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Original Article

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Bull. Tokyo dent. Coll., Vol. 45, No. 3, pp.173179, August 2004

INTRODUCTION

One of the key factors in preventing dentalcaries has been recognized to be increasingthe resistance of teeth to acid by encouragingthe development of re-mineralization mecha-nisms on the enamel surface. The daily topi-

cal application of a fluoride, such as sodiumfluoride (NaF), acidulated phosphate fluo-ride solution (APF), or stannous fluoride(SnF2), usually by the daily use of a fluoride-containing dentifrice, has been reported tobe of benefit both in professional clinics andself care. Pit-and-fissure sealants are also useful

COMPARISON OF SHORT-TERM IN VITRO FLUORIDERELEASE AND RECHARGE FROM FOUR DIFFERENTTYPES OF PIT-AND-FISSURE SEALANTS

HIROSHIKOGA, ATSUSHIKAMEYAMA*, TAKASHIMATSUKUBO,YOSHITOHIRAI* and YOSHINORITAKAESU

Department of Epidemiology and Public Health, Tokyo Dental College,1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan

* Third Department of Conservative Dentistry, Tokyo Dental College,

1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan

Received 18 October, 2004/Accepted for Publication 15 December, 2004

Abstract

Objective: The purpose of this in vitrostudy was to assess the effects of four commercialfluoride-containing pit-and-fissure sealants on caries prevention. Materials and Methods:Four sealants containing fluoride, Fuji III, Fuji III LC (GC Co., Tokyo), Teethmate F-1

(Kuraray Medical Co., Osaka) and Helioseal F (Vivadent Co., Liechtenstein) were usedto investigate fluoride release and recharge. Disk-shaped specimens prepared from eachmaterial were immersed in distilled water at a temperature of 37C. After seven days,acidulated phosphate fluoride solution (APF) was applied to each specimen, and it wasthen again immersed in distilled water for 14 days. We then determined how muchfluoride had been released into the immersing water. Fuji III LC was used with APFsolution to investigate the fluoride uptake. Results: Fuji III had the highest fluoriderelease, and Fuji III LC had the highest fluoride recharge. Helioseal F and TeethmateF-1 had almost no fluoride recharge. Fuji III LC/APF had a higher fluoride uptake toenamel than Fuji III LC. Conclusions: These results suggest that GIC-sealants in the oralcavity can serve as a fluoride reservoir and contribute to retaining a low fluoride level inoral fluids, thereby preventing caries.

Key words: Fluoride-containing pit-and-fissure sealant Fluoride releaseFluoride recharge Fluoride uptake Caries prevention

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J. Morita Co., USA) from the top and bottomfor 40 sec. After hardening, both the top andbottom acrylic were removed. Five disks wereshaped from each sealant material. Each pre-pared disk was immersed in 5 ml of distilled

water in a 10-ml plastic test tube and placedwithout agitation in an incubator at 37C. The5 ml of distilled water used for immersion waschanged every 24hrs.

3. Fluoride recharge of applied APF fromsealants

The sealant disks were removed from thetest tubes after immersion for seven days,

rinsed with distilled water, and immersed inacidulated phosphate fluoride solution (APF:9,050ppmF, pH3.8) in a 200-ml plastic beakerfor 4 min. The disks were then removed from

APF solution, re-rinsed with distilled water,and immersed in 5 ml of distilled water ina plastic test tube, enabling fluoride to bereleased. The immersing water was changedevery day and this procedure was repeatedover 14 days. The distilled water samples con-taining fluoride ions were kept in a refrigera-

tor at 4C until their fluoride concentrationscould be determined.

4. Fluoride ion concentration measurements

The concentration of fluoride ions releasedfrom the sealants was analyzed with a com-bination fluoride ion-selective electrode(Model 96-09BN, Orion Research Co., Cam-bridge, MA) connected to an ion-analyzer(EA920, Orion Research Co., Cambridge,MA). To determine the fluoride concentra-

tion, 0.1, 1.0, and 10 ppm standard solutionsof fluoride ions were prepared, and furtherstandard solutions of 0.05 and 0.02 ppm fluo-ride ions were used for low fluoride solutionsbelow 0.1ppm each time.

