Foods. Dry foods are concentrated sources of nutrition and provide the most economical nutritional value because water in canned foods is expensive. Dry foods tend to scrape the teeth as pets eat, minimizing tartar deposition. When dry food is moistened prior to being consumed, tartar accumulates in a manner comparable to deposits observed with caimed foods. Approximately 95 to 98% of dry-type cat and dog foods are made by the extmsion process the remainder is made by pelleting or baking. 

Fluoridation of potable water suppHes for the prevention of dental caries is one of the principal uses for sodium fluoride (see Water, municipal WATER treatment). Use rate for this appHcation is on the order of 0.7 to 1.0 mg/L of water as fluoride or 1.5 to 2.2 mg/L as NaF (2). NaF is also appHed topically to teeth as a 2% solution (see Dentifrices). Other uses are as a flux for deoxidiziag (degassiag) rimmed steel (qv), and ia the resmelting of aluminum. NaF is also used ia the manufacture of vitreous enamels, ia pickling stainless steel, ia wood preservation compounds, caseia glues, ia the manufacture of coated papers, ia heat-treating salts, and as a component of laundry sours. 

Although the Rockwell test is intended to be used on flat parallel-sided specimens, its use can be extended to rounded surfaces by using a curvature correction factor. Compound surfaces such as gear teeth can be tested but the results must be corrected for curvature. 

Mu/tihearth Furnace. Multihearth furnaces are most often used for incineration of municipal and industrial sludges, and for generation and reactivation of char. The main components of the multihearth are a refractory-lined shell, a central rotating shaft, a series of soHd flat hearths, a series of rabble arms having teeth for each hearth, an afterburner (possibly above the top hearth), an exhaust blower, fuel burners, an ash removal system, and a feed system. 

The feed is normally introduced to the top hearth where the rabble arms and teeth attached to the central shaft rotate and spiral soflds across the hearth to the center, where an opening is provided and the soflds drop to the next hearth. The teeth of the rabble arms on the hearth spiral the soflds toward the outside to ports that let the soflds drop down to the next hearth. Soflds continue downward, traversing each hearth until they reach the bottom and the ash is discharged. The primary advantage of this system is the long residence time in the furnace controlled by the speed of the central shaft and pitch of the teeth. 

Elastohydrodynamic Lubrication (EHL). Lubrication needs in many machines ate minimized by carrying the load on concentrated contacts in ball and toUet beatings, gear teeth, cams, and some friction drives. With the load concentrated on a small elastically deformed area, these EHL contacts ate commonly characterized by a very thin separating hydrodynamic oil film which supports local stresses that tax the fatigue strength of the strongest steels. 

Dental x-rays provide valuable information on the health of teeth which cannot be obtained by any other medical imaging modaUty. Dental x-ray procedures use a piece of film placed in the mouth between the tongue and the teeth. A 60 to 70 keV source of x-rays, located outside the mouth, is directed at the film. Metal fillings attenuate x-rays striking the film and therefore appear white in a projection image. Tooth decay appears dark as it attenuates x-rays less than normal tooth enamel. 

Dentistry. Mercury is used in dental amalgams for fillings in teeth (see Dental materials). Dental uses have accounted for 2—4% of total U.S. mercury consumption since 1980 and generally 3—6% before that time (3). Dental amalgams used to fill cavities in teeth are approximately 50% mercury by weight. Dental use of mercury can be expected to continue to decrease, in part because of more effective cavity prevention as well as development and increasing use of alternative dental materials such as plastics and ceramics, and increasing awareness of the environmental and health effects of mercury. 

Medicine. The polymethacrylates have been used for many years in the manufacture of dentures, teeth, denture bases, and filling materials (116,117) (see Dental materials). In the orthodontics market, methacrylates have found acceptance as sealants, or pit and fissure resin sealants which are painted over teeth and act as a barrier to tooth decay. The dimensional behavior of curing bone-cement masses has been reported (118), as has the characterization of the microstmcture of a cold-cured acryUc resin (119). Polymethacrylates are used to prepare both soft and hard contact lenses (120,121). Hydrogels based on 2-hydroxyethyl methacrylate are used in soft contact lenses and other biomedical appHcations (122,123) (see Contactlenses). 

