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Nanoparticles have been recognized as promising tools for targeted drug-delivery and protein therapeutics. However, the mechanisms of protein-nanoparticle interaction and the dynamics underlying the binding process are poorly understood. Here, we present a general methodology for the characterization of protein-nanoparticle interaction on a molecular level. To this end we combined biophysical techniques including nuclear magnetic resonance (NMR), circular dichroism (CD), resonance energy transfer (RET) and surface plasmon resonance (SPR). Particularly, we analyzed molecular mechanisms and dynamics of the interaction of CaF 2 nanoparticles with the prototypical calcium sensor calmodulin (CaM). We observed the transient formation of an intermediate encounter complex involving the structural region linking the two domains. Specific interaction of CaM with CaF 2 NPs is driven by the N-terminal EF-hands, which seem to recognize Ca 2+ on the surface of the nanoparticle. We conclude that CaF 2 NP-CaM interaction is fully compatible with potential applications in nanomedicine. Overall, the methods presented in this work can be extended to other systems and may be useful to quantitatively characterize structural and dynamic features of protein-NP interactions with important implications for nanomedicine and nano-biotechnology.

This study evaluated if Carbon dioxide (CO2) (λ 10.6 μm) laser irradiation combined with acidulated phosphate fluoride gel application (APF gel) enhances "CaF2" uptake by demineralized enamel specimens (DES) and inhibits enamel lesion progression. Thus, two studies were conducted and DES were subjected to APF gel combined or not with CO2 laser irradiation (11.3 or 20.0 J/cm(2), 0.4 or 0.7 W) performed before, during, or after APF gel application. In study 1, 165 DES were allocated to 11 groups. Fluoride as "CaF2 like material" formed on enamel was determined in 100 DES (n = 10/group), and the surface morphologies of 50 specimens were evaluated by scanning electron microscopy (SEM) before and after "CaF2" extraction. In study 2, 165 DES (11 groups, n = 15), subjected to the same treatments as in study 1, were further subjected to a pH-cycling model to simulate a high cariogenic challenge. The progression of demineralization in DES was evaluated by cross-sectional microhardness and polarized light microscopy analyses. Laser at 11.3 J/cm(2) applied during APF gel application increased "CaF2" uptake on enamel surface. Laser irradiation and APF gel alone arrested the lesion progression compared with the control (p < 0.05). Areas of melting, fusion, and cracks were observed. CO2 laser irradiation, combined with a single APF application enhanced "CaF2" uptake on enamel surface and a synergistic effect was found. However, regarding the inhibition of caries lesion progression, no synergistic effect could be demonstrated. In conclusion, the results have shown that irradiation with specific laser parameters significantly enhanced CaF2 uptake by demineralized enamel and inhibited lesion progression.

Biofilm formation on the tooth surface is the root cause of dental caries and periodontal diseases. Streptococcus mutans is known to produce biofilm which is one of the primary causes of dental caries. Acid production and acid tolerance along with exopolysaccharide (EPS) formation are major virulence factors of S. mutans biofilm. In the current study, calcium fluoride nanoparticles (CaF2-NPs) were evaluated for their effect on the biofilm forming ability of S. mutans in vivo and in vitro. The in vitro studies revealed 89 % and 90 % reduction in biofilm formation and EPS production, respectively. Moreover, acid production and acid tolerance abilities of S. mutans were also reduced considerably in the presence of CaF2-NPs. Confocal laser scanning microscopy and transmission electron microscopy images were in accordance with the other results indicating inhibition of biofilm without affecting bacterial viability. The qRT-PCR gene expression analysis showed significant downregulation of various virulence genes (vicR, gtfC, ftf, spaP, comDE) associated with biofilm formation. Furthermore, CaF2-NPs were found to substantially decrease the caries in treated rat groups as compared to the untreated groups in in vivo studies. Scanning electron micrographs of rat's teeth further validated our results. These findings suggest that the CaF2-NPs may be used as a potential antibiofilm applicant against S. mutans and may be applied as a topical agent to reduce dental caries.

The chemical status of live sensory neurons is accessible with infrared microspectroscopy of appropriately prepared cells. In this paper, individual dorsal root ganglion (DRG) neurons have been prepared with two different protocols, and plated on glass cover slips, BaF2 and CaF2 substrates. The first protocol exposes the intact DRGs to 4 °C for between 20-30 minutes before dissociating individual neurons and plating 2 hours later. The second protocol maintains the neurons at 23 °C for the entire duration of the sample preparation. The visual appearance of the neurons is similar. The viability was assessed by means of trypan blue exclusion method to determine the viability of the neurons. The neurons prepared under the first protocol (cold exposure) and plated on BaF2 reveal a distinct chemical signature and chemical distribution that is different from the other sample preparations described in the paper. Importantly, results for other sample preparation methods, using various substrates and temperature protocols, when compared across the overlapping spectral bandwidth, present normal chemical distribution within the neurons. The unusual chemically specific spatial variation is dominated by a lack of protein and carbohydrates in the center of the neurons and signatures of unraveling DNA are detected. We suggest that cold shock leads to apoptosis of DRGs, followed by osmotic stress originating from ion gradients across the cell membrane leading to cell lysis.

