Fluoride Release and Uptake from Glass Ionomer Cements and Composite Resins


Patrícia WEIDLICH1
Letícia Algarves MIRANDA2
Marisa MALTZ1
Suzana Maria Werner SAMUEL2
 

1Departamento de Odontologia Preventiva e Social,
2Departamento de Odontologia Conservadora, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil


Braz Dent J (2000) 11(2): 89-96 ISSN 0103-6440

Introduction | Material and Methods | Results | Discussion | Conclusions | Acknowledgments | Resumo | References


The aim of this investigation was to evaluate fluoride release and uptake from 4 glass ionomer cements (GICs) - Vitremer (VIT), Fuji II LC (FII LC), Fuji IX (FIX), Chelon Fill (CHE) - and 2 composite resins (CRs) - Heliomolar (H) and Zeta-100 (Z-100). Eight discs (8 mm x 2 mm) were made of each material and were stored in plastic vials containing artificial saliva at 37ºC. In group 1 (N = 3), the specimens were immersed in artificial saliva which was changed daily for 25 days. In group 2 (N = 5), besides receiving the same treatment as group 1, the specimens were immersed, after 24 hours, in a fluoride solution (1% NaF) for 1 min before daily saliva change. An ion-specific electrode (9609 BN-Orion) connected to an ion analyzer (SA-720 Procyon) was used to determine the amount of fluoride released at days 1, 2, 5, 10, 15, 20 and 25. Data were analyzed using two way ANOVA and Friedman's test. GICs released more fluoride during the first day and after this period the mean fluoride released decreased. Composite resin H released fluoride during the first day only and Z-100 did not release fluoride. In terms of NaF treatment, CRs did not show fluoride uptake, whereas the GICs showed fluoride uptake (VIT=FII LC=CHE>FIX).


Key Words: fluoride release, fluoride uptake, glass ionomer cements, composite resins.


Introduction

The release of fluoride is one of the main advantages of glass ionomer cements. Both in vitro (Forsten, 1990; Creanor et al., 1994) and in vivo studies (Hatibovic-Kofman and Koch, 1991) have shown this property, which makes glass ionomer cements a filling material with anticariogenic effects. However, fluoride release can be influenced by factors such as solubility (Forsten, 1977), fluoride content of the material (Forsten, 1977), porosity (De Schepper et al., 1991), nature of the dissolving medium (El Mallakh and Sarkar, 1990) and temperature (Forsten, 1990). Although the pattern of fluoride release changes a lot according to the methodology used, researchers agree that greater quantities of fluoride are released during the first days and after that the level of fluoride released falls to a constant level (Forsten, 1990; De Schepper et al., 1991; Hatibovic-Kofman and Koch, 1991; Creanor et al., 1994).

Investigations have shown that besides releasing these ions, glass ionomer cements also take up fluoride from the oral environment. Hatibovic-Kofman and Koch (1991) reported that glass ionomer cements take up the fluoride from fluoride dentifrice and release it, which means that this material might be looked upon as a "rechargeable slow release fluoride system". The presence of fluoride in the oral environment guarantees long-term fluoride release, since this fluoride binds chemically to glass ionomer cements and is gradually released. Thus, a continuous release-uptake-release process occurs in situ (Hatibovic-Kofman and Koch, 1991; Creanor et al., 1994).

Composite resins are also widely used in Dentistry as filling materials. Although they have better aesthetic characteristics than glass ionomer cements, composite resins do not release fluoride. Some manufacturers add fluoride to composite resins for an anticariogenic effect. Studies have shown that composite resins release fluoride for a shorter period of time compared to glass ionomer cements (Forsten, 1990). Conflicting results are reported concerning fluoride uptake from composite resins which contain fluoride in their composition (Takahashi et al., 1993; Young et al., 1996).

Studies which evaluate fluoride uptake and release usually test fluoride release for a certain period of time, and usually the specimens are submitted to the exposure of fluoride only after the completion of the fluoride release process. However, the release-uptake-release process which occurs in the oral cavity is a dynamic process in which release and uptake occur simultaneously. The aim of this study was to compare the amount and pattern of fluoride release and uptake from glass ionomer cements and composite resins exposed to fluoride solutions.


Material and Methods

Four glass ionomer cements and two composite resins were tested to determine the amount of fluoride released into artificial saliva. Materials, batch numbers and manufacturers are listed in Table 1.

