Loss Of Fluoride Research Articles

Acid resistance of enamel exposed to fluoride-containing orthodontic cements

In a previous study enamel fluoride uptake from fluoride-containing orthodontic cements was evaluated after a 21-day period. The enamel fluoride uptake from a zinc phosphate cement (A), a zinc phosphate cement containing 5 per cent stannous fluoride by weight (B), and a silicophosphate cement (C) was compared. The results indicated that there was a net loss of fluoride from enamel beneath the orthodontic bands cemented with A while the enamel beneath B and C acquired significant amounts of fluoride. The purpose of the present study was to evaluate enamel fluoride uptake after 12 weeks and the effect of the fluoride uptake or loss by the enamel on acid resistance. Five teeth each had bands cemented with cements A, B, and C, respectively, and were individually suspended in synthetic saliva for 12 weeks at 37 ° C. Following this period the bands were removed, the cements were carefully cleaned off the teeth, and the crowns of the teeth were individually suspended in a lactic acid buffer at pH 4 for 4 weeks. Each tooth crown was then sectioned longitudinally and examined microradiographically to study the degree of enamel demineralization. Characteristic subsurface enamel carieslike lesions were noted on all the specimens studied. The carieslike lesions in the enamel exposed to the fluoride-containing cements were considerably reduced. The enamel which had acquired fluoride from the fluoride-containing cements was apparently more resistant to artificial caries attack.

Mechanism of fluoride loss from fluoropolytungstates possessing the keggin structure

The fluoropolytungstates [H 2W 12F 2O 38] 4− and [HW 12F 3O 37] 4−, which are of the metatungstate type with the fluoride ions occupying inner sites, lose fluoride ion and form more higly charged species [H 2W 12FO 39] 5− and [HW 12F 2O 38] 5− in aqueous solution about pH 3 in media of suitable ionic strength. Kinetic results are presented here consistent with a mechanism involving less condensed species containing 11 tungsten and 1, 2 or 3 fluoride atoms. Involvement of such species is supported by the isolation of the aluminotungstates [HW 11AlF 3O 36(H 2O)] (TMA) 5 †, 30H 2O and [H 2W 11AlF 2O 37(H 2O)](TMA) 5, 17H 2O.

Perfluoroisopropylidene and perfluoroisopropenyl derivatives of phosphorus. 1. Synthesis of perfluoroisopropenylphosphonates

1. Esters of pentafluoroisopropenylphosphonic acid were obtained by dehydrofluorination of the corresponding esters ofα-hydrohexafluoroisopropylphosphonic acid or the loss of alkyl fluoride from hexafluoroisopropylidenetrialkoxyphosphoranes by the action of the adduct Et3N·BF3. 2. The action of catalytic amounts of Et2O·BF3 on hexafluoroisopropylidenetrimethoxyphos-phorane leads to its rearrangement to the dimethyl ester ofα-methylhexafluoroisopropylphosphonic acid, while the analogous triethoxyphosphorane loses ethyl fluoride and yields the diethyl ester of pentafluoroisopropenylphosphonic acid. In this case, unstable adducts are formed as intermediates.

Valence-bond isomer chemistry. Part 11 [1]. Thermal rearrangement of the Diels-Alder adduct of hexafluorobicyclo-[2.2.0]hexa-2,5-diene and 2,3-Dimethylbuta-1,3-diene: a [1,3] sigmatropic shift of fluorine

Flow pyrolysis of the Diels-Alder adduct of hexafluorobicyclo[2.2.0]hexa-2,5-diene and 2,3-dimethylbutadiene gives an unusual product, the Diels-Alder adduct of hexafluorobenzene and 2,3-dimethylbuta-1,3-diene, and thence via an exclusive [1,3] sigmatropic fluorine shift, its isomeric triene. Loss of hydrogen fluoride from the unusual Diels-Alder adduct readily affords 1,2,3,4-tetrafluoro-6,7-dimethylnaphthalene.

Enamel fluoride uptake from orthodontic cements and its effect on demineralization.