The purpose of this study is to determine whether a calcium (Ca) prerinse used before a 228 µg/g (ppm) fluoride (F) rinse would induce the formation of 'calcium fluoride-like' (CaF2-like) deposits in human dental plaque. Sixty minutes after the use of the Ca prerinse/F rinse, plaque samples were collected from 10 volunteers, homogenized, and split into 2 aliquots. The plaque mass from one aliquot was then extracted with a 'plaque-like' solution that extracted all the CaF2-like deposits. The total F in both aliquots was then determined and compared. The results demonstrated that, as in previous studies, the Ca prerinse induced large increases in plaque fluid and total plaque F. However, unlike previous results without the Ca prerinse, 30% of the plaque F deposits were CaF2 or CaF2-like. Given that maintaining an elevated F concentration in the vicinity of a developing lesion may play an important role in the cariostatic effect of this ion, and the potential advantages of CaF2-like deposits as an F source, these results suggest that a Ca prerinse may increase the cariostatic effect of topical agents.

This study evaluated the synergy of professional acidulated fluoride gel (APF) or fluoridated dentifrice application combined with Er,Cr:YSGG laser irradiation on the formation of CaF2 -like products (CaF2 ), in vitro. Thus, 272 bovine enamel slabs were randomly distributed among eight groups: G1: untreated enamel; G2: treated with fluoridated dentifrice (NaF, 1,100 μgF/g); G3: treated with acidulated phosphate fluoride gel (APF, 1.23% F(-) ); G4: irradiated with Er,Cr:YSGG laser at 8.5 J/cm(2) ; G5 and G6: combination of pre-irradiation with Er,Cr:YSGG followed by dentifrice or APF application, respectively; G7: combination of dentifrice application followed by Er,Cr:YSGG irradiation; G8: combination of APF application followed by Er,Cr:YSGG irradiation. After treatments, samples were evaluated by scanning electron microscopy, and the content of CaF2 was determined by an ion specific electrode. Both APF and dentifrice application promoted the formation of CaF2 on enamel, whereas Er,Cr:YSGG irradiation promoted an increase of roughness of the enamel, increasing the surface area. Laser irradiation before fluoridated products increased the content of CaF2 formed when compared to groups that APF or dentifrice were applied isolated. However, the content of CaF2 formed when irradiation was performed after APF or dentifrice was not statically significant when compared to the control groups. In conclusion, Er,Cr:YSGG laser increases the formation of CaF2 on enamel when the irradiation is performed before the application of APF or dentifrice. The association of laser with APF is most promissory for caries prevention because of the higher concentration of CaF2 formation and also the chemical changes promoted by laser irradiation demonstrated in literature., (Copyright © 2013 Wiley Periodicals, Inc.)

Various authors have shown that the caries decline in the industrialized countries during recent decades is based on the use of fluorides, of which local fluoride application in the form of fluoridated toothpastes is of primary importance. The caries-protective potential of fluorapatite is quite low; in contrast, dissolved fluorides in the vicinity of enamel are effective both in promoting remineralization and inhibiting demineralization. Considering the fact that the caries decline occurred at the same time that local fluoridation measures became widely used, the conclusion seems justified that regular application of F⁻ can inhibit caries.

Current models for increasing the anti-caries effects of fluoride (F) agents emphasize the importance of maintaining a cariostatic concentration of F in oral fluids. The concentration of F in oral fluids is maintained by the release of this ion from bioavailable reservoirs on the teeth, oral mucosa and - most importantly, because of its association with the caries process - dental plaque. Oral F reservoirs appear to be of two types: (1) mineral reservoirs, in particular calcium fluoride or phosphate-contaminated 'calcium-fluoride-like' deposits; (2) biological reservoirs, in particular (with regard to dental plaque) F held to bacteria or bacterial fragments via calcium-fluoride bonds. The fact that all these reservoirs are mediated by calcium implies that their formation is limited by the low concentration of calcium in oral fluids. By using novel procedures which overcome this limitation, the formation of these F reservoirs after topical F application can be greatly increased. Although these increases are associated with substantive increases in salivary and plaque fluid F, and hence a potential increase in cariostatic effect, it is unclear if such changes are related to the increases in the amount of these reservoirs, or changes in the types of F deposits formed. New techniques have been developed for identifying and quantifying these deposits which should prove useful in developing agents that enhance formation of oral F reservoirs with optimum F release characteristics. Such research offers the prospect of decreasing the F content of topical agents while simultaneously increasing their cariostatic effect., (Copyright © 2011 S. Karger AG, Basel.)

