Alkali-soluble Fluoride Research Articles

Impact of Calcium Lactate Pretreatment on Enamel Fluoride Uptake: A Comparative In Vitro Study of Different Fluoride Types and Concentrations.

(1) Background: This study aimed to establish the effect of calcium lactate enamel pretreatment related to different fluoride types and concentrations on the enamel uptake of alkali-soluble fluorides. (2) Materials: In a blind and randomized in vitro study, a total of 60 teeth are used. The first 30 teeth were cut and randomly allocated into one of the following treatments: (A) calcium lactate pretreatment followed by three different fluoride solutions; (B) the "Fluoride only" group, with slabs treated with three different fluoride solutions; (C) the "Calcium only" group, with slabs treated with calcium lactate solution; (D) slabs treated with deionized water (negative control group). The next 30 teeth underwent all the above described group procedures but were treated with lower fluoride concentrations. Fluoride was extracted from enamel using 1 M KOH solution and analyzed using a fluoride ion-specific electrode. (3) Results: The findings revealed that slabs treated with NaF following calcium lactate pretreatment exhibited significantly greater enamel uptake of alkali-soluble fluoride compared to other substrates. This significant effect was not observed at lower fluoride concentrations. (4) Conclusion: The study demonstrates that pretreatment with calcium lactate followed by treatment with NaF at 226 ppm F significantly enhances the uptake of alkali-soluble fluoride in enamel compared to other fluoride types.

Calcium pretreatment enhances fluoride reactivity with enamel and dentine

ObjectiveHigh fluoride concentration treatments are known to react with enamel and dentine forming calcium fluoride (CaF2)-like deposits, but strategies to improve this reactivity beyond increasing fluoride concentration/reducing pH in fluoride treatments have not been explored. Here we investigated the ability of a calcium pre-treatment to improve fluoride reactivity. DesignIn a blind and randomized in vitro study, sound and carious enamel and dentine slabs (n = 11/group) were randomly allocated into one of the following treatments: Deionized water (negative control); 0.05% sodium fluoride (F, positive control); 150 mM calcium lactate solution followed by 0.05% sodium fluoride solution (Ca→F); 150 mM calcium lactate solution premixed with 0.05% sodium fluoride solution (CaF2, active control). Alkali-soluble fluoride (representing CaF2-like deposits formed on the substrates) was extracted from the slabs using 1 M KOH for 24 h and measured by an ion-specific electrode. Carious slabs were further observed under scanning electron microscopy (SEM). Data were analyzed by two-way ANOVA followed by Tukey test. ResultsThe Ca→F treatment enhanced fluoride reactivity with all tested substrates when compared with F alone. Carious substrates had a greater reactivity with F and Ca→F than their respective sound substrates, confirming that increased porosity enhances the reactivity with fluoride. Alkali-soluble fluoride concentration after the CaF2 treatment did not differ among the different substrates, suggesting this treatment causes only contamination with preformed CaF2, which was noted under SEM. ConclusionA calcium pretreatment enhances the reactivity of fluoride with enamel and dentine.

Enhancing the Anti-Erosive Properties of Fluoride and Stannous with the Polymer Carbopol

This in vitro study investigated whether Carbopol 980 polymer could potentiate the anti-erosive effect of solutions containing sodium fluoride (F) and sodium fluoride associated with stannous chloride (FS). The dissolution of hydroxyapatite treated with the experimental solutions (F [500 ppm F^–], F + Carbopol [0.1%], FS [500 ppm F^– + 800 ppm Sn²⁺], FS + Carbopol) was evaluated. Deionized water was the negative control, and a commercial mouth rinse (AmF/NaF/SnCl₂; 500 ppm F + 800 ppm Sn²⁺; Elmex® Erosion Protection) was the positive control. The solutions were also evaluated in an erosion-rehardening protocol, with two treatments per day, using bovine enamel specimens (n = 15) and human saliva. The acid challenge was performed using 0.3% citric acid (pH 2.6) for 2 min. Microhardness was measured at different times: baseline, after the first erosive challenge, after treatment, and after the second erosive challenge. Based on microhardness values, the demineralization, rehardening, and protective potentials were calculated. The alkali-soluble fluoride on enamel surfaces was also measured. Data were analyzed using ANOVA and Tukey tests (α = 0.05). Groups treated with FS + Carbopol showed the lowest hydroxyapatite dissolution and the highest rehardening and protective potentials. The measurement of alkali-soluble fluoride on enamel surfaces was also higher in the FS + Carbopol group. Carbopol was able to significantly increase the protective effect of the fluoridated solutions in addition to optimizing the adsorption of fluoride on the enamel surface.

