Fluoride release from cements

Forsten, L. (1977). Fluoride release from a glass ionomer cement. Scandinavian Journal of Dental Research, 85, 503—4. 

Kuhn, A. T. Jones, M. P. (1982). A model for the dissolution and fluoride release from dental cements. Biomaterials, Medical Devices and Artificial Organs, 10, 281-93. 

Meryon, S. D. Smith, A. J. (1984). A comparison of fluoride release from three glass ionomer cements and a polycarboxylate cement. Interruitional... 

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]. 

As mentioned, fluoride release from set cements follows a distinctive pattern. First, there is a rapid burst of ion release that is non-linear with respect to time. This has sometimes been referred to as early wash-out , but actually is not confined to particularly early periods in a cement s life, as it has been shown to be discernible after 28 days [224]. 

R.W. Billington, P.C. Fladley, J.A. Williams, G.J. Pearson, Kinetics of fluoride release from zinc oxide-based cements. Biomaterials 22 (2000) 2507-2513. 

B.F. El Mallakh, N.K. Sarkar, Fluoride release from glass ionomer cements in deionized water and artificial saliva. Dent. Mater. 6 (1990) 118-122. 

S. Flatibovic-Kofman, G. Koch, Fluoride release from glass ionomer cement in vivo and in vitro, Swed. Dent. J. 5 (1991) 253-258. 

The ability of glass-ionomer cements to release fluoride is considered one of their important advantages [1], Huoride release can be sustained for very long periods of time, with up to 5 years having been demonstrated experimentally for specimens kept under running tap water [97], The pattern of fluoride release from a glass-ionomer is of an initial rapid release ( early burst ), followed by a sustained, lower level release that occurs by a diffusion mechanism [98-100]. These processes have been quantified and shown to follow the pattern described by the equation [101] ... 

A. Yoda, T. Nakaido, M. Ikeda, H. Sonada, R.M. Foxton, J. Tagami, Effect of curing method and storage condition on fluoride ion release from a fluoride-releasing resin cement. Dent. Mater. 25 (2006) 261-266. 

Figure 5.11 (Crisp Wilson, 1974b) shows the time-dependent variation of the concentration of soluble ions in setting and hardening cements. Note that the concentrations of aluminium, calcium and fluoride rise to maxima as they are released from the glass. After the maximum is reached the concentration of soluble ions decreases as they are precipitated. Note that this process is much more rapid for calcium than for aluminium and the sharp decline in soluble calcium corresponds to gelation. This indication is supported by information from infrared spectroscopy which showed that gelation (initial set) was caused by the precipitation of calcium polyacrylate. This finding was later confirmed by Nicholson et al. (1988b) who, using Fourier transform infrared spectroscopy (FTIR), found that calcium polyacrylate could be detected in the cement paste within one minute of mixing the cement. There was no evidence for the formation of any aluminium polyacrylate within nine minutes and substantial amounts are not formed for about one hour (Crisp et al, 1974).

Cranfield, M., Kuhn, A. T. Winter, G. (1982). Factors relating to the rate of fluoride-ion release from glass-ionomer cement. Journal of Dentistry, 10, 333-41. 

Although fluoride is added as the tin salt, fluoride release is accompanied by the release of aluminium and not tin (de Freitas, 1973). There is little leaching out of tin apart from an initial wash-out. Of course, aluminium is not released from the normal cement (Wilson, 1976 Wilson, Abel Lewis,... 

The dissolution and ion release from dental silicate cement have been the most investigated characteristics with good reason, for they are central to its clinical performance. Erosion limits its life but release of fluoride has important clinical consequences. 

Kuhn Jones (1982) examined various models for fluoride release and showed that release did not fit the membrane and homogenous monolith model. Instead, they concluded that the cement behaved as a porous granular monolith, as described by Kydonieus (1980). The release of fluoride appears to be an ion exchange phenomenon, as dental silicate cement takes up rather than releases fluoride from solution if it is present in sufficient concentration (Kuhn, Lesan Setchell, 1983). 

Aluminium ions released from the dental silicate cement are also absorbed by hydroxyapatite and have a similar beneficial effect to that of fluoride (Halse Hals, 1976 Putt Kleber, 1985). Thus, the dental silicate cement confers protection against caries (dental decay) on surrounding tooth material. 