Dental erosion develops through chronic exposure to extrinsic/intrinsic acids with a low pH. Enamel erosion is characterized by a centripetal dissolution leaving a small demineralized zone behind. In contrast, erosive demineralization in dentin is more complex as the acid-induced mineral dissolution leads to the exposure of collagenous organic matrix, which hampers ion diffusion and, thus, reduces further progression of the lesion. Topical fluoridation inducing the formation of a protective layer on dental hard tissue, which is composed of CaF(2) (in case of conventional fluorides like amine fluoride or sodium fluoride) or of metal-rich surface precipitates (in case of titanium tetrafluoride or tin-containing fluoride products), appears to be most effective on enamel. In dentin, the preventive effect of fluorides is highly dependent on the presence of the organic matrix. In situ studies have shown a higher protective potential of fluoride in enamel compared to dentin, probably as the organic matrix is affected by enzymatical and chemical degradation as well as by abrasive influences in the clinical situation. There is convincing evidence that fluoride, in general, can strengthen teeth against erosive acid damage, and high-concentration fluoride agents and/or frequent applications are considered potentially effective approaches in preventing dental erosion. The use of tin-containing fluoride products might provide the best approach for effective prevention of dental erosion. Further properly designed in situ or clinical studies are recommended in order to better understand the relative differences in performance of the various fluoride agents and formulations., (Copyright © 2011 S. Karger AG, Basel.)

Attenuated total reflectance infrared spectroscopy and complementary scanning electron microscopy were applied to analyze the surface structure of enamel apatite exposed to citric acid and to investigate the protective potential of fluorine-containing reagents against citric acid-induced erosion. Enamel and, for comparison, geological hydroxylapatite samples were treated with aqueous solutions of citric acid and sodium fluoride of different concentrations, ranging from 0.01 to 0.5 mol/L for citric acid solutions and from 0.5 to 2.0% for fluoride solutions. The two solutions were applied either simultaneously or consecutively. The citric acid-induced structural modification of apatite increases with the increase in the citric acid concentration and the number of treatments. The application of sodium fluoride alone does not suppress the atomic level changes in apatite exposed to acidic agents. The addition of sodium fluoride to citric acid solutions leads to formation of surface CaF2 and considerably reduces the changes in the apatite P-O-Ca framework. However, the CaF2 globules deposited on the enamel surface seem to be insufficient to prevent the alteration of the apatite structure upon further exposure to acidic agents. No evidence for fluorine-induced recovery of the apatite structure was found.

The aim of this study was to evaluate, using scanning electron microscopy (SEM), the calcium fluoride uptake by human enamel in situ after topical application using three fluoridated mouthrinses: a neutral pH solution (Fluordent), an acidulated solution (Fluorgard) and a solution associated with chlorhexidine (Duplak). Twenty-four samples from 6 third sound human molars were divided into two groups: 5-min treatment and 10-min treatment. In both the 5-min and 10-min treatment samples, those treated with the chlorhexidine-associated solution showed higher formation of CaF2-like material. In the 10-min treatment group, the samples treated with the neutral solution showed higher formation of CaF2. These results indicated that the products used deposited CaF2 on the enamel surface and may be recommended to aid the prevention and control of dental caries.

The benefits of using fluoride to prevent caries have been known for many years, but a complete understanding of this mechanism is still being researched. The fluoride concentration in the apatitic structure of enamel does not have as significant an effect on reducing caries as a continuous presence of fluoride in the plaque liquid. Concentrated, topical fluoride agents (such as in toothpaste, fluoride mouth rinses, gels, or varnishes) have a different mechanism of fluoride protection than low-concentration applications (such as fluoridated water). In initial caries lesions and plaque, concentrated agents form globules of a calcium fluoride-like material on the enamel surface. This material is fairly insoluble, possibly because it is coated with phosphates or proteins. This mechanism explains how the topical application of a fluoride varnish, two or three times a year, can result in caries reduction.