The Effect of Salivary Calcium and Fluoride Toothpaste on the Formation of KOH-Soluble Fluoride: In Vitro Study.

The aim of this in vitro preliminary study was to assess the effect of smokers' saliva (assuming their higher calcium concentration) in combination with fluoridated toothpaste on the enamel uptake of alkali-soluble (KOH-soluble) fluoride. Four enamel slabs were cut from each of 14 impacted third molars and randomly assigned into 4 groups. Unstimulated saliva samples were collected from two age and sex matched volunteers. One of the samples was taken from a heavy smoker and the other sample was taken from a non-smoker. Two groups (A and B) were shaken in saliva (A in smoker's saliva, B in nonsmoker's saliva) for 5 min and then shaken for 3 min in a toothpaste/deionized water slurry (1:3 w/w). One of the groups (group C) received no saliva treatment and was only shaken in toothpaste slurry for 3 min. The treatment was repeated after a 6-hour period. One of the groups (D) served as a control group with no treatment. Calcium concentration in the smoker's saliva was higher than in the nonsmoker's saliva. The enamel uptake of KOH-soluble fluoride in group A was significantly higher than that in the other two treatment groups, B and C. The enamel uptake of KOH-soluble fluoride in all 3 groups was statistically different from that in the control group. These results demonstrate that saliva collected from a heavy smoker, which had higher salivary calcium concentration, enhances enamel uptake of alkali-soluble fluoride and encourages us to conduct a large-scale study.

Mechanisms of action of fluoridated acidic liquid dentifrices against dental caries

ObjectiveThis study attempted to clarify the mechanisms of action of fluoridated acidic liquid dentifrices against dental caries. DesignIn the in vitro leg, enamel specimens were submitted to a pH-cycling model, treated with distinct dentifrices (0, 550μgF/g pH 4.5 and pH 7.0, 1100 or 5000μgF/g pH 7.0) and analyzed using hardness. Alkali-soluble fluoride (F) deposition was quantified on pre-demineralized specimens treated with the dentifrices. In the clinical leg, 2-to-4-year-old children who had been using liquid dentifrices for 6 months (550μgF/g pH 4.5 or pH 7.0 or 1100μgF/g pH 7.0) had their plaque samples collected 5 and 60min after the last brushing. Fluoride uptake in whole plaque was evaluated. ResultsThe reduction of the pH had a partial preventive effect on subsurface hardness loss only. [F] had a significant influence on the deposition of fluoride, surface and subsurface hardness loss. In vivo, the reduction of the pH was able to significantly increase plaque F uptake, leading to similar levels as those found for the neutral dentifrice containing twice [F]. ConclusionThe results obtained from in vitro studies whose design does not include the presence of dental plaque should be interpreted with caution.

Alkali-soluble fluoride deposition on enamel after professional application of topical fluoride in vitro

Since the efficacy of topical fluoride products is related to the fluoride (F) availability and its reactivity with enamel, this study was conducted. The F concentration of the following materials was verified: I- acidulated phosphate fluoride (APF) gel (1.23% F), II- APF foam (1.23% F) and III- Varnish (2.26% F). Forty blocks of bovine enamel were divided into 4 groups and treated according to the materials described, being one of them used as control. Loosely bound fluoride (''CaF2'') was determined on enamel after extraction with 1.0M KOH and analyzed by ion-selective electrode. Total F concentration found in gel was 12,642, in foam 12,755 and in varnish 23,183 mg F/g. All products formed statistically higher amounts of ''CaF2'' on enamel compared to the control group (p < 0.05), but the difference between them was not significant (p > 0.05). Thus, ''CaF2'' formation was not proportional to the total F content in the products, suggesting that the pH and the vehicle used are more important.