This study was undertaken to determine the in vitro enamel fluoride uptake and distribution from fluoride-containing orthodontic cements after 21 days' exposure and the effect on acid demineralization. Three successive acid-etch biopsy specimens were taken from tne facial middle third of thirty maxillary central incisors. Orthodontic bands were cemented to these teeth, ten each with (A) zinc phosphate, (B) zinc phosphate containing 5 percent SnF2, and (C) silicophosphate cement, respectively. The teeth were suspended individually in synthetic saliva at 37 degrees C. in a shaking incubator for 21 days. The bands were removed, the cement was cleaned off, and three successive biopsies were carried out electrometrically and for calcium by atomic absorption spectroscopy. Fluoride concentrations were adjusted to depths of 10.0, 20.0, and 30.0 micron for the three biopsies, respectively. The acquired fluoride was calculated and the data were analyzed statistically. In addition, six teeth each with bands cemented with cements A, B, and C, respectively, were incubated in synthetic saliva for 21 days, after which the bands were loosened and the teeth were suspended for a further 3 months in a caries-producing medium. After careful cleaning, the enamel surfaces were examined by microradiography and scanning electron microscopy for demineralization. Results showed that acquired fluoride at the first depth was highest with cement C, followed by cement B, with cement A producing a net loss of fluoride. Further, the greater the fluoride uptake, the more resistant the enamel was to demineralization.

ChemInform Abstract: THERMAL REACTIONS OF THE MIXED‐VALENCE IRON FLUORIDES, FE2F5.NH2O

AbstractAnhand kombinierter thermogravimetrischer, differentialthermogravimetrischer und differentialscanningkalorimetrischer Untersuchungen läßt sich zeigen, daß die beginnende Dehydratisierung von FezFs ° 7 H2O bei 100°C ein komplexer Prozeß ist, der zu einer Fluoridmangelphase der nominellen Zusammensetzung FezFs ° 2 H2O führt.

Thermal reactions of the mixed-valence iron fluorides, Fe2F5·nH2O

The thermal reactions of Fe2F5·7H2O and Fe2F5·2H2O have been studied using a combination of thermogravimetric and differential thermogravimetric analysis and by differential scanning calorimetry. The initial dehydration of Fe2F5·7H2O near 100 °C is shown to be a complex process which leads to a fluoride-deficient phase of nominal composition Fe2F5·2H2O. Further heating leads to a product at the hemihydrate level. Isothermal dehydrations lead to two distinct high-temperature phases, but the formation of these materials is accompanied by both oxidation and fluoride loss. Vacuum dehydration of Fe2F5·7H2O leads to a fully mixed-valence monohydrate phase, which was previously prepared by dehydration in an HF atmosphere. Dehydration of the authentic crystalline Fe2F5·2H2O is seen to the distinguishable from the second-stage dehydration of Fe2F5·7H2O. Thermogravimetric analyses, thermodynamic measurements, and the kinetic parameters extracted from the several thermal techniques demonstrate that these two forms of ‘Fe2F5·2H2O’ differ significantly in their thermal reactions.

The reduction of fluorine-containing triarylmethanols by formic acid

Triarylmethanols containing one or more fluorine substituents in the para-positions are converted by 90% formic acid into a mixture of the fluorine-containing triarylmethane, and a second component in which one fluorine has been replaced by a hydroxy-group. A mechanism is proposed which involves nucleophilic attack by water on the initial carbonium ion (4) with subsequent loss of hydrogen fluoride, to give the diphenyl-p-hydroxyphenylmethyl carbonium ion (6) which undergoes hydride transfer with formate to give the product. This mechanism was supported by the isolation of 4-hydroxytriphenylmethanol from the reaction involving 4-fluorotriphenylmethanol. Pentafluorophenyldiphenylmethanol on similar treatment gave 9-(pentafluorophenyl)fluorene, and 2-(trifluoromethyl)triphenylmethanol gave 9-(2-trifluoromethylphenyl)fluorene. Both reactions presumably occur via an intramolecular electrophilic aromatic substitution. The 19F and 13C n.m.r. spectra of the triarylmethanes and 9-arylfluorenes are reported and discussed.

