Enamel dental applications

The following chapters are devoted to applications of phosphorus-based materials. Thus Chapter 8 by Mozsner and Catel deals with the use of polymerizable phosphonic acids (PAs) and dihydrogen phosphates (DHPs) for dental applications. Several PAs and DHPs were synthesized to notably improve the shear bond strength to dentin and enamel, the stability of the adhesive formulation, and the chemical adhesion to tooth tissues. Some of these monomers are nowadays included in commercial dental adhesives. 

Calcium fluoride (Fp. 1423 °C solubility in water 0,02 g/1 at 20 °C) is employed in aluminium metallurgy, brake lining, glass manufacturing, enamel [63] and glazing frits production, dental applications and in the production of welding agents. 

Figure 5.20 The effect of a citric acid solution on tooth structure (a) enamel surface before application, (b) enamel surface after application showing etching, (c) dentine surface before application, (d) dentine surface after application showing the opening-up of the dental tubules (Powis et al, 1982).

Crosslinked polymers are widely used as dental materials (1-31. Perhaps the most challenging application is in the restoration of teeth (4). The monomers must be non-toxic and capable of rapid polymerization in the presence of oxygen and water. The products should have properties comparable to tooth enamel and dentin and a service life of more than a few years. In current restorative materials such properties are sought using so-called "dental composites" which contain high volume fractions of particulate Inorganic fillers (5-71. However in the present article attention is concentrated on one commonly used crosslinked polymeric component, and on the way in which some of its properties are influenced by low volume fractions of fillers. 

Zinc oxide occurs in nature as mineral zincite. It is the most important zinc compound and has numerous industrial applications. Zinc oxide is the pigment in white paints. It is used to make enamels, white printing inks, white glue, opaque glasses, rubber products and floor tiles. It is used in cosmetics, soaps, pharmaceuticals, dental cements, storage batteries, electrical equipment, and piezoelectric devices. Other applications are as a flame retardant, as a UV absorber in plastics, and a reagent in analytical chemistry. A major application of zinc oxide is in the preparation of most zinc salts. In medicine, the compound is used as an antiseptic, an astringent and a topical protectant. 

The use of high-concentration gels and varnishes has been practised clinically for many years by dentists and dental hygienists [180]. When originally formulated, they were designed to be used in application procedures based on the concept that fluoride becomes incorporated into the crystalline phase of the enamel and leads to the development of a more acid-resistant form of apatite. They were not expected to make any difference to the levels of fluoride in saliva, or to influence the demineralisation/dissolution phase of the behaviour of tooth mineral. 

Fluoride in drinking water appears to be most effective in preventing dental caries if consumed before the eruption of the permanent teeth. The optimum concentration in drinking water supplies is 0.5-1 ppm. Topical application is most effective if done just as the teeth erupt. There is little further benefit to giving fluoride after the permanent teeth are fully formed. Excess fluoride in drinking water leads to mottling of the enamel proportionate to the concentration above 1 ppm. 

Grobler SR, Ogaard B, Rolla G Uptake and retention of fluoride in sound dental enamel in vivo after a single application of neutral 2% sodium fluoride, in Rolla G, Sonju T, Embery G (eds) Tooth Surface Interactions and Preventive Dentistry. London, IRL Press Ltd, 1981, pp 17-25. 

The Biomineralization section begins with a summary of the current state of research on bone, dentin and enamel phosphates, a topic that crosses disciplines that include mineralogical, medical, and dental research. The following two chapters treat the stable isotope and trace element compositions of modern and fossil biogenic phosphates, with applications to paleontology, paleoclimatology, and paleoecology. 

Another application of dental composites is orthodontic archwires. One example is a unidirectional pultruded S2-glass-reinforced dimethacrylate thermoset resin. Depending on the yam of glass fiber used, the fiber volume fraction varied from 32 to 74 percent The strength and modulus were comparable with those of titanium wires. Orthodontic brackets were also made from composites with a polyethylene matrix reinforced with ceramic hydroxyapatite particles, resulting in isotropic properties and good adhesion to enamel. 

Acidic monomers could be phosphates as well as carboxylic, sulfonic, or phosphonic acids. Some examples of carboxylic acid monomethactylates are 4-(2-methactyloyloxyethyl)trimellitic acid (4-MET) and 11-methactyloyloxy-1,1-undecanedicarboxylic acid (MAC-10). Among the functionalized monomers, free-radically polymerizable phosphonic acids (PAs) and dihydrogen phosphates (DHPs) have found wide and intensive applications as adhesive components in enamel/dentin adhesives. In this chapter, a review of the various PAs and DHPs prepared for application in dental adhesives is provided. 

The initial results demonstrate that molecular prototype delivery systems are able to harness free radical reactivity within the laboratory. Proof of the concept has also highlighted the importance, as well as plausibility, of innovative development of functional dental restorative materials that have bioactive and bonding properties suitable for use in dentin and enamel that also show beneficial preventative and therapeutic properties [215,216]. Further evaluation is required in the application of these novel drug-delivery systems for the prevention and treatment of disease states mediated by free radicals. 

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