Alkali-soluble fluoride deposition on human enamel exposed to monofluorophosphate-containing toothpastes in vitro.

Enamel specimens from unerupted third molars were treated with the supernatant of monofluorophosphate (MFP)-containing toothpaste slurries in water. Calcium fluoride-like particles were formed on the enamel surface during a 24-h exposure. The globules were soluble in alkali. More particles were seen on enamel treated with a toothpaste containing both MFP and NaF. The experiments showed that the calcium fluoride-like material formed on enamel after treatment with MFP-containing toothpaste probably originates from the free fluoride present in the pastes. The relatively moderate deposition of fluoride may be of clinical significance because the teeth are so frequently exposed to toothpaste. No firmly bound fluoride was found on treatment of enamel with MFP-containing toothpaste.

Fluoride acquisition on and in fluorotic human enamel after topical application in vitro

The uptake of alkali soluble and alkali insoluble fluoride on and in fluorotic enamel was investigated in vitro. Teeth from Kenya, assigned score 3 in accordance with Thylstrup-Fejerskov's fluorosis index, were used. The enamel was treated with either a neutral 2% NaF solution, a 0.2% NaF solution (pH 5.5), or the supernatant from a 0.1% NaF-containing toothpaste (pH 7). The treatment time was 1 h. The reaction product formed on the enamel was analyzed by KOH extraction and acid etching. Significantly higher amounts of alkali soluble fluoride were formed on the enamel from the 2% and 0.2% NaF solutions, as compared with the control. There was also a significant increase in the firmly bound fluoride after treatment with the neutral 2% NaF solution.

Uptake of KOH-soluble and KOH-insoluble fluoride in sound human enamel after topical application of a fluoride varnish (Duraphat) or a neutral 2% NaF solution in vitro.

The uptake of alkali-soluble fluoride (calcium fluoride-like material and adsorbed fluoride) and alkali-insoluble fluoride (apatitically bound fluoride) on sound human enamel from treatment with Duraphat or a neutral 2% NaF solution was investigated in vitro. Blocks from impacted third molars were used. More fluoride was deposited on the enamel from the neutral 2% NaF solution than from the Duraphat treatment. All the fluoride could be dissolved in alkali. Globules of calcium fluoride-like material were demonstrated by scanning electron microscopy. Chemical analysis showed no measurable increase in the apatitically bound fluoride (alkali-insoluble fluoride) after brief exposures. Duraphat-treated samples submerged in water after the exposure lost only about 50% of the deposited fluoride, whereas samples treated with 2% NaF are known to lose all their fluoride under similar circumstances, a condition which may be related to the favorable clinical effect of Duraphat.

Acquisition of alkali-soluble fluoride by enamel through treatment with NaF-containing toothpastes in vitro.

The first aim of the present study was to examine if alkali-soluble fluoride (calcium fluoride-like material and adsorbed fluoride) forms when a NaF-containing toothpaste is applied on human enamel surface in vitro. The centrifuged supernatants of toothpastes dissolved in distilled water were used and four different commercial NaF-containing toothpastes were tested. The second aim was to investigate if pyrophosphate would interfere with the deposition of alkali soluble fluoride. The formation of alkali-soluble fluoride was determined by chemical analysis and visualized by scanning electron microscopy (SEM). It was ascertained that all tested toothpastes contained free fluoride according to the manufacturers' specifications. It was shown that they promoted deposition of alkali soluble fluoride on the enamel surface. The amount of deposited material increased with the time of exposure. The clinical effect of a NaF-containing toothpaste may thus well depend on an initial formation of alkali-soluble fluoride. Fluoride from this reservoir may adsorb onto the enamel crystals and inhibit further demineralization or increase the rate of remineralization during cariogenic challenges. It was also demonstrated that pyrophosphate did not interfere with the deposition of alkali soluble fluoride.