5. Fluoride uptake to bovine enamel treatedwith FIII L and FIII L/APF application

Five bovine anterior teeth were polishedwith a hearthstone powder and a polishingbrush for about one minute each and incisedbetween the tooth crown and root with a dia-mond cutter. Each tooth crown was divided

into four specimens to obtain a total of 20bovine enamel specimens. Five bovine enamel

specimens were randomly chosen, and filledwith the pit-and-fissure sealant, FIII L (light/chemical curing), according to the manufac-turers directions. Two groups consisting offive such bovine enamel specimens were pre-pared. In the first group, fluoride uptake tothe enamel was accomplished with FIII Lalone in the second group, APF was appliedseven days later. Five bovine enamel samples

were evaluated as the control.A bovine enamel specimen sealed with FIII

L was immersed in 5ml of 0.05M mono-

calcium phosphate saturated solution witha pH of 7.4 adjusted with 5M potassiumhydroxide10). This was used as artificial salivain a plastic test tube. The immersion solution

was changed everyday. In the APF applica-tion group, bovine enamel specimens wereimmersed in the APF solution for four min-utes seven days after immersion started,rinsed with distilled water, and re-immersedin the artificial saliva. In both groups, immer-sion in the artificial saliva was maintained over

14 days.

6. Bovine enamel specimen sampling aftertreatment with FIII L and FIII L/APFapplications and determination of

fluoride uptake

After the immersion experiments, the pit-and-fissure sealants were firmly yet carefullyremoved from the bovine enamel specimensof both groups with a spatula. After rinsing

with distilled water, a window (55 mm) was

made on the enamel surface of the specimenswith dental wax, and the specimen was fixedto an acrylic rod (8-mm diameter, 11-cmlong). The enamel was sampled with acidetching according to Ohkawas method13).The enamel specimens were immersed in0.4ml of 0.5M perchloric acid in a plastic testtube for 10sec and then neutralized by add-ing 1.6ml of 0.5M sodium tricitrate. Thesame enamel specimens were continuouslysubjected to further acid treatment throughimmersion for 20 and then 30 sec. The fluo-ride concentrations in the sampling solutions

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were analyzed with the fluoride ion electrodemethod using a buffer solution, 0.5M per-chloric acid, and 0.5M sodium tricitrate (1:4)as adopted by Ohkawa13). The calcium con-centrations in the enamel sample solutions

were measured with atomic absorption spec-trometry (ASS: Model 508, Hitachi). Theamount of enamel in each sample was calcu-lated using a content of 36% calcium and 2.95specific gravity for the values in bovine

enamel. The area of the enamel specimen wasdetermined with the tin foil method13).

7. Statistical analysis

The means and standard deviations were cal-culated for the groups and evaluated by analy-sis of variance (Tukey Kramer test, StatView-J5.0). A value of p0.05 was regarded assignificant.

RESULTS

Figure 1 plots the cumulative release offluoride ions from the four types of fluoride-containing pit-and-fissure sealants. APF solu-tion was applied on the seventh day. Thecumulative release of fluoride ions up to theseventh day was the highest for FIII at23745.2 (SD) g/cm2, FIII L and TF1 hadsimilar levels of approximately 53g/cm2,and HSF had the lowest value of 3.72.8g/cm2. As we can see in Fig. 2, the rate at whichfluoride ions were released from FIII was

71.912.6g/cm2/day on the first day, and itrapidly decreased to 19.33.3g/cm2/dayon the fifth day. The rates at which fluorideions were released from FIII L and TF1 hadsimilar patterns. The initial fluoride releaserates ranged from 17.218.4g/cm2/day, anddecreased to a third (4.04.7g/cm2/day) ofthis on the fourth day, indicating that fluorideions were released more slowly from FIII Land TF1 than from FIII.

We estimated the release of fluoride ionsfrom the four sealants after APF had beenapplied on the seventh day and confirmedthat fluoride was recharged in the FIII andFIII L GIC-sealants, although this was notobserved in the TF1 or HSF resin sealants.Moreover, fluoride recharge was 1.5-foldgreater in FIII L (light/chemical sealant74.19.4g/cm2) than in FIII (conventionalsealant, 58.79.5g/cm2), and the differ-ence was statistically significant (p0.05, see

Fig. 3). Both instances of fluoride rechargeswere retained for about one day and it thentook three days to reach the same release rateas that before APF had been applied.