The possibility of having a commercial product such as waxed floss with an additional agent for controlling and preventing caries is promising. The aim of this research was to determine the uptake of fluoride on tooth enamel in situ after the utilization of a dental floss with fluoride incorporated into the wax. One hundred blocks of bovine enamel were artificially demineralized and randomly separated into a Control Group (C) and a Test Group (T). The dental blocks in group T were mounted two-by-two simulating proximal contacts and were fixed into intra-oral lower arch devices. Eight volunteers with a similar salivary flow and buffer capacity wore devices with the enamel blocks for eight days. During this period of time the subjects applied a 25 cm long portion of a mint waxed floss with fluoride (0.15 mgF/m, Oral-B) between the blocks, 3 times a day for 2 minutes after each meal. At the same time, brushing was carried out with a fluoride-free toothpaste. The alkali-soluble fluoride (CaF2) formed on the enamel was extracted using the Caslavska et al. method and measured with the Orion 96-09 electrode-specific and the EA 720 ion analyzer. The results showed that the group that had the most CaF2 on the enamel (median, minimum and maximum in microF/cm2) was Group T (3.00, 2.11 and 4.00), which differed significantly (p < 0.01) from group C (0.26, 0.10 and 0.69). It was concluded that fluoride uptake on enamel was 11.54 times higher after use of dental floss with fluoride in this study.

Unaesthetic white spot lesions or larger unsightly areas of decalcification around orthodontic brackets remain a significant problem during fixed appliance treatment. This study determined the in vitro fluoride release from 200 fluoride-containing elastomeric ligature ties. With the potentiometric analytic method, the fluoride release was determined in distilled water, for 10 groups of 20 elastomerics, representing the clinical usage in a patient. Readings were taken every 24 hours for 5 days and then every second week for 6 months. The data were analyzed with the Wilcoxon matched pairs signed ranks test. Fluor-I-Ties (Ortho Arch Company Inc., Hoffman Estates, III.) released significant amounts of fluoride compared with the control readings. The fluoride release was characterized by an initial burst of fluoride during the first day and second day, followed by a logarithmic decrease. By the end of the second week 88% of the total fluoride had been leached from the elastomerics, but adequate magnitudes of fluoride were released over the remainder of the test period to aid theoretically in the prevention of demineralization and enhance remineralization of enamel through calcium fluoride and fluorapatite formation. For optimum clinical benefit, Fluor-I-Ties should be replaced monthly. Future prospective longitudinal clinical studies are indicated.

During the caries process complex reactions involving calcium, phosphate, hydrogen and fluoride ions as main species take place. In this study the precipitation and dissolution reactions occurring in suspensions of enamel, hydroxyapatite (HAP) and fluorapatite (FAP) on addition of fluoride were investigated under well-defined conditions. pH and pF were monitored; calcium and phosphate concentrations were measured at selected times; the solid phases were examined by infra-red, X-ray diffraction and transmission electron microscopy. Precipitation of phosphate-containing calcium fluoride crystals, CaF2(P), can cause severe reduction in the calcium ion concentration and release of hydrogen ions from the precipitated phosphate. These reactions result in considerable dissolution of enamel, HAP and even of FAP. More of the added mineral dissolves with 50 mmol/l fluoride than with 10 mmol/l fluoride, mainly due to the greater reduction in calcium ion concentration. This work shows that phosphate-containing calcium fluoride is most likely an important compound to be considered in the caries process.

All currently used topical fluoride agents deposit soluble fluoride as calcium fluoride on enamel or in lesions. Calcium fluoride serves as a source of fluoride for the formation of fluorapatite. The latter phase is formed when pH drops in plaque, not during topical application. The potential for calcium fluoride formation should probably be increased in topical fluoride agents. In countries with low caries prevalence, the clinical recommendations for topical fluoride need to be reconsidered. Toothpaste is the basic fluoride regimen recommended for everybody. The need for additional fluoride supplementation depends on caries activity. There is no distinct difference in the caries-preventive effects of concentrated fluoride solutions, gels, or varnishes. Thus, the choice of method depends on costs, convenience, patient acceptance, and safety. The use of fluoride varnishes has proven to be a feasible and safe method of fluoride application. With fluoride varnishes, the amounts of fluoride exposure can be better controlled, and less chair-time is required compared with conventional solutions and gels. No dose-response effect to concentrated fluoride agents is apparent, and the benefit of frequent application is not clearly established. In individuals with the most severe cariogenic challenge, combinations of fluoride and antimicrobials may give better clinical effects than fluoride alone.

As calcium fluoride formation following topical application of fluoride may be responsible for at least some of the caries-reducing effect of fluoride, the concentration of fluoride necessary to induce its formation were examined. The aim was to determine the degree of supersaturation with respect to calcium fluoride necessary for inducing its spontaneous precipitation, with close reference to its possible formation and retention on dental hard tissue when topical fluoride solutions are used clinically. Powdered enamel or brushite were suspended for 4 h in aqueous solutions buffered at pH 7.2 and 5.0. After the equilibration, ion concentrations were determined and degrees of saturation with respect to apatite and brushite were calculated. In aqueous solutions at pH 7.2 and 5.0 with similar concentrations as those found in the equilibrated suspensions the fluoride concentration was adjusted to from 5 to 500 parts/10(6). After 2 h of gentle agitation the supernatant was analysed, the precipitate (if any) isolated and examined by X-ray diffraction. Initiation of spontaneous calcium fluoride formation required a calcium fluoride ion-activity product of 10(-7.6) or more, 300 parts/10(6) fluoride were necessary to initiate calcium fluoride formation in neutral solution saturated with enamel, and the increased solubility of enamel apatite at low pH allowed calcium fluoride formation from solutions with as low as 100 parts/10(6) fluoride. When phosphate was present in the solution a competing apatite formation could mask the calcium fluoride formation. In neutral solutions saturated with respect to brushite, spontaneous fluorapatite formation was initiated by 100 pats/10(6) fluoride. With 200 parts/10(6) fluoride a further competing formation of calcium fluoride occurred.