Deposition of alkali‐soluble fluoride on enamel surface with or without pellicle

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.

Formation of fluoride on enamel in vitro after exposure to fluoridated mouthrinses

The aim of this study was to quantify the formation of alkali-soluble fluoride (loosely bound fluoride such as calcium fluoride-like material and absorbed fluoride) and alkali-insoluble fluoride (firmly bound fluoride or apatitically bound fluoride) when fluoride mouthrinsing solutions were applied on sound human enamel in vitro. Two commercial products containing 0.2% or 0.05% NaF were used during 30 sec, 60 sec, 5 min, and 60 min. The formation of loosely bound fluoride was determined by KOH extraction and visualized by scanning electron microscopy. The firmly bound fluoride was measured by three consecutive acid etchings of the enamel. Even during short periods of application there were deposits on the enamel surface. The amount of deposit increased with time of exposure to the 0.2% NaF solution. Only after treatment for 60 min with 0.05% NaF were significant amounts of alkali-soluble fluoride deposited. No measurable amounts of firmly bound fluoride were observed.

各種フッ化物応用後の健全エナメル質におけるアルカリ溶解性フッ素濃度

各種フッ化物応用後の健全エナメル質におけるアルカリ溶解性フッ素濃度

Fluoride acquisition on and in human enamel during topical application in vitro.

Fluoride acquisition during topical fluoride treatment was studied after different time intervals, at different concentrations and at different pH. The effects of pretreating the enamel with Ca++, and of pre-etching were also tested. Four experimental groups of repeated measures design were established. Chemical assessments were made of the amounts of fluoride formed on (as alkali soluble fluoride, i.e., calcium fluoride) and in enamel (as firmly bound fluoride). The depositions on enamel were also demonstrated by SEM. The amounts of alkali soluble fluoride on enamel increased with time, concentration, pH-decrease and calcium availability. The time of exposure seemed to be the major factor. The amounts of fluoride deposited on enamel outranged by far (greater than 70%) the amounts of fluoride acquired in the enamel. The formation of alkali soluble fluoride on enamel is probably limited by the availability of calcium ions. It is suggested that the fluoride on enamel may protect the enamel surface and serve as a reservoir of fluoride.

Effect of sodium lauryl sulfate on the deposition of alkali-soluble fluoride on enamel in vitro.

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.

The influence of plaque on reaction mechanism of MFP and NaF in vivo.

A modified Intra-oral Cariogenicity Test was used to study the influence of plaque on the reaction mechanism of sodium monofluorophosphate (MFP) or sodium fluoride (NaF) in either sound or demineralized enamel in vivo. Volunteer students, wearing mouth appliances holding enamel blocks, rinsed their mouths with MFP or NaF solution (1,000 ppm F-) three times a day. The amount of loosely-bound and acquired fluoride was determined after an experimental period of five days in plaque-covered, demineralized (PCD); clean, demineralized (CD); plaque-covered, sound (PCS); and clean sound enamel (CS). While no measurable loosely-bound fluoride could be found after MFP treatment, NaF caused deposition of a significant amount of alkali-soluble fluoride in all experimental groups. After MFP rinses, fluoride concentration in the enamel was increased in the following order: CS, PCS, CD, and PCD. After NaF treatment, demineralized enamel exhibited a higher fluoride acquisition when compared with sound enamel. Plaque had a minor effect on F- acquisition. It is concluded that demineralization of enamel enhances F- uptake from both NaF and MFP solutions. In the presence of plaque, F- acquisition was additionally increased only after MFP rinses in vivo.

