Absence Of Fluoride Research Articles

Fluoride–Dependent Formation of Mineralized Layers in Bovine Dentin during Demineralization in vitro

Demineralization of dentin in the presence of fluoride produces lesions with a mineralized surface layer which becomes thicker and more mineralized with higher fluoride concentrations whereas the lesion depth is hardly affected. The aim of this study was to investigate the effects of the time of fluoride treatment and the amount of fluoride taken up on the properties of the mineralized layer. Discs of bovine dentin embedded in methylmethacrylate with one surface exposed were demineralized in 50 mM acetic acid, 2.2 mM CaCl₂, 2.2 mM KH₂PO₄, pH 5.0. At the start and/or later during the demineralization period, the specimens were incubated individually for 1 or 2 days in 10 ml of the same demineralization solution supplemented with 0.5, 2.0 or 5.0 ppm fluoride, which was then assessed for changes in calcium and fluoride concentrations. After 2, 5 and 8 days, specimens were sectioned for microradiographic analysis so as to follow development of the lesions and the mineralized layers. The results were the following: While demineralization with fluoride present at the first day led to the formation of a surface layer, fluoride present only at a later day produced a subsurface layer, not at the lesion front but closer to the surface. This layer resulted from (re)precipitation and not from preservation of the original mineral. The 'integrated mineral content' of the surface layer increased linearly with the uptake of fluoride, which resulted in an apparent fluorapatite content of about 20 vol%. The profiles of the surface layers remained unchanged during continued demineralization in the absence of fluoride. It was concluded that in the presence of fluoride mineral loss is reduced as a result of the reprecipitation of dissolved mineral ions as a layer of fluoride–enriched apatite. This layer does not offer protection of underlying dentin against continued demineralization.

Structural analysis of proteoglycans synthesized by mineralizing bone cells in vitro in the presence of fluoride.

This study investigated the biochemical structure of proteoglycans synthesized during matrix maturation by mineralizing bone cells in vitro, in the presence and absence of fluoride. Bone cells were obtained from rat femur washes and cultured in alpha MEM media supplemented with fetal calf serum, ascorbic acid, beta-glycerophosphate and dexamethasone. Cells were characterized as osteoblast-like by the expression of alkaline phosphatase activity and the synthesis of collagen type I and osteocalcin. Fluoride, present in the culture media at concentrations of 10(-5) M or 10(-7) M, had negligible effect on cell viability. However, calcium deposition was increased in cell cultures incubated in the presence of fluoride. Proteoglycans were extracted from the extracellular matrix with 4 M guanidinium chloride and purified by anion exchange chromatography. Biochemical analysis identified the presence of the small leucine rich proteoglycan, decorin and biglycan, in addition to degradation products relating to the larger chondroitin sulphate protoeglycan, versican. Fluoride had little effect on the size or amino acid composition of the protein core, but resulted in significant alterations to the GAG chains, including a dramatic reduction in chain length, reduction in sulphation and decrease in the proportion of dermatan sulphate compared to chondroitin sulphate. The influence of fluoride on proteoglycan structure synthesized by mineralizing bone cells provides valuable information, indicating specific roles for dermatan sulphate and chondroitin sulphate proteoglycans. The results suggested that fluoride affected the post-translational assembly of the GAG chains which may be an influential factor in the mineralization process.

Protective effect of hexetidine against in vitro bacterial demineralisation of bovine enamel and dentin in the presence of fluoride.

Bovine enamel and dentin specimens were overlaid with acidogenic Streptococcus mutans suspensions in agarose. In this model, the minimal demineralisation-inhibiting concentrations (MDIC) of hexetidine was determined in the presence of fluoride. A commercially available mouthwash containing 0.1% (2.9 mmol/l) hexetidine was diluted serially and added to the bacterial suspensions together with 0, 5.3, or 26.3 mumol/l fluoride (NaF). After 22 h of incubation at 37 degrees C the bacterial suspensions were removed and assessed for calcium and lactate. The results showed significant inhibitory effects of hexetidine on the demineralisation of the enamel specimens with a MDIC between 15 and 31 mumol/l hexetidine. In the presence of fluoride, approximately fourfold higher concentrations of hexetidine were needed for a significant additional protection of the enamel. No synergistic effect between hexetidine and fluoride was observed. For the demineralisation of the dentin specimens, the MDIC of hexetidine had a value between 31 and 61 mumol/l. At both these concentrations the dentin specimens were relatively less protected in the presence than in the absence of fluoride, and some synergistic effect between hexeditine and fluoride was observed.