21—THE HYDROLYSIS OF FLUOROZIRCONATE ON WOOL

An investigation is reported in which the extensive loss of fluoride on the laundering of fluorozirconate-treated wool is confirmed by using a pyrohydrolysis-analysis method. Fluoride is not necessary for adequate flame-retardance, but, at low fluoride levels (i.e., F/Zr ratio less than 2), the formation of a complex between zirconium and the carboxyl groups of wool is necessary. The burning behaviour of an esterified fluorozirconate-treated sample is adversely affected as fluoride is lost because a carboxyl complex cannot be formed. Zirconium dioxide itself is ineffective as a flame-retardant for wool.

Electron energy loss of hydrogen fluoride

A 70 eV electron energy loss spectrum for the molecule HF is reported, in the range 11-16 eV. The v1 Sigma + valence state and two Rydberg series, each containing extensive vibrational structure are analysed.

Loss of fluoride during tablet production

Loss of fluoride during tablet production

Effect of fluoride tablets on uptake and loss of fluoride in superficial enamel in vivo.

The effect of tablets as a mode of fluoride administration was studied in vivo in short-term experiments. Small enamel sections were fixed in the oral cavity of volunteers with acry

The reactions of phosphorus fluorides with lithium bis-trimethylsilylamide

The reactions of phosphorus trifluoride, thiophosphoryl trifluoride, phosphorus oxytrifluoride, and phosphorus pentafluoride with lithium bis-(trimethylsilyl)amide have been studied. In hexane, phosphorus trifluoride and thiophosphoryl trifluoride react to give F 2PN(SiMe 3) 2 and F 2P(S)N(SiMe 3) 2 respectively with the loss of lithium fluoride, whereas phosphorus oxytrifluoride and phosphorus pentafluoride react to give LiN(P(O)F 2) 2 and LiN(PF 4) 2 respectively and trimethylsilyl fluoride. The i.r. and 31P and 19F spectra are reported for all products.

Fluoride incorporation into developing enamel of permanent teeth in the domestic pig

The young domestic pig affords a model for comparing fluoride levels in developing enamel, both within one tooth and within the entire permanent dentition. A preliminary study in a 7-month old control pig showed a significant inverse correlation between the mean fluoride concentration, expressed as μgF/cm 3 enamel and density of enamel in different teeth, but within any one tooth there was less consistency in this pattern. The fluoride results, when viewed with protein and phosphorus results, suggest an absolute loss of fluoride as enamel becomes fully mineralised. To examine whether the incorporation of ingested fluoride occurs at a particular stage in the development of enamel, three female litter-mates were fed a basic diet (containing 8 ppm F. equivalent to a daily intake of about 0.25 mg F/kg body weight) from 4-months of age. A control pig was killed when 4 1 2 - months old . The others received a daily dietary supplement of 0.25 mg F/kg body wt, as a sodium fluoride solution, one from 4 1 2 to 6 months of age, the other from 6 to 7 1 2 months . Analysis showed that as each tooth type matured the mean enamel fluoride content fell, but the fluoride figures in the pigs receiving F-supplement did not reflect the additional fluoride intake, probably because the critical period for incorporation preceded or followed the period of fluoride administration or that measurement of fluoride in whole bulk enamel failed to detect any surface accumulation.

12—THE COMPOSITION OF FLUOROZIRCONATES AND FLUOROTITANATES ON WOOL

The composition of fluorine–zirconium species on wool is dependent on the method of exhaustion. The limiting-oxygen index (LOI) of wool is not influenced by small amounts of zirconium, but, above about 0.4% zirconium (o.w.f.), there is a linear increase of LOI with zirconium content up to a maximum value. It is confirmed that fluorozirconates and fluorotitanates on wool undergo extensive loss of fluoride on laundering.