Figure 4 plots fluoride concentrations inenamel layers in the GI, GII, and controlgroups. These concentrations for GI and GII

were significantly higher than those of thecontrol groups (p0.05). The fluoride con-centrations in GI were very high, i.e.,10,1004,570 (SD) ppm in the first layer,6,0703,430 ppm in the second layer, and3,3501,840 ppm in the third layer. The

Fig. 1 Cumulative fluoride-release from four differentpit-and-fissure sealants

Fig. 2 Fluoride-release from each fluoride-containingpit-and-fissure sealant in vitro

H. KOGAet al.

120

100

80

60

40

20

0

Days

1 2 3 4 5 6 7 8 9 10 11 12 13 14

FIII

HSF

FIII L

TF1

APF application

Fluoriderelease(g/cm

2)

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400

300

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FIII

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FIII L

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Cumulativefluoride(g/cm2)

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fluoride concentration in GII was about13,9002,390 (SD) ppm in the first layer,8,5503,260 ppm in the second layer, and3,8701,620 ppm in the third layer. Themean fluoride uptake to the enamel surface

was slightly higher in GII than GI, but therewere no statistically significant differences.

DISCUSSION

The fluoride release rates and periods offluoride-containing pit-and-fissure sealantsare clinically important in establishing to

what extent dental caries can be preventedand whether they will recur in the boundary.

We evaluated the fluoride released from fourtypes of fluoride-containing pit-and-fissuresealants in this study, fluoride recharge

resulting from APF application, and fluorideuptake to enamel treated with FIII L/APF invitro, to evaluate their clinical significance inpreventing caries.

Since conventional GIC (FIII) is extremelysensitive to water, GIC that has been chemi-cally polymerized after being used in fillings isdetached if water and saliva contact it, sug-gesting that the rate at which fluoride ions arereleased is increased due to it detaching. AsFIII L is light-hardening due to resin poly-merization (HEMA), the degree to which itdetaches is less than that of FIII, resulting in

fluoride being released more slowly. Thismeans that because FIII L is less sensitive to

water it retains much more AFP/FIII.We confirmed that fluoride is released

from glass ionomer/resin pit-and-fissure seal-ants for long periods. We found a markedrecharge after applying APF to both the con-

ventional and autohardening GICs used for

filling materials11)

. In the present study, theconcentration of fluoride ions released froma light/chemical GIC sealant (FIII L) decreased

to about a third immediately after APF wasapplied, which agreed with these results.

Similar results when examining short-termfluoride ion release and fluoride recharge(APF, NaF, SnF2) in GIC materials have beenreported, but the reported recharge of fluo-ride ions from the application solutions usedin dental materials has been very low for NaF

within the neutral pH range and it has beenhighly dependent on pH4).

In the 1990s, Arends and Christoffersen1)

and Featherstone6)proposed that dental caries

could be prevented on superficial layers ofenamel by inhibiting demineralization undercommon ions such as calcium ions and phos-phate ions and by promoting remineraliza-tion under fluoride ions on the surface. Theyalso stated that significant remineralizationoccurred even at very low concentrationsof fluoride ions (0.030.05 ppm) in the oralcavity. Consequently, fluoride in dental mate-

Fig. 4 Fluoride uptake (meanS.D.) to bovine enamelwith Fuji III LC (GI) and Fuji III LC/APF (GII)

Fig. 3 Comparison of fluoride recharge (FR, meanS.D.) after APF was applied for 4 min.

FR is defined as the difference in fluoride releasebetween that at 7 days and that at 8 days. *p0.05

FLUORIDE RELEASE AND RECHARGE FROM SEALANTS

20,000

16,000

12,000

8,000

4,000

01st layer

FIII L/APF-treated group (GII)

FIII L-treated group (GI)

Control

2nd layer 3rd layer

Fluorideconcentration(ppm)

100*

*

FIII FIII L HSF TF1

80

60

40

20

0

FR(g/c

m2)

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rials that contributes to the release of fluorideions is very important, both locally andthroughout the entire oral cavity. However, inthis study and many others, examining therelease of fluoride ions from pit-and-fissuresealants and fluoride-containing materialshas been done in batch systems with distilled

water in vitro, resulting in limitations in evalu-ating the dynamics of fluoride ions emanat-ing from these materials. Therefore, it is nec-essary to examine the dynamics of fluorideions under conditions that are the same as theoral environment, for example, through study-

ingpH cycling and the in situoral system5).