Raman spectra containing the distinct band at 322 cm-1 due to CaF2 or CaF2-like material formed in/on fluoridated bovine enamel were recorded using a micro-Raman spectrograph. Due to increasing levels of background fluorescence with increasing thickness of enamel, the Raman measurements were carried out on thin regions of wedged enamel sections. The distribution of the CaF2 or CaF2-like material was estimated using a simple model. The results indicate that 1/3 of the total CaF2 was concentrated within the narrow depth < 2 microns with high CaF2 concentrations (> 10 wt%), and that the majority of the CaF2 was distributed over the depths up to 26 microns (1 wt% CaF2). SEM observations on fractured fluoridated enamel confirmed that morphological changes were present in the depth range comparable to that of the high CaF2 concentration region expected from the Raman analysis. In deeper regions where lower concentration (< 10%) but a large amount of CaF2 was still expected, the SEM images failed to distinguish between the normal and fluoridated enamel. After KOH treatment, the Raman spectra did not show evidence of the CaF2 peak and the SEM micrographs also confirmed the removal of globules. The peak position of the Raman band of the CaF2 formed by the fluoridation was identical to that of pure CaF2. However, the linewidth was 23 cm-1 (FWHM) and a factor of 2 broader than that of pure CaF2 (12 cm-1). This implies that the lattice dynamics of the CaF2 formed by fluoridation is different from of pure CaF2, and that the material formed is 'CaF2-like' or 'disordered CaF2'.

The formation of CaF2 was measured on sound enamel and in artificial, standardized (acidified gelatin, pH 4.5) caries-like enamel lesions after exposure to: (a) dentifrice/saliva slurries adjusted to relevant F-concentrations of approximately 100 or 8 ppm by appropriate addition of 1,000 ppm F NaF or Na monofluorophosphate (MFP) dentifrice, respectively, or (b) a mixture of saliva with a 0.2% NaF solution obtained by a usual 1-min rinse procedure or an aqueous solution of 0.2% NaF. CaF2 was determined after extraction with KOH and fluoride analysis by gas chromatography. Only negligible amounts of CaF2 were produced on sound enamel ranging from (mean +/- SEM) 0.76 +/- 0.14 micrograms F/cm2 with the 0.2% NaF solution to as little as 0.04 +/- 0.06 with the MFP dentifrice slurry. In caries-like enamel lesions, the CaF2 production with the 0.2% NaF solution/saliva mixture corresponded to 3.7 +/- 0.4 micrograms F/cm2 and corresponding amounts obtained with the dentifrice/saliva slurries were 1.5 +/- 0.19 micrograms F/cm2 with NaF, but only 0.19 +/- 0.04 with MFP. It was suggested that the deposition of CaF2 in the micropores of early lesions can be expected to be an important mechanism with F rinses, probably to some extent with NaF dentifrices, but barely with MFP dentifrices. The formation of CaF2 on sound enamel is unlikely to play a significant role in the caries-reducing effect of F rinses and F dentifrices.

Fluoride uptake on and in enamel during topical application of acidulated solutions was studied. The variables were different time intervals and different pH levels of the treatment solutions. The experiment was carried out with human enamel exposed to 2% NaF solutions, pH 3.5 and 5.5, for 30 sec, 60 sec, 5 min, and 60 min. The amounts of fluoride formed on (as calcium fluoride) and in (as fluorapatite) enamel were determined by chemical assessments, and scanning electron microscopy provided the visualization of the deposits on the surface. It could be demonstrated that the two pH levels caused deposition of large amounts of calcium fluoride and that almost twice as much was deposited at pH 3.5 as at 5.5. The amount of deposit increased rapidly with time of exposure in both situations compared with similar experiments with neutral fluoride solutions. Firmly bound fluoride was incorporated in the enamel only during the 60-min incubation.