Brauer, Stansbury Flowers (1986) modified these cements in several ways. The addition of various adds - acetic, propionic, benzoic etc. -accelerated the set. The use of zinc oxide powders coated with propionic add improved mixing, accelerated set, reduced brittleness and increased compressive strength from 63 to a maximum of 72 MPa. The addition of plasticizing agents such as zinc undecenylate yielded flexible materials. Incorporation of metal powders had a deleterious effect and greatly increased the brittleness of these cements. The addition of fluorides was not very successful, for fluoride release was not sustained. 

Glass-ionomer cements have been shown to be dynamic materials and, following the suggestion of Walls [238], to be capable of taking up fluoride from surrounding media. There have been several reports that fluoride release is enhanced following prior exposure to fluoride solution [239-243]. This effect has been demonstrated both in vitro and in vivo, and has been claimed to be evidence of fluoride uptake and re-release. 

P. Weidlich, L.M. Miranda, M. Maltz, S.M.W. Samuel, Fluoride release and uptake from glass ionomer cements and composite resins, Braz. Dent. J. 11 (2000) 89-96. 

M.G. Gandolfi, S. Chersoni, G.L. Acquaviva, G. Piana, C. Prati, R. Mongiorgi, Fluoride release and absorption at different pH from glass-ionomer cements. Dent. Mater. 22 (2006) 441 9. 

As with glass-ionomer cements, flnoride release from polyacid-modified composite resins is snstained for long periods of time [23] and is enhanced by placing the polyacid-modified composite resin in acidic storage media [25,36]. This property has been snggested to be beneficial in the case of resin-modified glass-ionomers [37], since it wonld lead to enhanced release of protective fluoride ion under the very conditions that promote dental caries. A similar argnment can be advanced for polyacid-modified composite resins, and it may be that this ability to release extra fluoride under conditions of low pH is beneficial clinically. 

In this section, three aspects of the interaction of resin-modified glass-ionomers with water are dealt with, namely water uptake, fluoride release and other ion release and its associated buffering effect. Like conventional glass-ionomer cements, resin-modified glass-ionomers are deployed in an essentially wet environment and their behaviour in terms of each of these features differs more or less from that of conventional glass-ionomers, due to the presence of the polyHEMA phase. These are considered in turn. 

N.K. Thanjal, R.W. BUhngton, S. Shahid, J. Luo, R.G. Hill, G.J. Pearson, Kinetics of fluoride ion release from dental restorative glass ionomer cements the influence of ultrasound, radiant heat and glass composition, J. Mater. Sei. Mater. Med. 21 (2010) 589-595. 

Similarly influence the soluble fluorides for example the F ions released from NaF to the solution form the insoluble CaFj which covers the cement grains. The complex fluorosilicates Na2SiFg and NajAlFg can additionally result in the precipitation of siUcate or aluminate gel on the surface of cement grain poor in calcium. Phosphogypsum, soluble calcium phosphates and sodium fluoroaluminates containing by-products exhibits the retarding effect too [96]. 

The glass polyalkenoate cement uniquely combines translucency with the ability to bond to untreated tooth material and bone. Indeed, the only other cement to possess translucency is the dental silicate cement, while the zinc polycarboxylate cement is the only other adhesive cement. It is also an agent for the sustained release of fluoride. For these reasons the glass polyalkenoate cement has many applications in dentistry as well as being a candidate bone cement. Its translucency makes it a favoured material both for the restoration of front teeth and to cement translucent porcelain teeth and veneers. Its adhesive quality reduces and sometimes eliminates the need for the use of the dental drill. The release of fluoride from this cement protects neighbouring tooth material from the ravages of dental decay. New clinical techniques have been devised to exploit the unique characteristics of the material (McLean Wilson, 1977a,b,c Wilson McLean, 1988 Mount, 1990). 

Wilson, A. D., Groffman, D. M. Kuhn, A. T. (1985). The release of fluoride and other chemical species from a glass-ionomer cement. Biomaterials, 6, 431-3. 

It is superior to the zinc phosphate cement for bonding orthodontic bands to teeth (Clark, Phillips Norman, 1977). It has greater durability and there is less decalcification in adjacent tooth enamel. This latter beneficial effect must arise from the release of fluoride which is absorbed by the enamel, so protecting it in a clinical situation where caries-produdng debris and plaque accumulate. 

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