Comparative study of fluoride released and recharged from conventional pit and fissure sealants versus surface prereacted glass ionomer technology.

CONTEXT: The fluoride release of sealants in vitro shows a marked decrease. Giomers are distinguishable from manufactured resin-based sealants and contain prereacted glass-ionomer particles (PRG). AIMS: To compare the amounts of fluoride released from the main pit and fissure of a resin-based sealant with that from a Giomer and to assess the abilities of the sealant and the Giomer to recharge when exposed to regular use of fluoride rinse.
MATERIALS AND METHODS: The readings for the fluoride concentration were carried out for 60 days using a fluoride ion-specific electrode. After this period, the samples were recharged using a fluoride mouth rinse. The amount of fluoride released after this recharge was determined for 5 days. The data were analyzed using Student's t- and analysis of variance tests.
RESULTS: In general, all materials presented higher fluoride release in the first 24 h; G1 and G4 showed a higher fluoride release in this period. On the other hand, G3 and G1 presented the most constant fluoride release until the 8(th) day, wherein all the sealants considerably decreased in the amount of fluoride released.
CONCLUSION: G1 and G3 released higher concentrations of fluoride, although no significant differences were found. Giomers recharged in the first 24 h after polymerization presented an improved and sustained fluoride release.

INTRODUCTION

Fluoride is recognized as an anticarcinogenic agent and has been added to different products; fluoride-releasing dental materials have been developed, attracting the interest of researchers.[12]

Occulsal surfaces of teeth in children constitute 50% of the sites commonly affected by caries. Therefore, pits and fissures of molars are the most susceptible. Pit and fissure sealants were introduced in the 1960s to prevent occlusal dental caries.[34]

Actually, two types of sealants are available: Resin-based and glass-ionomer cements. The sealants have progressed from the first generation, which were activated with ultraviolet light, to the second generation, which were autopolymerized sealants; the third generation were activated by visible light, and the fourth generation contain fluoride.[56]

Giomers combine the advantages of both glass-ionomer cements and resins; Moreover, they are distinguished by the fact that they also contain prereacted glass-ionomer particles (PRG), particles of fluorosilicate glass that have been reacted prior to being incorporated into the resin.[3]

The purpose of this study was to compare the amount of fluoride released from the pits and fissure of a sealant-based resin with that from fluoride-releasing Giomer, thus assessing their ability to recharge when exposed to a fluoride mouth rinse.

MATERIALS AND METHODS

Sample preparation

The materials used in this study were a Giomer and three fluoride-releasing sealants divided into 4 groups with eight samples of each sealant: G1 — BeautiSealant (Shofu, Japan); G2 — Clinpro (3M ESPE, USA); G3 — Helioseal F (HF) (Ivoclar Vivadent, Liechtenstein); and G4 — UltraSeal XT (US) plus (Ultradent Products, USA).

The materials were handled according to the manufacturers’ instructions and 32 samples were prepared. The samples consisted of eight blocks of each sealant with 5 mm width and 1 mm thickness; the samples were placed in cavities with similar measures in a Teflon matrix.[7]

All samples were polymerized using a LED device (Elipar, 3M ESPE) for 40 s, verifying with a radiometer that the intensity of light emitted has a minimum value of 400 mW/cm2.

The polymerized samples were removed from the matrix and were then stored in plastic bottles with 5 ml of deionized water. The samples were conserved at 37°C for 60 days and measured on days 1, 2, 4, 8, 28, and 60, which is similar to the time intervals used in previous studies.[89]

Instrumentation and reagent solutions

To determine the amount of fluoride in sealants, it was necessary to use an ion-selective electrode for sodium fluoride (model 1011, Hanna Instruments, USA) and a potentiometer (model 3222, Hanna Instruments). The total ionic strength adjustment buffer (TISAB) solution was used to keep the pH stable and to prevent the fluoride ion producing complexes with different cations.[8910]

Potentiometer calibration

The fluoride solutions used in this study were prepared in concentrations of 1, 2, 10, 100, and 1000 ppm. TISAB was used to obtain a calibration slope with fluoride solutions; equal volumes of fluoride solution and TISAB (25 ml of each) were placed and mixed in a 100 ml plastic glass; the device was calibrated until the readings were reached.

