Enamel acid solubility

Bitner, T. J. Weir, S. H. (1973). Fluoride uptake and acid solubility of enamel exposed to carboxylate cement containing MFP. Journal of Dental Research, 52, 157-62. 

Enamel Preparation. Soluble oligoester diols (Ib-ld, 2a-2g, and 3a-3g), HMMM, methyl isobutyl ketone (MIBK) and -toluenesulfonic acid ( -TSA) were thoroughly mixed in a 70/30/30/0.3 wt. ratio. The solution was cast on panels and baked at 150" for 30 min. Less soluble LC diols le-lg were melted, dispersed in MIBK, mixed with HMMM and -TSA in the above proportions and immediately cast as films. Oligoester diol la was too insoluble for enamel formation. 

Glimcher, M. J., Mechanic, G. L., Friberg, U. A. The amino acid composition of the organic matrix and the neutral soluble and acid soluble components of embryonic bovine enamel. Biochem. J. 93, 198 (1964)... 

Fluoride and Enamel. The presence or absence of fluoride in the apatite crystallites of enamel is said to be the most important of the environmental factors so far identified as influencing the caries-forming process (Morris and Greulich, 1968). In recent years research has focused on the still obscure mechanism by which the fluoride ion renders the crystalline structure of enamel less susceptible to attack. It has recently been established that the lattice perfection (crystallinity) of enamel improves with increase in fluoride content, and that it is this more perfect structure that renders the enamel less soluble in acid Also, the increased perfection achieved in enamel is not solely a function of lattice a-axis direction, as is the case in bone, but may be related more importantly to the c-axis. 

The mechanism by which fluoride ions inhibit caries is not fully understood [361]. One mechanism involves substitution reactions in the surface hydroxyapatite of enamel to create a concentration gradient of less acid-soluble, but iso-structural, fluoroapatite (fluoride content about 38 000 mg kg" ) ... 

Proteins are much less abundant in mature than in young enamel. Water-soluble material of low molecular weight, is probably distributed throughout the thickness of mature enamel, adsorbed on the hydroxyapatite. After demineralization, ribbons of an acid-insoluble protein, apparently of high molecular weight, are demonstrable mainly in the inner third of enamel fi om human molars. The insoluble protein probably represents mainly enamelins which have persisted in the mature enamel. The protein integument, acquired by the outer surface of the enamel after eruption, is clearly not a true enamel constituent. 

Saliva becomes more acidic when high-sugar foods are eaten. Brushing regularly with fluoride toothpaste helps prevent cavities by making tooth enamel less soluble in acid. 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

Organic acid Some glasses are more prone to attack by organic acids than by other acids with a lower pH value. These acids form complex ions in solution which increases the glass solubility. Many vitreous enamels contain lead oxide and are susceptible to attack by organic acids. Consequently their corrosion resistance is assessed by exposure to acetic or citric acidsThe test temperature is always stipulated because a rise of 10°C can double the rate of reaction between glass and acid. 

Following the same procedures described in the above-mentioned study, additional extractive data were obtained for the epoxy phenolic enamel that was irradiated at 4.7-7.1 Mrad at 25 and — 30 °C in the presence of distilled water, 3% acetic acid, and n-heptane. The changes in the amount of extractives resulting from the irradiation treatment are shown in Table IX. In the case of the water and acetic acid extractives, there was no change in either the chloroform-soluble fractions or the chloroform-insoluble fractions. In the case of the n-heptane extractives, the amount of extractives decreased when the irradiation temperature was reduced from +25 to — 30°C. Infrared spectra of the chloroform-soluble residues from the water and acetic acid extractives of the unirradiated and irradiated enamel were identical to the chloroform-soluble residues from the solvent blanks. In other words, the epoxy phenolic... 

In the following year Sir Everard Home interested Mr. Hatchett in the chemical composition of dental enamel (7, 8). Since the tooth of the elephant is composed of three different structures, Sir Everard wished to know whether the materials themselves were different or only differently arranged. Hatchett showed that the enamel was composed of calcium phosphate. The enamel, said he, has been supposed not a phosphate but a carbonate of lime. This error may have arisen from its solubility in acetous acid or distilled vinegar but the effects of the acetous acid are in every respect the same on powdered bone as on the enamel (8). 

An important example of the effect of pH on solubility is tooth decay. Tooth enamel contains the mineral hydroxyapatite, which is insoluble near neutral pH, but dissolves in acid because both phosphate and hydroxide in the hydroxyapatite react with H+ ... 

Fluorides. Sodium fluoride [CAS 7681-49-4], NaF. white solid, soluble, formed by reaction of sodium carbonate and hydrofluoric acid, and then evaporating. Used (1) as an antiseptic and antifermentative in alcohol distilleries. (2) as a food preservative, (3) as a poison for rats and roaches. (4) as a constituent of ceramic enamels and fluxes sodium hydrogen... 

The effect of pH on solubility is also important in understanding how fluoride ion reduces tooth decay. When tooth enamel comes in contact with F ions in drinking water or fluoride-containing toothpaste, OH- ions in hydroxyapatite, Ca5(PC>4)30H, are replaced by F- ions, giving the mineral fluorapatite, Ca5(PC>4)3F. Because F- is a much weaker base than OH-, Ca5(P04)3F is much more resistant than Cas(P04)30H to dissolving in acids. 

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