Fluoride cement reaction

Cement formation with fluoride glasses - - -)-tartaric acid The presence of (+)-tartaric acid in a cement formulation exerts a profound effect on the cement-forming reaction. The nature of the underlying chemical reaction is changed and this is reflected in time-dependent changes in viscosity. 

In neutral solution when fully hardened, dental silicate cements are resistant to aqueous attack. Before they have fully hardened, set cements contain soluble reaction intermediates - soluble sodium salts, acid phosphates and fluorides - which render them vulnerable to attack even by neutral solutions including saliva (Wilson, 1976). 

Fluorine is an essential element involved in several enzymatic reactions in various organs, it is present as a trace element in bone mineral, dentine and tooth enamel and is considered as one of the most efficient elements for the prophylaxis and treatment of dental caries. In addition to their direct effect on cell biology, fluoride ions can also modify the physico-chemical properties of materials (solubility, structure and microstructure, surface properties), resulting in indirect biological effects. The biological and physico-chemical roles of fluoride ions are the main reasons for their incorporation in biomaterials, with a pre-eminence for the biological role and often both in conjunction. This chapter focuses on fluoridated bioceramics and related materials, including cements. The specific role of fluorinated polymers and molecules will not be reviewed here. 

Not surprisingly, the use of acidified water increased the level of fluoride release from the glass, and this effectively models what happens in a setting cement. The acid-base reaction between the glass and the water-soluble polymeric acid liberates fluoride from the glass, causing it to move to the matrix, from where it is gradually leached as the cement releases fluoride [227,228]. 

Ions released into the matrix as the cement sets may interact with the organic part of the matrix. Metal ions, such as Ca + and AP+, may be chelated by car-boxylate groups, either on the polymer or on the tartaric acid additive. These have been considered in reasonable detail in the literature [230]. What has received far less attention is the possibility that fluoride ions might interact with carboxylic acid groups, either to modify the setting reaction or to become relatively securely anchored within the set cement. This possibility was raised in a review published in 1998 [230], but has not been followed up subsequently. It is based on the well-established observation that fluoride ion will form extremely strong hydrogen bonds with carboxylic acids in aqueous solution. They are of the type ... 

Hydrogen fluoride is produced worldwide in 10 ta by reaction of fluorspar with sulfuric acid (equation 1). The reaction is endothermic (AF/298 = 59kJmol ) and is carried out in rotary furnaces that produce up to 45td . The crude HF is scrubbed by H2SO4 and purified further by distillation as required. Silicon tetrafiuoride is a by-product from silicate impurities (equation 2) and is recovered as H2SiFe (equations). Another by-product, CaS04, is used in cement production and other applications. ... 

De Moor R, Verbeeck R, Martens L. [Evaluation of long-term release of fluoride by type II glass ionomer cements with a conventional hardening reaction]. Rev Beige Med Dent 1996 51(3) 22-35. 

ACID AMMONIUM FLUORIDE (1341-49-7) FiH H4N Reacts with water, forming a weak solution of hydrofluoric acid. Violent reaction with bases, releasing ammonia gas. Attacks glass, cement, and most metals in the presence of moisture. Upon contact with moisture and metal, this material may release flammable hydrogen gas which may collect in enclosed spaces. Do not use aluminum, nickel, or steel containers. When heated to decomposition, emits toxic and corrosive fumes of ammonia, hydrogen fluoride, and nitric oxides. 

In addition, they contain extra components. Part of the filler phase is made up of particles of fluoroaluminosilicate glass of the type used in glass-ionomer cements. There is also a small quantity of a proprietary acid-functional monomer, the so-called acid resin [ 1 ]. This is not sufficient to allow the monomer to be soluble in water, but it does confer a small degree of hydrophilic character on the set matrix. This causes water from the surroundings to be drawn into the structure, and results in ionization of the acid-functional groups and reaction with the ionomer glass component [38]. Any such reaction is limited, but potentially useful in allowing the set material to release fluoride. 

One of the properties of glass-ionomer cements that polyacid-modified composite resins are designed to possess is the ability to release fluoride. The reactive glass filler is an ionomer-type glass, and as such contains fluoride. This becomes available for release following its incorporation into the polysalt phase as a result of the moisture driven acid-base reaction with the acid-functional monomer component [1]. 

Since the days of the first commercial glass-ionomer cement there has been an enormous amount of research aimed at improving the properties to the extent that modem materials are superior in every aspect to the original ASPA material. An early critical discovery was the role of tartaric acid in moderating the setting reaction [17]. This allowed glasses of improved translucency and lower fluoride content to be developed. 

Glass-ionomer cements, which harden not by polymerization, but by the acid-base reaction between an aqueous polyelectrolyte (poly(acrylic acid) or related co-polymers) and a basic fluoro-aluminosilicate (FAS) glass. These materials are not as tough as resin composites, but they chemieally adhere to tooth tissue and are capable of releasing fluoride ions. 

Precaution Dust is flamm. attacked by dil. hydrochloric and sulfuric acids corrodes readily in air explosive reaction with ammonium nitrate + heat ignites on contact with bromine pentafluoride incandescent reaction with acetylene, nitryl fluoride Uses In alloys oxidizing agent lamp filaments in mfg. of cobalt steel, cobalt salts electroplating ceramics catalyst (sulfur removal from petrol., Oxo process, org. synthesis) trace element in fertilizers drier in inks, paints colors cermets in porcelain, glass, pottery, enamels pigment in paints food processing aid cemented carbides jet... 

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