Fluoride determination

At the end of each period, the blocks were removed from their respective recipients, and each sample was washed with 1 ml of deionized water in the bottle that originally contained it. Five milliliters of solution was used to store the sample and 1 ml was used to wash the sample, giving a total of 6 ml that was mixed with 6 ml of TISAB, because this solution works in a proportion of 1:1. The sample was placed in a new 5 ml plastic bottle with deionized water.

The readings were performed under magnetic stirring for 3 min with the electrode immersed in the solution where the sample had been previously. The values of the readings were expressed in parts per million.[91011]

After 60 days of monitoring, the samples were recharged using a mouth rinse. This solution contains sodium fluoride in 300 ppm (Colgate Plax Kids, USA). The samples were immersed in this solution for 1 min and were subsequently rinsed with deionized water for 1 min. The fluoride released in the samples after recharge was determined daily for 5 days.[12]

Another control group was created to observe the behaviors of Giomers when they are recharged in the first 24 h after polymerization; in contrast, the other groups were recharged after 60 days. Eight samples of this group were recharged daily for 5 days.

The data were analyzed with analysis of variance (ANOVA) and the Student's t-test for related samples using the 21st version of the statistical program SPSS Statistics (IBM, USA).

RESULTS

The pattern of fluoride release according to the time intervals is represented in Table 1 and started with high concentration during the first day for all sealants, with a value for G1 of 5.1 ppm, which makes this Giomer the material with the highest fluoride concentration, and for G2 a value of 2.7 ppm, which makes it the sealant with the lowest fluoride concentration; the groups G3 and G4 presented fluoride releases of 3.0 and 4.8 ppm, respectively.

Table 1

Fluoride releases in sealants

From the presented data, it appears that all materials released different levels of fluoride, and the highest fluoride release of each material occurred on the 1st day. From the 2nd day, a slow, steady decline in fluoride release began and continued until day 60 with the exception of G4, which showed a marked decline to a value of 1.2 ppm. Figure 1 clearly shows the amount of fluoride released for each sealant evaluated versus time.

Figure 1

Fluoride released by each of the sealants evaluated for 60 days: (a) Fluoride released by G1; (b) Fluoride released by G2; (c) Fluoride released by G3; (d) Fluoride released by G4

The ANOVA showed significant differences between the amounts of fluoride of the four materials [Table 2]. However, the interaction between time and material shows that the fluoride release is not constant with time for all materials under study.

Table 2

ANOVA test

When we found statistically significant differences with respect to the amount of fluoride release, we decided to evaluate the behavior of materials in the established periods using the Student's t-test for related samples. Differences were observed in relation with time. G1 showed significant differences between days 1 and 2 with values for Student's t-test of t = 6.898 and P = 0.000, which show a marked decrease in fluoride release from the Giomer after the second day, with approximately half of fluoride release occurring in the first 24 h. There was also marked decrease between days 8 and 28 (t = 4.326, P = 0.003) due to day 28 just releasing 1.1 ppm.

G2 showed significant differences between days 1 and 8 (t = 6.848 and P = 0.000) and between days 1 and 28 (t = 7.699, P = 0.000). This sealant did not present differences between days 1 and 2; it was the only one that had increased fluoride release for the 2nd day. A difference was observed between days 2 and 8 (t = 15.815, P = 0.000) because for day 8 G2 released only 1.1 ppm.

G3 presented statistically significant differences when comparing the amount of fluoride released between days 1 and 4 (t = 2.922, P = 0.022); during the first 3 days a more constant fluoride release was presented. There were differences between days 1 and 8 (t = 4.693, P = 0.002); the fluoride released on day 8 was reduced to almost a third. There were differences especially between days 1 and 60 (t = 5.539, P = 0.001) as after 60 days only the sealants based on resin released more than 1.0 ppm.

G4 showed differences between the first and 2nd days (t = 7.877, P = 0.000); it was the sealant that presented the most marked decrease for the 2nd day. There were differences between days 1 and 8 (t = 9.504, P = 0.000), between days 1 and 28 (t = 9.540, P = 0.000), and between days 1 and 60 (t = 9.860, P = 0.000); on the 1st day 4.8 ppm was released but from the 2nd day onward the amount released was never higher than 1.2 ppm.