Fluoride at mitogenic concentrations increases the steady state phosphotyrosyl phosphorylation level of cellular proteins in human bone cells.

This study was designed to test the hypothesis that treatment of human bone cells with mitogenic concentrations of fluoride would lead to an increase in the steady state level of tyrosyl phosphorylation of specific cellular proteins. With an immunoblot assay method, it was found that mitogenic concentrations of fluoride (i.e. 50-200 mumol/L) induced a dose- and time-dependent increase in the level of tyrosyl phosphorylation of at least 13 cellular proteins in both normal human bone cells and human TE85 osteosarcoma cells. Time-course studies revealed that a statistically significant increase in tyrosyl phosphorylation of these 13 cellular proteins in human bone cells was observed after 3-6 h of fluoride treatment and was sustained for up to 24 h. This time course was not compatible with a direct activation of tyrosyl kinases, as epidermal growth factor, which activates tyrosyl kinase activity, induced an immediate and acute response that was rapidly reversible within 1 h. Although fluoride increased the steady state tyrosyl phosphorylation of the cellular proteins in human bone cells, the same micromolar doses of fluoride had no effect on human skin fibroblasts, which are fluoride-nonresponsive cells. The effects of fluoride were rapidly reversible in the absence of fluoride and could be acutely potentiated by pretreatment with epidermal growth factor. In summary, we have shown for the first time that mitogenic concentrations (i.e. 50-200 mumol/L) of fluoride increased the steady state level of tyrosyl phosphorylation of at least 13 cellular proteins in human bone cells, and that the increases were relatively show in onset and sustained. In conclusion, these findings are consistent with the hypothesis that the osteogenic actions of fluoride are mediated at least in part by an inhibition of the activity of one or more fluoride-sensitive phosphotyrosyl protein phosphatases in human bone cells.

The Role of Cation Bridging in Microbial Fluoride Binding

The cation-bridged fluoride binding model proposed previously was tested by measuring fluoride binding to Streptococcus mutans R9 in the presence and absence of calcium, magnesium or zinc ions. The dissociation constant for fluoride binding to washed cells was 8.4 +/- 7.9 mmol/l and the binding capacity was 4.3 +/- 1.7 mumol/g wet weight. Binding was largely accounted for by residual bound divalent magnesium, with a small contribution from calcium. In the presence of 5 mmol/l divalent cation, dissociation constants for fluoride (mmol/l) were: 12.2 +/- 3.8 (calcium), 9.9 +/- 0.4 (magnesium) and 14.4 +/- 0.5 (zinc). Binding capacities (mumol/g wet weight) were: 122 +/- 26 (calcium), 130 +/- 90 (magnesium) and 142 +/- 56 (zinc). Fluoride produced a marked reduction in calcium binding affinity and approximately doubled the calcium binding capacity. In the absence of fluoride, divalent cation binding to plaque is bidentate. It is suggested that fluoride, by competing with macromolecular anionic groups, causes binding to become monodentate. This allows the binding of double the quantity of cations (and of further fluoride). Release of fluoride, bound by calcium bridging, into plaque fluid, as a result of fluoride clearance into saliva, or of a fall in pH, will always be accompanied by a release of calcium which will potentiate the cariostatic effect of fluoride.

Caries-Preventive Effects of Fluoride-Releasing Materials

The plaque-retentive properties of fixed orthodontic appliances result in a severe challenge on surfaces generally not susceptible to caries. Lesions may develop within a month in the absence of fluoride, and clinical studies have shown that from 50 to 75% of orthodontic patients develop decalcifications on labial surfaces during treatment. Fluoride mouthrinses reduce the occurrence, although compliance is often poor. Orthodontic bonding agents and cements releasing fluoride, which reduce the need for cooperation, have been introduced. Few clinical studies have been done to prove the cariostatic properties of fluoride-releasing materials in orthodontics. In short-term caries model studies, glass ionomers and a glass filler containing light-cured adhesive that releases relatively large amounts of fluoride have shown cariostatic properties. However, during severe challenges such as occur with orthodontic appliances, fluoride alone has limited cariostatic properties. The combination of fluoride with antimicrobial agents, and the use of acidic fluoride solutions depositing acid-resistant coatings of calcium fluoride and titanium have shown to give better clinical effects than fluoride alone during extreme conditions. Fluoride-releasing materials may therefore be considered as useful supplements to these procedures.