Phosphorus. Eighty-five percent of the phosphoms, the second most abundant element in the human body, is located in bones and teeth (24,35). Whereas there is constant exchange of calcium and phosphoms between bones and blood, there is very Httle turnover in teeth (25). The Ca P ratio in bones is constant at about 2 1. Every tissue and cell contains phosphoms, generally as a salt or ester of mono-, di-, or tribasic phosphoric acid, as phosphoHpids, or as phosphorylated sugars (24). Phosphoms is involved in a large number and wide variety of metaboHc functions. Examples are carbohydrate metaboHsm (36,37), adenosine triphosphate (ATP) from fatty acid metaboHsm (38), and oxidative phosphorylation (36,39). Common food sources rich in phosphoms are Hsted in Table 5 (see also Phosphorus compounds). 

Fluorine. Fluoride is present in the bones and teeth in very small quantities. Human ingestion is from 0.7—3.4 mg/d from food and water. Evidence for the essentiaUty of fluorine was obtained by maintaining rats on a duoride-free diet, resulting in decreased growth rate, decreased fertihty, and anemia. These impairments were remedied by supplementing the diets with duoride (81). Similar effects have been reported in goats (82). 

Niobium carbide is used as a component of hard metals, eg, mixtures of metal carbides that are cemented with cobalt, iron, and nickel. Along with tantalum carbide, niobium carbide is added to impart toughness and shock and erosion resistance. The spiraling rise in the price of tantalum has spurred the development of a hafnium carbide—niobium carbide substitute for tantalum carbide (68). These cemented carbides are used for tool bits, drill bits, shovel teeth, and other wear-resistant components turbine blades and as dies in high pressure apparatus (see Carbides). 

As fibers in the feed mat pass between the feed toU and feed plate, they ate separated by metallic wine teeth on the lickerin toU and carried to an air venturi where they ate stripped and tumbled until they strike a moving, perforated collection surface. At the collection surface, the airborne fibers foUow paths of least resistance and accumulate in a self-leveling manner while the air passes through perforations. Fiber orientation in the web is isotropic in layers corresponding to the number of fibers transferred from the wine teeth to the air-transportation 2one, the intensity of the air, and the speed of the collection surface. 

Nuts have many uses, both industrial and domestic. For instance, the ivory nut, or tagua, is a source material for the manufacture of buttons and turnery articles. The kola nut supplies ingredients for popular cola beverages in the United States (see Carbonated beverages). StTychnos nux-vomica provides the important medicine and poison, strychnine. The areca or betel nut is chewed by the Indian and Malayan people as a narcotic a slice of the nut is placed in a leaf of the pepper plant Piper betle) together with a pinch of lime the mixture is an acrid, astringent narcotic that dyes the mouth red, blackens and destroys the teeth. The areca nut contains, among other alkaloids, arecoline, an active anthelminthic widely used in veterinary practice for the treatment of tapeworm infections. 

Calcium Phosphates. The alkaline-earth phosphates are generally much less soluble than those of the alkaH metals. Calcium phosphates include the most abundant natural form of phosphoms, ie, apatites, Ca2Q(P0 3X2, where X = OH, F, Cl, etc. Apatite ores are the predominant basic raw material for the production of phosphoms and its derivatives. Calcium phosphates are the main component of bones and teeth. After sodium phosphates, the calcium salts are the next largest volume technical- and food-grade phosphates. Many commercial appHcations of the calcium phosphates depend on thek low solubiHties. 

In dentistry, palladium alloys are widely used as alternatives to base metal alloys in the manufacture of crowns and bridges as weU as the replacement of lost or damaged teeth (see Dental materials). Such alloys contain over 80% palladium, and hence offer significant cost benefits over alloys containing a high proportion of gold. 

Fig. 4. Typical design elements foi wet deagglomeiation in low viscosity systems (a) a high, ipm lotoi (shown below its normal position within stator) produces turbulence and cavitation as blades pass each other (b) a rotating disk creates a deep vortex to rapidly refresh the surface, and up- and downtumed teeth at the edge cause impact, turbulence, and sometimes cavitation and (c) the clearance of a high rpm rotor can be reduced as the batch...

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