The precipitation of Ca-compounds in ageing dental plaque leads to the formation of calculus. Bacterial lipoteichoic acid (LTA) has been discussed as Ca-carrier in this process (Zoon et al., 1989). Therefore in this study, LTA was isolated from oral streptococci and tested for its influence on the precipitation of Ca-phosphate. LTA-containing bacteria, LTA-free bacteria and isolated LTA were added to the reaction mixtures for Ca-phosphate precipitation and the amount of precipitated mineral was measured. LTA-containing cells and, above all, LTA, inhibited Ca-phosphate precipitation in a distinct pH-range just above the acid solubility of the mineral by complexing Ca(2+)-ions. Experiments with Ca-fluoride in place of Ca-phosphate showed that LTA did not affect the precipitation of this mineral.

Deposition of alkali-soluble fluoride on enamel in the presence and absence of an acquired pellicle was studied in vitro during a single topical application of a 2% sodium fluoride solution at neutral pH. Five experimental groups of repeated measures design were established. The amount of alkali-soluble fluoride formed on enamel (i.e., calcium fluoride) was measured by chemical assessments and by SEM. The results showed that there were no differences among the groups demonstrating the incapacity of pellicle to interfere with deposition of alkali-soluble fluoride on enamel. The fluoride ions are thus able to reach the enamel in spite of the presence of the pellicle.

The formation of calcium fluoride (CaF2) was measured on sound enamel (SE) and in caries-like enamel lesions (CL) after treatment in vitro with 2% neutral NaF or Duraphat. The caries-like lesions were created by exposure to acidified gel at pH 4.5 within a 0.07-cm2 window punched in water-repellant tape. The same window area was used in series (n = 10) of SE or CL during the application of NaF for 1 or 5 min or for 18 h or Duraphat for 6 or 18 h. CaF2 was extracted with 1 M KOH for 24 h, and fluoride was determined by gas chromatography. The short-term applications of NaF produced only negligible amounts of CaF2 on SE. The amounts of CaF2 in CL after 5 min application of NaF corresponded to (mean +/- SEM) 27 +/- 2.0 micrograms F/cm2. More than half of this amount was observed after only 1 min exposure to the NaF solution. The quantities of CaF2 in CL were similar after 6 and 18 h application of Duraphat, amounting to 26 +/- 2.2 and 31 +/- 2.2 micrograms F/cm2, respectively, suggesting that the reaction was essentially terminated after 6 h. These amounts were only about one fourth of the quantity obtained after 18 h exposure to the NaF solution. Thus, the conventional 5-min treatment with NaF produced the same amount of CaF2 in CL as 6 or 18 h exposure to Duraphat.

This paper discusses loosely bound fluoride and its role in dental caries and prevention. Loosely bound fluoride (abbr. by Fa) is fluoride adsorbed onto enamel mineral crystallites. Several recent studies indicate that a high total level of fluoride in enamel does not guarantee protection against caries. This leads to the conclusion that a major part of fluoride present in the solid enamel is not active in prevention. The adsorption of Fa to the mineral under acidic conditions is described. Most likely there is a dynamic equilibrium between fluoride in solution and adsorbed Fa at the crystal surface interface. When the crystallite is completely covered by adsorbed Fa, there is a maximum inhibition of dissolution. The rate of dissolution of mineral depends on pH, the actual concentrations of calcium and phosphate in the liquid in contact with the crystallites, and on the fraction of the surface covered by adsorbed fluoride. The fluoride, Fs, localized in the inner part of the crystallites is relatively unimportant. "CaF2-like" material can be formed on and in enamel depending on conditions. The in vivo-formed globular "CaF2-like" material is not pure CaF2 and releases F- ions when dissolving; these ions will also be partly adsorbed as Fa in and on enamel. Presently, the amount and importance of Fa originating from in vivo-formed "CaF2-like" material are not known. The level of fluoride, Fa, necessary for strong inhibition of enamel demineralization in vitro is estimated to correspond to a fluoride concentration, FL, in the liquid phase of 1 ppm or 50 mumol/L fluoride ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Liberation of stannous fluoride incorporated in the alloy powder before amalgamation was demonstrated for all the amalgams tested in this study. This liberation was observed for stannous fluoride concentrations of 0.5% and 1%. Clear differences were noted in relation to the type of amalgam studied. Through the use of a non destructive method (activation with charged particles) it was possible to measure the fluoride concentration in enamel before and after the contact with the fluoridated amalgam. This analysis demonstrated that the fluoride liberated from the amalgam was trapped by enamel in contact with alloys containing 0.5% or 1% of stannous fluoride. The enrichment in fluoride was very important in the first weeks and remained high after four months. No significant difference appeared between alloys fluoridated at 0.5% and 1%. The dissolution of calcium fluoride through a KOH treatment showed that the amount of stable fluoride (fluorapatite) formed was important.