Eight specimens of each material were prepared. All materials were handled according to manufacturers' instructions. Immediately after mixing, the materials were placed in a plastic mold 8 mm in diameter and 2 mm in height. All specimens were made in the same mold to guarantee the same total area of 1.50 cm2. Setting of all materials occurred between two glass plates with hand pressure. Light-activated materials (VIT, FII LC, H and Z-100) had upper, lower and lateral surfaces of the disc polymerized at 3 sites for 40 s each using a visible light-curing unit, resulting in a final polymerization time of 6 min for each specimen. Chemically set glass ionomer cements remained between the glass plates for 10 min. Specimens were removed from the mold and all discs were submitted to standard polishing using Soflex discs (3M Dental Products, St. Paul, MN). FIX and CHE discs were polished after 24 h, while the other glass ionomer cements and composite resins were polished immediately after removal from the mold. All specimens were kept in a humidifier for 24 h (37oC, 100% relative humidity) and then placed in polyethylene tubes containing 4 ml of artificial saliva. After 24 h, five of the eight specimens of each material were removed from the tube, dried, immersed in a 1000 ppm fluoride solution for 1 min, dried and placed in another tube containing 4 ml of artificial saliva. This procedure was repeated daily for 25 days (group 2). The other three specimens of each material received a similar treatment, although they were not immersed in the fluoride solution (group 1).

Fluoride ion concentration of the artificial saliva on days 1, 2, 5, 10, 15, 20 and 25 was determined by adding 1 ml of Tisab II to 1 ml of artificial saliva, using a fluoride specific electrode (Orion 96-09, Orion Research Inc., Boston, MA) and an ion analyzer (Orion SA720, Orion Research Inc.). The 4-ml sample solutions were stored in a refrigerator at about 4ºC before analysis. Two samples of each tube containing artificial saliva were measured. If the variation between these two samples was higher than 5%, a third sample was measured.

Before making fluoride measurements, three vials containing artificial saliva and Tisab II were tested to determine baseline fluoride concentration of the artificial saliva. The mean baseline concentration (0.034 ppm) was subtracted from each concentration obtained from the samples. Total fluoride release was divided by the area of the disc (1.50 cm2), giving all recorded units in µg F/cm2.

Data were analyzed using two-way ANOVA and Friedman's test.


Results

In group 1 (no fluoride exposure), GICs released more fluoride during the first day and after this period the mean fluoride released decreased. Composite resin H released fluoride during the first day only. The amount of fluoride released by this resin was significantly lower than that released by the GICs (P<0.05). Resin Z-100, which does not have fluoride in its composition, did not release fluoride (Table 2).

Regarding NaF treatment, CRs did not show fluoride uptake, whereas the GICs showed fluoride uptake. VIT, FII LC and CHE showed a similar pattern of fluoride uptake during the 25-day period. These materials released significantly more fluoride (P<0.05) after the exposure to NaF solution compared to without immersion in the NaF solution. FIX was statistically similar to the other GICs and to the fluoridated composite resin. Composite resins released significantly less fluoride after exposure to NaF than VIT, FII LC and CHE


Discussion

According to the nomenclature proposed by McLean et al. (1994), the materials tested in this study included two resin-modified glass-ionomer cements (VIT and FII LC), two glass ionomer cements (FIX and CHE), a fluoride containing composite resin (H) and a composite resin without fluoride in its composition (Z-100).

In agreement with previous studies, the present results showed that exposure of GICs to a solution containing fluoride allows the materials to take up fluoride and subsequently release it (Hatibovic-Kofman and Koch, 1991; Diaz-Arnold et al., 1995; Forsten, 1995, 1998; Rothwell et al., 1998). However, different from other studies, this study tested fluoride release and uptake from GICs and CRs at the same time, without exhausting fluoride release prior to the immersion in the fluoride solution. It is important to test GICs fluoride release and uptake at the same time because this experimental design simulates the oral cavity dynamics more accurately. We observed significantly greater fluoride release in almost all GICs tested after NaF solution immersion when compared to the fluoride release rate of the specimens which were not immersed in the fluoride solution. This dynamic process of uptake and release was maintained throughout the experimental period. This experiment, like others (De Schepper et al., 1991; Creanor et al., 1994), showed that the greatest fluoride release occurred during the first 24 h. After this period, fluoride release decreased, showing very low levels after 25 days.

It was observed that both resin-modified glass-ionomer cements (VIT and FII LC) and one glass ionomer cement (CHE) had similar fluoride uptake after exposure to NaF solution, in agreement with Takahashi et al. (1993), Creanor et al. (1995) and Rothwell et al. (1998) who reported no difference in fluoride release and uptake from different GICs.

It is important to consider that different metodology used in the studies, including specimen size, media used to measure fluoride release and uptake, quantity of media used to measure fluoride and different methods to measure fluoride release, are responsible for the high numerical differences found among several studies. Thus, comparisons must be made considering the behavior of materials rather than the absolute amount of fluoride released and uptaken.