Schistosoma mansoni: Defined system for stepwise transformation of cercaria to schistosomule in vitro

Defined conditions are described for the in vitro production of large numbers of tail-free viable schistosomules. These consist of (1) the centrifugation of cold cercarial suspension and the incubation of the packed cercariae in a minimal volume of medium at 30 C for 40 min to effect tail loss and glandular secretion; (2) the isolation of the bodies by resuspension and sedimentation and (3) the induction of surface changes by incubating the bodies in inactivated serum or a defined tissue culture medium for a further 40 min interval at 37 C with mild agitation. The resultant schistosomules are characterized by the depletion of their penetration gland contents, loss of tail, fluoride and water sensitivities, complement insensitivity, negative “Cercarien-hüllen Reaktion,” and loss of the surface coat as demonstrated by periodic acid-Schiff (PAS) staining and electron microscope observations.

The thermal decomposition of ammonium hexafluorogallate and ammonium hexafluoroindate. New crystalline forms of gallium fluoride and indium fluoride

Ammonium hexafluorogallate, (NH4)3GaF6, and ammonium hexafluoroindate, (NH4)3InF6, occur in two polymorphic forms, a low temperature tetragonal and a high temperature cubic form, which transform reversibly. They decompose on heating with an initial loss of 2 moles of ammonium fluoride, forming ammonium tetrafluorogaIlate, NH4GaF4, and ammonium tetra fluoroindate, NH4InF4. Further heating results in the gradual loss of ammonium fluoride; the final decomposition products are γ-gallium fluoride and γ-indium fluoride, new crystalline forms. These convert on further heating to the common hexagonal forms of the trifluorides. The structural relationship of the compounds are discussed and compared with those of the aluminum analogs.

The loss of topically applied fluoride from the surface of human enamel in vitro, using 18F

The loss of fluoride from human enamel treated with acidulated phosphate-fluoride, sodium fluoride, and stannous fluoride was studied. The results suggested that the loss of fluoride could be a diffusion process, accompanied by simultaneous chemical reaction. No difference in pattern of loss was noted after using the different solutions.

Incorporation of fluoride by human enamel. 3. In vivo effects of nonfluoride and fluoride prophylactic pastes and APF gels.

Prophylactic procedures with a nonfluoride paste decrease the enamel surface fluoride concentration, whereas a sodium fluoride paste tends to prevent this loss. Topical acidulated phosphate-fluoride gel treatments exceed the equilibrium of enamel fluoride concentrations that are obtained subsequently by a second-order fluoride loss reaction.

Mobilization of fluoride from the bones and teeth of growing and mature rats

Fluoride was deposited at somewhat similar rates in the various bones of the growing rat receiving 10 ppm F for 70 days. During a subsequent 350 day post-fluoride period comprised of five 10-week intervals, total fluoride loss averaged about 9 per cent in the edentulous skeleton, and approximately 90 per cent of the loss occurred during the first 10-week post-fluoride period. The percentage loss in total fluoride during this same period varied from 2.3 per cent to 14.3 per cent for the various bones. The molars showed little if any change, and the incisors lost almost all the fluoride previously deposited. The anomalous increase of fluoride in the ventral rib and to a lesser degree in the pes + manus, was interpreted to indicate the possibility of local translocation of fluoride. The rate of deposition of fluoride in the various bones of the mature rat after 365 days on the fluoride regimen was essentially similar except for the ventral rib and the bones of the hand and foot which showed a slower rate of fluoride deposition. Mobilization of fluoride from skeletal components of the rats receiving 10 ppm F for 365 days was more variable than in the growing rat and rose progressively during three 10-week post-fluoride periods to 10 per cent of the previously deposited fluoride. The molar teeth, vertebra, humerus, ulna + radius, dorsal rib and the pes + manus showed less than a 10 per cent change in fluoride. The remaining bones mobilized between 14 and 18 per cent of the fluoride deposited at the end of the 365-day fluoride administration period. The incisors lost about 90 per cent of their fluoride. Various bones of the rat grew at quite different rates. For example, the ventral rib doubled in dry, fat-free weight between 70 and 420 days on experiment, whereas the bones of the hand and foot increased by only some 18 per cent. The rate of mineralization also varied considerably between bones.