The amount of alkali-soluble and alkali-insoluble fluoride was determined in human enamel after one- and six-hour treatments with Duraphat. The application was carried out on: (1) slightly demineralized enamel covered with artificial plaque, (2) cleaned, slightly demineralized enamel, and (3) sound enamel without pre-treatment. After a single Duraphat treatment lasting six hours, fluoride uptake was higher than after Duraphat treatment for just one hour in all experimental groups. More fluoride was acquired in both slightly demineralized, plaque-covered and slightly demineralized, cleaned enamel than in sound enamel. Plaque significantly hampered the formation of alkali-soluble fluoride precipitation on demineralized enamel, but its influence on the amount of fluoride taken up by the enamel was minor.

The structural changes in human enamel during exposure to an acetate buffer, pH 4, containing 150 parts/10(6) fluoride have been studied using scanning electron microscopy and polarized light microscopy. After exposure for 2 h the enamel surface was covered by a fine-granular layer of calcium fluoride. The underlying enamel was highly eroded with an increased pore volume in the outer layer. Following an equilibration period of 3 months the uptake of fluoride in the apatite lattice had resulted in a highly mineralized, 100-micrometer-thick surface layer rich in fluoride covering a subsurface porous zone with an unchanged fluoride content. The deeply located, caries-like porous zone may have provided calcium and phosphate for saturation of the liquid.

Polished enamel blocks with known surface areas were obtained from human mandibular incisors. Acidulated phosphate fluoride was applied for 4 min and washed off after additional contact times of 0, 2, 6 and 24 h, respectively. The enamel fluoride concentrations were determined in three successive etch depths before and after extraction in 1 M KOH for 24 h. The predominant reaction product was CaF2. The concentration of the fluoride bound as fluorapatite or fluorhydroxyapatite reached an optimal level after a 6-h contact time.

Various amounts of enamel-apatite powder were suspended in an acetate buffer (pH 4.5) containing sufficient fluoride to give molar ratios of fluoride/apatite from zero to unity. The suspensions were equilibrated at 20 degrees C for periods between 4h and 1 year, with continuous gentle stirring. Solubility studies showed dissolution of hydroxyapatite, formation and re-dissolution of calcium fluoride and formation of fluorapatite. The amount of mineral dissolved was low during the fluorapatite formation and increased by a factor of approx. 10 as equilibrium was approached. The fluoride content of the solid apatite, which ranged from 0.1 to 70 mol% fluorapatite, only influenced the solubility slightly, whereas the fluoride content of the bathing solution had a large effect. X-ray diffraction showed a linear correlation between the fluoride content and the a-axis of the apatite.

The solubility of various Ca(II) salts, hydroxyapatite, and powdered human dental enamel in the presence of simple carbohydrates was studied by determining the complex strength between Ca(II) and the carbohydrates. In 1.0 M CaSO4, the following simplified sequence of complex strengths was obtained for the more common carbohydrates: Na-citrate greater than D-sorbitol greater than xylitol greater than D-mannitol greater than D-fructose greater than D-glucose greater than D-xylose. Whereas the more soluble Ca(II) compounds (like CaSO4) exerted measurable complexation with xylitol, no such complexation was found with hydroxyapatite and enamel powder. This also concerned other alditols. Calculation of the stability constants (K) showed sorbitol (K = 0.81 M) and xylitol (K = 0.67 M) to form stronger complexes in saturated CaSO4 than other alditols. The most suitable coordination site appeared to be a vicinal cis-cis-triol. Precipitation studies showed that 0.5 M xylitol and 0.5 M sorbitol significantly retarded the formation of calcium phosphate precipitates from a solution of Ca(II) and phosphate, compared with the effect caused by glucose, sorbose, or xylose. The effect caused by xylitol and sorbitol was explained in terms of partial displacement of water molecules in the primary hydration layer of Ca(II) ions, caused by competition between polyol and water molecules. In the presence of aldoses and ketoses, virtually instantaneous precipitation occurred. These results suggest that open-chain alditols may influence the chemical reactions of Ca(II) in plaque, saliva, and caries lesions. Alditols do not function as demineralizing agents of the teeth, however. Through the retarding effect on calcium phosphate precipitation, alditols may favorably govern remineralization of carious lesions.

After single, oral doses, 8 h profiles of fluoride (F) concentrations in plasma were determined in healthy human volunteers. Bioavailability of F from bone-meal, calcium and CaF2 tablets was evaluated in relation to that of NaF. Tablets were administered either whole or as a finely-ground powder, either to fasting subjects or with breakfast. Availability was lowest from whole tablets taken by fasting subjects, and highest from powdered substances given with breakfast. Mean F availabilities ranged between 7.2 and 39 per cent with bone-meal tablets, between 20 and 59 per cent with Ca tablets, and between 0 and 47 per cent with CaF2 tablets.

