Tooth fillings

Continuous phase zinc phosphates mostly crystalline minor amorphous 

Continuous phase calcium silicate hydrates mostly amorphous gel minor crystalline 

FIGURE 12.25 Comparison of cements (a) zinc phosphate dental cement and (b) Portland cement concrete. 

Immediately prior to use, phosphoric acid is mixed with an excess of zinc oxide. This sets within less than 5 min producing a core of ZnO particles anbedded in amatrix of crystalline and amorphous zinc phosphates. Subsequent hardening processes are associated with changes of crystallinity and the formation of more basic and insoluble salts (12.154). 

The setting rates of these dental cements are controlled by prior sintering of the oxide powder and by the addition of buffering aluminium salts to the phosphoric acid. Small quantities of MgO, Si02, AI2O3, and so on are usually included in the formulation. Anti-bacterial action can be achieved by the addition of some CuO which produces small quantities of non-white copper phosphates. 

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Biocorrosion of stainless steel is caused by exopolymer-producing bacteria. It can be shown that Fe is accumulated in the biofilm [2.62]. The effect of bacteria on the corrosion behavior of the Mo metal surface has also been investigated by XPS [2.63]. These last two investigations indicate a new field of research in which XPS can be employed successfully. XPS has also been used to study the corrosion of glasses [2.64], of polymer coatings on steel [2.65], of tooth-filling materials [2.66], and to investigate the role of surface hydroxyls of oxide films on metal [2.67] or other passive films. 

Wear of medical devices and biomaterials can affect quality of life. Wear of tooth fillings, artificial joints and heart valves can be inconvenient, costly (more frequent replacement) or even life-threateiiiiig (premature breakdowns). Wear of components can also cause accidents. Worn brakes and tires can cause automobile accidents, worn electrical cords can result in electrocution and fires and worn out seals can lead to radiation leaks at nuclear power plants. 

Dental silicate cement was once the most favoured of all anterior (front) tooth filling materials. Indeed, it was the only material available for the important task of aesthetic restoration from the early 1900s to the mid 1950s, when the not very successful simple acrylic resins made their appearance (Phillips, 1975). In the mid sixties there were some 40 brands available (Wilson, 1969) and Wilson et al. (1972) examined some 17 of these. Since that time the use of the cement has declined sharply. It is rarely used and today only two or three major brands are on the market. The reason for this dramatic decline after some 50 years of dominance is closely linked with the coming of modern aesthetic materials the composite resin from the mid 1960s onwards (Bowen, 1962), and the glass-ionomer cement (Wilson Kent, 1971) from the mid 1970s. 

While it feels as though all the mouth fills with this pain, in fact the pain only manifests itself through those teeth filled with metal, the metal being silver dissolved in mercury to form a solid - we call it a silver amalgam. Corrosion of the filling s surface causes it to bear a layer of oxidized silver, so the tooth filling also represents a redox couple, with silver and silver oxide coexisting. 

Worked Example 7.10 A tooth filling is made of a silver amalgam that comprises 37 mol% silver. What is the activity of the mercury, a(Hg) ... 

Eugenol may be mixed with zinc oxide as a temporary tooth filling, where the eugenol seeps into the pulp of the tooth and has anesthetic effects (Markowitz et al. 1992). 

The first literature reference was a patent issued in 1962 for a tooth-filling compound. Commercialization did not start until the late 1960s. 

This was assayed, rather remarkably, by attaching electrodes to the tooth fillings of the experimental subjects. But with this base, cardiovascular effects were not observed until doses of about 100 milligrams were administered, and toxic effects (nausea and vomiting) were reported at 150 milligrams. There was no suggestion of anything psychedelic. 

Lorscheider FL, Vimy MJ, Summers AO. Mercury exposure from silver tooth fillings emerging evidence questions a traditional dental paradigm. FASEB J 1995 9(7) 504-8. 

Mercury has been used for more fhan 150 years in dental silver amalgams. Dental silver amalgams in tooth fillings are composed of a mixture of 50% metalhc mercury and metal powder, usuaUy silver, tin, copper and zinc. 

Mercury and its compounds 7439-97-6 Batteries, thermometers, tooth filling, chlor-alkali industry... 

Halbach S. 1994. Amalgam tooth fillings and man s mercury burden. Human Exper Toxicol 13 496-501. 

Hahn LJ, Kloiber R, Vimy MJ, Takahashi Y, Lorschei-der EL. Dental silver tooth fillings A source of mercury exposure revealed by whole-body image scan and tissue analysis. FASEB J 1989 3 2641-6. 

Wantke F, Hemmer W, Haglmuller T, et al. 1995. Anaphylaxis after dental treatment with a formaldehyde-containing tooth-filling material. Allergy 50 274-276. 

Vimy, M.J., D.E. Hooper, W.W. King, and F.L. Lorscheider. 1997. Mercury fix n maternal silver tooth fillings in sheep and human breast milk. A source of neonatal exposure. Biol. Trace Elem. Res. 56(2) 143-152. 

Ahlqwist M, Bengtsson C, Furunes B, Hol-lendee L and Lapidus L (1988) Number of amalgam tooth fillings in relation to subjectively experienced symptoms in a study of Swedish women. Community Dent Oral Epidemiol 16 227-231. Ahmed R and Stoepplee M (1987) Storage and stability of mercury and methylmercury in sea water. Anal Chim Acta 192 109-113. 

Bisphenol-A (BPA) is used in the manufacture of epoxy resins and polycarbonate plastics. These compounds are then used in the manufacture of various other products, including tooth fillings, dental materials, and the coatings on the inside of food tins. BPA was identified as an estrogen mimic after tests with yeast conditioned media (see Figure 3). 

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