Ripa

14)

suggested that there were limita-tions with intentionally adding fluoride todental materials and devices to prevent dentalcaries from forming or enamel from deminer-

alizing. These limitations extended to delivery

of drugs (including fluoride) to prevent oraldiseases (including those of soft and hardtissues) because the clinico-epidemiologicalfindings were inconclusive14).

The preventive effects the glass-ionomerpit-and-fissure sealant (FIII), were surveyed

clinico-epidemiologically for three years bycovering the permanent teeth of 91 childrenaged 410 years without caries with FIII 9).They found that the DMFT value decreasedto 66.5%. Furthermore, clinically reapplyingglass-ionomer would be sufficiently simplefor the public health sector, and its effectsin preventing dental caries in children areundeniable.

We rejected the null hypothesis that there islittle difference in fluoride recharge after APF

treatment on the seventh day between seal-ants (Fig. 3), because we found the fluoriderecharge in the FIII and FIII L GIC sealantsto be much higher than that in the TF1 andHSF resin sealants (p0.05). The fluoriderecharge in FIII L was also significantly higherthan that in FIII (p0.05). Therefore, we con-firmed that GIC sealants serve as fluoridereservoirs in this experiment. In relationto this, we also demonstrated that the acid-resistance in enamel treated with GIC sealanthad been greatly improved8).

We did not reject the null hypothesis that

fluoride uptake to the enamel surface byFIII L was almost the same as that with FIII L/

APF treatment on the seventh day, becausethere were no significant differences betweenthe two fluoride concentrations. However,the fluoride concentration in each layer ofenamel with FIII L/APF treatment (GII)tended to be slightly higher than that withFIII treatment (GI), although both these fluo-ride levels were extremely high. Regardingthe fluoride uptake in enamel with resin seal-ants (MF-MMF co-polymerization polymer),Tanaka et al.reported that the concentrationof total fluoride was ca. 3,500ppm on a 10-m

superficial layer, that KOH-soluble fluoride(non-bound) was 2030%, and that boundfluoride was 7080% on layers up to 60m16).These results were significantly higher thanthose in the control group. Kawai et al.obtained the same results for another com-posite resin they investigated7).

Our present study concurred with theseprevious results and found that fluoride-recharge from pit-and-fissure sealants andfilling materials on the surface of teeth

occurred within a short time and that theirapplication to teeth increased acid resistanceon the surface.

In the future, we should run clinico-epide-miological studies and in vivoexperiments toevaluate the effects of fluoride-containingsealants on preventing caries.

CONCLUSIONS

Of the four types of pit-and-fissure sealants,conventional GIC (FIII) had the highest rateof fluoride release; a similar release pattern

was observed in GIC pit-and-fissure sealant(FIII L) and resin sealant containing fluoridereleasing polymer (TF1). The rate at whichfluoride was released was reduced to about athird of the initial level within a few days, andrelease continued slowly thereafter. The fluo-ride recharge in FIII L when APF was appliedto the GIC sealant was significantly higherthan in FIII (p0.05). These results suggestthat GIC-sealants in the oral cavity reservoirs

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differ in their properties and that they cancontribute to low levels of fluoride beingretained in the oral fluid, thereby preventingcaries.

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11) Kupietzky, A., Houpt, M., Mellberg, J. andShey, Z. (1994). Fluoride exchange fromglass ionomer preventive resin restorations.Pediatric Dent16(5), 340345.

12) Mount, G.J. (1986). Longevity of glass

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Reprint requests to:Dr. Hiroshi KogaDepartment of Epidemiology andPublic Health,Tokyo Dental College,1-2-2 Masago, Mihama-ku,Chiba 261-8502, Japan

FLUORIDE RELEASE AND RECHARGE FROM SEALANTS