The dissolution rate of CaF2 tablets in vitro and the degree of F absorption in vivo after tablet intake in man were investigated. 50% of total F was released in 0.1 N HCl after 45 min whereas virtually no release was seen in H2O or in 0.2 M PO4-buffer pH 6.8. In spite of the modest release of F in simulated gastric juice in vitro no F absorption as judged from the plasma fluoride concentration curve was seen within 6 h after intake of 4 mg F as CaF2 tablets.

The retention of alkali soluble (CaF2) and alkali insoluble (fluorapatite) fluoride in sound enamel and demineralized enamel 2 wk after application of Duraphat was investigated in a group of orthodontic patients from whom pairs of homolog premolars were to be extracted. Demineralization of the enamel was induced during a 4-wk period prior to application of fluoride by applying orthodontic bands to the premolars. The bands also remained attached to the teeth during and after application of fluoride (2 wk) to maintain a cariogenic environment. Three consecutive enamel layers (approximately 5 microns) were subsequently etched off. A significant uptake of fluoride in the first and second layer of sound enamel and in all the three enamel layers of demineralized enamel was found. More fluoride was found in demineralized enamel and a higher proportion of this fluoride was found to be in an alkali insoluble form compared with the fluoride in sound enamel. The SEM study showed a rough enamel surface after three consecutive acid etchings. The etching pattern differed within the etched area. It was suggested that the variation in etching pattern might be due to differences in orientation of the crystallites and the original surface morphology.

Clinical experiments were performed to investigate the effect of fluoride on carious lesion development and on lesions established during fixed orthodontic therapy. All presently available fluoride agents are developed from the concept of fluoridating the enamel in the form of fluorhydroxyapatite. Recent research has indicated, however, that calcium fluoride formation may be a major aspect of the mechanism of the cariostatic effect of topical fluoride. Therefore a fluoride solution with very low pH (1.9) that induced large amounts of calcium fluoride also was tested on lesion development underneath orthodontic bands. Daily fluoride mouth rinsing with a 0.2% solution sodium fluoride (NaF) retarded lesion development significantly, whereas the fluoride solution with low pH inhibited lesion formation completely. Fluoride applied as a mouth rinse to plaque-covered lesions underneath orthodontic bands retarded lesion progression. The remineralizing capacity of saliva was found to be rapid in the absence of any fluoride. Although white spot lesions may remineralize and even disappear, most of the emphasis should be directed against prevention of carious lesion development during treatment with fixed orthodontic appliances.

Demineralization of enamel was induced by applying orthodontic bands in 15 patients having two of their premolars extracted for orthodontic reasons. After a 4-wk caries induction period, eight patients were instructed to rinse their teeth once daily with a neutral 0.05% NaF solution, whereas seven patients received a single treatment with a neutral 2% NaF solution. The bands were reattached to the teeth during the fluoride treatment period and the teeth were extracted after two more weeks. Three consecutive enamel layers were etched off, and a significant uptake of fluoride in all three layers were found in both treatment groups. A larger part of the deposited fluoride was retained in an alkali insoluble form (i.e. fluorapatite) compared with previous studies of sound enamel. It is suggested that the chemical conditions in the cariogenic milieu were favorable for transformation of the fluoride into a stable apatite structure.

In order to quantitatively examine fluoride uptake by bone and the effect on its chemical and physical properties, rat bone was incubated in acidic buffer solutions (pH 5) with fluoride concentrations of 0-1000 ppm F. After 1 wk incubation, there was a substantial increase in the crystallinity of the bone mineral with increasing fluoride concentration in the solution. The calcium concentration in the solutions used for incubation decreased dramatically, with increased levels of fluoride in the solution, approaching a plateau. The phosphate concentration initially decreased, with increasing levels of fluoride in proportion to the decrease of calcium concentration, and then increased when the fluoride concentration of the solution was above 200-300 ppm. These phenomena, when considered with X-ray diffraction data, reflected the formation of CaF2. The increase of the phosphate concentration in the solution suggests that the presence of excessive fluoride in the acidic buffer solution may promote the dissolution of soluble bone apatites, in spite of the dissolution-preventive activity of fluoride.

There are indications that sodium lauryl sulfate may reduce the cariostatic effect of fluoride when present together with sodium monofluorophosphate during topical application. The aim of the present study was to examine the in vitro deposition of alkali soluble fluoride on enamel during topical application with sodium fluoride in combination with sodium lauryl sulfate. It was found that increasing amounts of lauryl sulfate decreased the amount of alkali soluble fluoride deposited on the enamel. The amount of fluoride deposited from toothpaste supernatants was less than that from aqueous solutions of NaF with the same concentration of fluoride. Enamel pieces, pretreated with sodium lauryl sulfate showed a reduced deposition of alkali-soluble fluoride after incubation in a fluoride solution. It was also observed that the presence of lauryl sulfate increased the solubility of CaF2 in water.