The tooth as a marker of developing world quality of life: A field study in Guatemala

A geographical sample in a rural area of eastern Guatemala revealed widespread, premature and heavy losses of permanent teeth. Social and environmental influences that affect tooth loss include inadequate diet, refined sugar, poor oral hygiene, absence of fluoride, lack of preventive education and insufficiency of dental care services. Land hunger and family poverty are of paramount importance. Gender-based cultural differences are apparent in tooth extraction rates, and use of dentures. No one escapes visitations of severe orofacial pain that cast a blight upon the quality of rural life. Periodontal disease drives the poorest of the poor to spend disproportionately large sums on pharmaceutical pain-killers and destructive traditional medicines. Lay ‘tooth-pullers’ visit remote rural homes to extract teeth. Only full edentulism can bring patients permanent somatic and financial relief. Community dental health is conspicuously neglected in official policies and plans for rural development.

Corrosion of nickel—chromium deposit on AISI 316L stainless steel in radioactive water with and without fluoride at pH 4

The electrochemical behavior of samples was studied using potentiodynamic techniques at low scan rates, cyclic voltammetry at high scan rates and electrochemical impedance spectroscopy. The surfaces were examined and analyzed by scanning electron microscopy and X-ray microanalysis, respectively. The results from these different methods are discussed. They show that the deposit is more easily corroded than the AISI 316L stainless steel in presence or absence of fluoride. With fluoride and at the prepassive potentials, the Warburg straight line indicates that there is ionic diffusion in the nickel—chromium deposit oxide. The equivalent circuits for the nickel-chromium are proposed and indicate that the deposit can take part in localized corrosion. The use of high scan rates shows the transient kinetics of the oxide formation in presence of fluoride. With fluoride, the pitting currents are higher for nickel-chromium deposits. The SEM photographs and polarization curves show that the NiCr deposit is locally corroded by fluoride, leading to the possibility of crevice formation under this and in 316L stainless steel.

Effect of low levels of fluoride on calcium uptake by demineralized human enamel

The effect of fluoride ( ca. 0.1 parts/10 6) on calcium uptake by enamel was examined under alternating remineralizing and demineralizing conditions. The remineralizing solutions contained either 0, 0.058, 0.104 or 0.138 parts/10 6 fluoride (ex NaF), while the demineralizing solutions contained no added fluoride. During the demineralization periods, calcium loss was similar for all groups. However, during the remineralizing periods, all levels of added fluoride were found to promote calcium uptake. Calcium levels taken up by the artificial lesions were found to increase with increasing fluoride concentration in solution, and were independent of surface area of exposed enamel. In the absence of fluoride, even under conditions that are considered to be remineralizing, further demineralization took place.

Physical model for lesion formation in the presence of low levels of solution fluoride

A quantitative physical model is presented for the formation of subsurface carious lesions in the presence of low levels of solution fluoride. Calculations using independently determined model parameters are in agreement with mineral density profiles measured in bovine enamel lesions. The proposed mechanism is controlled by fluoride in the following way: as fluoride diffuses into enamel, it is rapidly adsorbed to enamel crystallites, resulting in very low microenvironmental fluoride concentrations, so long as the crystals are not saturated with respect to fluoride adsorption. The result of this saturable adsorption is a widening band of fluoride-saturated crystals near the surface, beneath which the microenvironmental fluoride concentrations are negligible. In the saturated band, the microenvironmental fluoride concentration in the pore solution is high enough to suppress dissolution, while in the deeper, relatively fluoride free region, dissolution can occur. In addition to predicting observed mineral density profiles, the model also predicts the demarcation in solution conditions between the regime where subsurface lesion formation occurs and that where the dissolution pattern is that of surface erosion; and the lack of insensitivity of dissolution rate to hydrodynamics in the presence of low levels of fluoride, as contrasted to the square root of stirring rate dependency observed in the absence of fluoride.