フッ化チタンアンモニウム溶液によるエナメル質の耐酸性について

The purpose of this study was to investigate the contribution of fluoride and titanium uptake in powdered enamel to the acquisition of acid resistance.Experiments were made in vitro by treatment with solution of (NH4) 2 TiF6 (9000 ppm of F, pH 3.4) or APF (acidulated phosphate fluoride solution) for 3 minutes at 37°C with powdered enamel (particle size 70-140 μm), and 24-hour washing with synthetic saliva or 1M KOH solution was used to distinguish the soluble and permanently bound fluoride. Chemical analyses were performed to determine fluoride, titanium, calcium, and phosphorus. Acid solubility of enamel was evaluated to determine the calcium released from powdered enamel into acetate buffer (pH 4.5). The reaction products were identified by X-ray diffractometry.A large amount of fluoride uptake, most of it in the form of CaF2, was found after application of APF. Synthetic saliva or KOH washing removed most of the fluoride from APF treated enamel, but (NH4) 2 TiF 6-treated enamel had lower levels of fluoride uptake and higher retention after both washings. These facts indicated that a higher level of more permanently bound fluoride formed in (NH4) 2 TiF6-treated enamel.Titanium in (NH4) 2 TiF6-treated enamel was resistant to synthetic saliva washing, but the KOH wash caused a partial release of titanium.The acid solubility test of fluoride-treated enamel showed the same degree of acid resistance before and after synthetic saliva wash. However, the KOH wash decreased an acid resistance of both types of fluoride-treated enamel. A decrease of acid resistance in APF-treated enamel may contribute to the release of alkali-soluble fluoride such as CaF2. In the case of (NH4) 2 TiF6, a decrease of acid resistance might be related to the titanium concentration in enamel. The release of fluoride and titanium from (NH4) 2 TiF6-treated enamel into 1MKOH solution suggests a hydrolysis of titaniumfluoride compound, which forms an organometallic bond with the enamel protein called“glaze”, rather than a release of CaF2.As the results, it is suggested that glaze-like substance is soluble in strong alkali such as 1MKOH soluion but stable in acid circumstances, and controls acquisition of acid resistance of powdered enamel.

Fluoride retention in clean and plaque-covered demineralized enamel in vivo after application of monofluorophosphate.

The retention of fluoride in clean and plaque-covered demineralized enamel in vivo was measured 1 wk after a single application of a MFP solution with low or high content of free fluoride. Demineralization of the enamel was induced in vivo during a 4-wk period prior to application of fluoride by applying orthodontic bands on a pair of premolars scheduled for extraction of orthodontic reasons. The band from one tooth of each pair was then removed and the tooth cleaned (clean enamel lesion). The band on the contralateral tooth (plaque-covered enamel lesion) was left in place. The MFP solutions were applied and the teeth extracted after one more week. The chemical form of fluorine in the lesions was analyzed by conventional acid etching of the enamel combined with KOH dissolution and by a nondestructive surface analysis using ESCA to detect intact monofluorophosphate ions. The ESCA measurements showed that MFP was only present in the clean enamel lesions, indicating complete hydrolysis by dental plaque. Alkali soluble fluoride could be extracted from both plaque-covered and clean enamel lesions. Conflicting results regarding the amount of fluoride uptake in the lesions were obtained with the acid etching and the ESCA technique. It was thus not clearly established whether plaque enhanced fluoride uptake in carious lesions after MFP application.

Fluoride uptake in plaque-covered enamel after treatment with the fluoride lacquer Duraphat.

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.

Uptake and retention of alkali-soluble and alkali-insoluble fluoride in sound enamel in vivo after mouthrinses with 0.05% or 0.2% NaF.

The uptake and retention of alkali-soluble and alkali-insoluble (fluorapatite) fluoride in human teeth in vivo was investigated in a group of orthodontic patients from whom two premolars were to be extracted. Daily mouthrinses with 0.05 % NaF for 2 weeks increased the fluoride content of the outer enamel layer (≈ 5 μm) by 15.9%. One rinse with 0.2% NaFincreased the fluoride content by 5.8%. Amajor part of the fluoride deposited was soluble in alkali. No significant uptake of fluoride in a second enamel layer (≈5 μm) was found. It is suggested that the alkali-soluble fraction of fluoride, representing the major part of the fluoride retentate, might serve as a significant reservoir of fluoride, and is perhaps a factor of prime importants concerning its cariostatic effect.