On day 60, when recharges began with a fluorinated rinse for 1 min, it can be seen that the recharge did not induce any increase in the resin-based sealants. In the same way, any change in the fluoride concentration of Giomers was detected. Figure 2 illustrates the fluoride release of each sample after being recharged.

Figure 2

Fluoride release of sealants after of recharge with sodium fluoride at 250 ppm

However, the control group of Giomer that was recharged from the first 24 h after being polymerized presented an improved and sustained fluoride release during the 5 days of recharging daily [Table 1].

DISCUSSION

The minimum amount of fluoride that must be released to inhibit demineralization and promote the remineralization has not been precisely known.[131415] Some authors report that this value would be between 0.02 and 0.06 ppm,[16] while others mentioned that a concentration of 0.2 ppm has a significant effect of preventing caries.[7] However, the use of dental materials with the highest and prolonged fluoride release is preferable because when the fluoride ion is present in the saliva and biofilm, the enamel solubility is low.[1718]

Based on the results of this study, it can be said that resin-based sealants release between 3.0 and 5.0 ppm during the first 24 h, from the 2nd to 4th day an average of 2.0 ppm, and only 1.0 ppm from day 8 to day 60, which suggests further development of materials that can maintain a greater and more constant fluoride release to improve preventive treatments.

Urquía et al.[7] in 2005 reviewed several fluoride-releasing materials, among which there were 2 resin-based sealants, which were US XT Plus and HF. They observed that on the 1st day both sealants released 0.88 ppm, being the highest concentration, and reported a slight increase for the US on day 7 with a value of 1.2 ppm and 0.2 ppm for HF. In contrast, our study reported the highest fluoride release for all sealants in the first 24 h and higher values for both sealants of 3.0 ppm for HF and 4.8 ppm for US during the first 24 h and a marked decreased from the 2nd day.

The results of some authors match with ours. Gómez et al.[8] in 2011 reported the highest fluoride release during the first 24 h for two sealants evaluated in this study, HF, with 6.57 ppm, and Clinpro, with 2.45 ppm. This study, though, reported for the sealant Fissurit F an extremely high value of 26.0 ppm for the 1st day and a marked decrease for the 2nd day with a value of 2.31 ppm. Therefore, it could be interesting consider this material for future investigations.

The release of fluoride in high quantities during the 1st h has also been observed in other similar studies regarding fluorinated resin sealants and other restorative materials containing fluorine.[119]

The particles of surface-PRG technology were reported to act as a fluoride reservoir that recharge with brushing or rinsing with fluoridated products.[20]

Itota et al.[21] conducted a study to compare two compomers and a Giomer (Reactemer paste) that shows higher concentrations. The specimens were exposed to 250 ppm fluoride solution for 1 h to recharge the materials; Itota et al. reported that Giomer released a great amount of fluoride compared with the other compomers, which showed an unchanged level after recharging. Similarly, in our study, the Giomer (BeautiSealant) shows greater amount of fluoride, with a value of 5.1 ppm during the first 24 h and a decrease to 2.1 ppm for the 2nd day. In this study the samples were exposed to a mouth rinse of 250 ppm after 60 days to recharge the materials but only for 1 min because this is the real time that kid is exposed to a solution with this amount of fluoride. In our study, the recharges after 60 days of observation did not show any significant differences in the amounts of fluoride released by the three resin-based sealants and the Giomer.

The fluoride released by the group recharged in the first 24 h was higher during the first 5 days compared with those released by sealants of the resin base and the Giomer that was recharged after 60 days. These results support the hypothesis that the materials manufactured with PRG technology provide better results when they are recharged immediately after being placed in the mouth.

CONCLUSIONS

All resin-based sealants and Giomer showed the greatest fluoride release in the first 48 h, which was then followed by a marked decrease.

The degree of fluoride released in vitro for the three resin-based sealants was slightly smaller than that for the Giomer during the 1st day of the study.

After 8 days of analysis, both the resin-based sealants and the Giomer showed minimum levels of released fluoride.

When the Giomer was recharged at 24 h of polymerization with a fluoride rinse of 250 ppm, it showed a greater and more sustained fluoride release.

The recharging with sodium fluoride at 200 ppm after 60 days of the study did not show significant differences with respect to the released amount of fluoride after this period.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.