Evolution of fluoride tolerance in Plantago lanceolata

Fluoride tolerance evolution was investigated by means of simple solution culture experiments. Seeds of Plantago lanceolata were collected at different distances from a fluoride manufacturing works and germinated in Petri dishes. A previous study had demonstrated an exponential type decrease in soil fluoride concentrations with distance from the factory. Plants grown from seeds collected near the factory were slower growing than susceptible plants in the absence of fluoride, but faster growing in the presence of fluoride. This is the first study providing evidence of fluoride tolerance in plants. As in studies demonstrating tolerance to other pollutants, tolerance evolution seems to involve a ‘cost’ in terms of a lower productivity of tolerant compared with non-tolerant plants.

Target-promoted alkylation of DNA.

Inducible and selective alkylation of DNA was accomplished under neutral conditions by use of a silyl-protected phenol that served as a precursor for a highly reactive quinone methide. As expected, addition of fluoride triggered reaction of a model compound, 3-(tert-butyldimethylsiloxy)-4-[(p-nitrophenoxy)methyl]benzamide, and its oligodeoxynucleotide conjugate. Surprisingly, the silyl phenol was also specifically yet more slowly activated by the environment of duplex DNA in the absence of fluoride. This alternative process was associated with the hybridization of probe and target strands, and single-stranded DNA was unable to induce a similar activation. Therefore, DNA appears to effect its own alkylation by promoting the formation of an electrophilic and nondiffusible intermediate.

Chloroplast thylakoid protein phosphatase reactions are redox-independent and kinetically heterogeneous

At least eleven thylakoid proteins become phosphorylated under reducing conditions, and redox titration has identified a common midpoint potential of E m = +38 ± 4 mV, n = 0.95 ± 0.06. In the presence of the phosphatase inhibitor NaF (10 mM), the redox dependency of phosphorylation is found to be essentially unchanged: E m = +50 ± 3 mV, n = 1.02 ± 0.04. Thylakoid membranes were phosphorylated in the light and then incubated at various redox potentials for 15 min in the dark; no redox dependency was observed in the dephosphorylation of any of the 17 bands then distinguishable by autoradiography and phosphorimaging. The phosphoprotein phosphatase reactions can be divided arbitrarily into four kinetic classes: the fastest, class I, includes LHC II; the moderate class II includes D1 and D2; the slow class III includes CP43 and the 9 kDa phosphoprotein; finally, a 19.5 kDa protein exhibited no loss of 32P at all. In separate experiments we measured thylakoid protein dephosphorylation initiated by changing the redox potential from −140 to +200 mV, in the presence or absence of fluoride. In this case the results are consistent with at least two kinetically distinguishable classes of phosphoprotein phosphatase reactions. We conclude that thylakoid protein phosphatase reactions are kinetically heterogeneous and redox-independent. It follows that the redox dependency of thylakoid protein phosphorylation is a property of thylakoid protein kinase reactions. Our observed E m and n values are consistent with a primary site of kinase redox control at the level of PQ/PQ .− of the Q i (Q n) site of the cytochrome b 6/ƒ complex.

Initial dissolution rate studies on dental enamel after CO2 laser irradiation.

The influence of CO2 laser irradiation on the dissolution behavior of human dental enamel has been investigated. Human enamel was irradiated by a continuous-wave CO2 laser at 10.6 microns and initial dissolution rates (IDRs) were measured in 0.1 mol/L acetate buffer, pH = 4.5, both with and without calcium and/or phosphate common ion, by means of a rotating disk assembly. The effects of (1-hydroxyethylidene) bisphosphonic acid (EHDP), fluoride (F), and dodecylamine HCl (DAC) at various levels upon the IDR were also determined. All of the findings were consistent with the hypothesis that CO2 laser irradiation converts dental enamel to hydroxyapatite (HAP) possessing site #2 character (Yamamoto et al., 1986). The dissolution driving force function, KHAP = aCa10aPO4(6)aOH2, was found to have a value of 10(-129.9) after being lased, as compared with 10(-121.4) before being lased. The IDR values for EHDP (3 mmol/L) and DAC (3 mmol/L) were essentially zero as expected for site #2 HAP. For solution F, the deduced dissolution driving force function, KFAP = aCa10aPO4(6)aF2 was 10(-128.6) after being lased as compared with 10(-116.3) before being lased. These results all support the hypotheses (1) that laser irradiation may convert the surface of human dental enamel to an apatite of significantly lower effective solubility (i.e., site #2 HAP) than that of unlased enamel; and (2) that there is significant synergism between laser treatment and these chemical dissolution rate inhibitors (again consistent with site #2 HAP). Simple model calculations indicate that, in both the presence and absence of fluoride, these laser-induced changes in the driving force for dissolution should dramatically lessen the susceptibility of enamel to the types of acid challenge that might be encountered in the mouth.

An in situ model for simultaneous assessment of inhibition of demineralization and enhancement of remineralization.

In situ models to assess the ability of oral care products or food components to enhance remineralization and/or inhibit demineralization of tooth enamel or roots must be very carefully designed to minimize the confounding effects of the many variables involved. Controlling these variables as closely as possible is essential if meaningful answers are to be obtained from the models. We have developed an in situ model which combines the experience of several groups. Detailed screening of subjects is essential. Selection criteria should include good general health, good dental health, mandibular partial denture, at least eight natural teeth, no active caries lesions, known fluoride history, normal salivary function, and no medications that affect salivary function. Each subject carries a sound enamel slab and an enamel slab with a pre-formed caries-like lesion (demineralized in vitro) in his/her denture on each side of the mouth for test periods of two or four weeks. The demineralization challenge is controlled by extra-oral immersion of the appliances in sucrose daily. Daily product exposure or daily food component exposure is used as desired. Compliance indicators and a diet diary are included. Whole saliva flow rate (unstimulated), plaque acidogenicity, and salivary fluoride are monitored during the test periods. At the end of the test period, the test slabs are assessed for mineral change, after being sectioned, by means of cross-sectional microhardness or microradiography. The mineral loss or gain (delta M, microns x vol%), compared with adjacent control sections retained in the lab, is calculated as change in delta Z (microns x vol%), namely, delta M = delta ZTEST - delta ZCONTROL.(ABSTRACT TRUNCATED AT 250 WORDS)

The in vivo orthodontic banding model for vital teeth and the in situ orthodontic banding model for hard-tissue slabs.

This paper presents the orthodontic banding model for vital teeth and the orthodontic in situ model for slabs of enamel, root surface, dentin, or other mineralized tissues such as shark enamel. The model for vital teeth is an in vivo model, since a crevice for plaque accumulation is created behind orthodontic bands on the buccal enamel surfaces of teeth in situ. Visible white-spot lesions are usually seen after a four-week banding period in the absence of fluoride. The microbiological flora developed behind the bands shows a similarity to that of natural caries. Microradiographic data show that the initial lesion is a softening of the enamel surface. Later, a subsurface lesion develops. A modification of the model has been developed for the use of slabs of mineralized tissues. In this model, slabs are mounted on a removable appliance. The slabs are covered with orthodontic banding material for plaque accumulation. Lesion development in enamel in the two model systems is almost identical. The benefit of the in vivo model is that caries development can be studied on vital teeth in young individuals. The model is independent of the patient's cooperation. No special diet is required, e.g., no sucrose rinsing. In the in situ model, slabs could be examined after one study period and then replaced for another period.

The effect of fluoride on photodynamic-induced fluorescence changes of aluminium phthalocyanine in Chinese hamster cells.

Fluence-dependent changes in the fluorescence of aluminium phthalocyanine (AlPc) were measured in Chinese hamster ovary (CHO) cells using digital fluorescence microscopy of single cells and spectrofluorimetry of cell suspensions. During illumination the fluorescence initially increased and later progressively decreased. In the presence of fluoride, which protects against phototoxicity of AlPc by forming a fluoroaluminium complex, there was no initial increase in fluorescence: it decreased about 10 times faster than in the absence of fluoride. Qualitatively similar results were observed using single-cell fluorescence microscopy, which also showed the dye to be mostly localized in cytoplasmic organelles and membranes. The pattern of localization did not change during illumination. Concomitant assays of dye extracted from cells revealed little photodegradation that could not account for the fluorescence changes. The absorption spectra of AlPc-loaded cells showed some aggregation of the dye prior to light exposure. During illumination the dye was initially monomerized and subsequently progressively reaggregated. In the presence of fluoride no monomerization was seen, and the aggregation proceeded at a much faster rate. It is concluded that the fluorescence changes are not due to major relocalization of AlPc in the cells, but to light-induced monomerization followed by reaggregation. The protective effect of fluoride may be due to the enhanced aggregation rate, because aggregated dye molecules are photochemically inactive. Because D2(0) affects neither the initial enhanced fluorescence in the absence of fluoride nor the rapid decrease in its presence it appears that 1O2 is not involved in the photodynamic reactions leading to these changes.

Fluoride, beryllium and ADP combine as a ternary complex in aqueous solution as revealed by a multinuclear NMR study.

Different kinds of nucleotide binding enzymes are sensitive to fluoroberyllate complexes (BeFx) and fluoroaluminate complexes (AlFy). It has been hypothesized that the effects of these fluorometals are related to the generation at a nucleotide binding site of a pseudo nucleoside triphosphate, consisting of a fluorometal moiety bound to the beta phosphate group of a molecule of nucleoside diphosphate (Bigay et al. 1985; Lunardi et al. 1985). In order to establish whether ternary complexes comprising ADP, beryllium and fluoride can exist in slightly alkaline solution in the absence of enzyme, we have carried out a multinuclear (31P, 9Be and 19F) NMR study. In preliminary experiments, pyrophosphate (PPi) was substituted for ADP and taken as a simpler analog of nucleoside diphosphate. In the absence of fluoride, three types of PPi-Be complexes were generated: two of these were bidentate chelates with either one or two pyrophosphate molecules bound per beryllium; the third one was a monodentate complex. It is probable that the same types of combination exist between the polyphosphate chain of ADP and Be. In the presence of fluoride, both ADP and PPi combined with beryllium to form ternary complexes. These complexes consisted of monofluoroberyllate(-BeF) or difluoroberyllate(-BeF2) bound to the two phosphates of one molecule of ADP or PPi as a bidentate chelate. We failed to observe the formation of complexes between ADP and trifluoroberyllate(-BeF3). The relevance of this study to the biological effects of fluoride and beryllium on various enzymic reactions is discussed.

Inhibition of proton-translocating ATPases of Streptococcus mutans and Lactobacillus casei by fluoride and aluminum

One of the major effects of fluoride on oral bacteria is a reduction in acid tolerance, and presumably also in cariogenicity. The reduction appears to involve transport of protons across the cell membrane by the weak acid HF to dissipate the pH gradient, and also direct inhibition of the F1F0, proton-translocating ATPases of the organisms, especially for Streptococcus mutans. This direct inhibition by fluoride was found to be dependent on aluminum. The dependence on aluminum was indicated by the protection against fluoride inhibition afforded by the Al-chelator deferoxamine and by loss of protection after addition of umolar levels of Al3+, which were not inhibitory for the enzyme in the absence of fluoride. The F1 form of the enzyme dissociated from the cell membrane previously had been found to be resistant to fluoride in comparison with the F1F0 membrane-associated form. However, this difference appeared to depend on less aluminum in the F1 preparation in that the sensitivity of the F1 enzyme to fluoride could be increased by addition of umolar levels of Al3+. The effects of Al on fluoride inhibition were apparent when enzyme activity was assayed in terms of phosphate release from ATP or with an ATP-regenerating system containing phosphoenolpyruvate, pyruvate kinase, NADH and lactic dehydrogenase. Also, Be2+ but not other metal cations, e.g. Co2+, Fe2+, Fe3+, Mn2, Sn2+, and Zn2+, served to sensitize the enzyme to fluoride inhibition. The differences in sensitivities of enzymes isolated from various oral bacteria found previously appeared also to be related to differences in levels of Al.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluoroacetate Production by Dichapetalum cymosum

Summary Field-grown Dichapetalum cymosum plants which appeared normal were invariably found to be infested with bacteria. It has not yet been ascertained whether the bacteria can synthesize fluoroacetate but seedlings of D. cymosum, when grown from surface sterilized seed in an aseptic environment, appear to synthesize fluoroacetate. A callus culture of D. cymosum was established which appears to be internally devoid of microorganisms. The culture grows well in the absence of fluoride and then does not contain fluoroacetate. Fluoride (0.78–6.24 mM) does not affect the growth of the callus but results in the production of up to 1227 mg fluoroacetate per kg fresh callus.