Data obtained from composite resins showed that the fluoride containing resin (H) released fluoride only on the first day. This amount was minimal compared to the GICs. This low fluoride release rate was also found in other studies (Forsten, 1990). Composite resin Z-100 showed no fluoride release. We also observed a low fluoride uptake by both composite resins. This was attributed to a cross-over contamination rather than a true fluoride uptake, since specimens were just dried after being removed from the 1% NaF solution. The uptake from CRs was most probably due to surface-retained fluoride. The CRs system is a hydrophobic medium, so that ion exchange from the fluoride component is reduced (Young et al., 1996). The low fluoride uptake by CRs found in this study is in agreement with Young et al. (1996), who used Tetric composite, which has the same fluoride-containing filler substance (ytterbium trifluoride _ YbF3). Takahashi et al. (1993) also reported some release after fluoride exposure for APH Prisma, a composite resin similar to Z-100, which also does not have fluoride in its composition.

Artificial saliva was used instead of deionized water to better simulate the oral environment. However, fluoride release in artificial saliva is lower then in deionized water. This fact can explain the lower fluoride release rate found in this study compared to studies using deionized water (El Mallakh and Sarkar, 1990). Moreover, Damen et al. (1996) reported that fluoride uptake is affected by a coating which forms on the cement when it is exposed to saliva. The pH of the dissolving medium also influences fluoride release (Diaz-Arnold et al., 1995). Both conventional and resin-modified GICs increased fluoride release in an acidic environment (Forsten, 1995). Artificial saliva used in this study had a pH of 6.8 which also corroborates the low fluoride release found.

Intragroup variability of the GICs specimens was frequently found in the present and other studies (De Schepper et al., 1991). Since specimens were prepared individually, this variability can be attributed to the instability of the setting reaction of GICs during the early setting period, to slight variations in setting time, as well as to differences in the mixture process itself.

A slow release of fluoride from dental materials may have clinical implications in vivo. Fluoride release from GICs restorations, resulting from a continuous fluoride uptake process, increases the fluoride concentration in saliva (Koch and Katibovic-Kofman, 1990; Katibovic-Kofman and Koch, 1991) and in adjacent dental hard tissues (Gilmour et al., 1997; Tam et al., 1997). Thus, continuous small amounts of fluoride surrounding the teeth decrease demineralization of enamel (Benelli et al., 1993), dentin (Tam et al., 1997) and cementum (Gilmour et al., 1997). Fluoride release from CRs is minimal when compared with GICs and in this study fluoride release occurred only during the first 24 hours. Some studies have shown that this low fluoride release rate from CRs can reduce enamel demineralization in vitro (Ögaard et al., 1992) as well as dentin demineralization in situ (Dijikman and Arends, 1992). However, the prevalence and depth of artificial caries-like lesions around CRs restorations are significantly higher compared to GICs restorations (Gilmour et al., 1997). This study suggests that clinically glass ionomer cement restorations are more effective in preventing further demineralization than are composite resins.


Conclusions

1. Glass ionomer cements release fluoride.

2. Glass ionomer cements take up fluoride from a 1000 ppm NaF solution and subsequently release it.

3. Composite resins which contain fluoride release minimal amounts of fluoride compared to glass-ionomer cements and take up less fluoride from a 1000 ppm NaF solution than glass ionomer cements.


Acknowledgments

This study was supported by the Research Foundation of Rio Grande do Sul (FAPERGS), process 95/60377.3.


Resumo

Weidlich P, Miranda LA, Maltz M, Samuel SMW. Liberação e absorção de flúor de cimentos de ionômero de vidro e resinas compostas. Braz Dent J 11(2): 89-96, 2000.

O objetivo dessa investigação foi avaliar a liberação e absorção de flúor de 4 cimentos de ionômero de vidro (CIVs) - Vitremer (VIT), Fuji II LC (FII LC), Fuji IX (FIX), Chelon Fill (CHE) - e duas resinas compostas (RCs) - Heliomolar (H) e Zeta-100 (Z-100). Foram confeccionados oito discos (8 mm x 2 mm) de cada material e armazenados em recipientes plásticos contendo saliva artificial a 37ºC. No grupo 1 (N = 3), os espécimes foram imersos em saliva artificial, a qual foi trocada diariamente durante 25 dias. No grupo 2 (N = 5), além de receber o mesmo tratamento dispensado ao grupo 1, os espécimes foram imersos, após 24 horas, em solução fluoretada (NaF a 1%) durante 1 minuto previamente à troca diária de saliva artificial. A quantidade de flúor liberada nos dias 1, 2, 5, 10, 15, 20 e 25 foi assessada através de um eletrodo específico para flúor (9609 BN-Orion) conectado a um analisador de íons (SA-720 Procyon). Os dados foram analisados através de ANOVA de duas vias e do teste de Friedman. Os CIVs liberaram maior quantidade de flúor nas primeiras 24 horas, após esse período, a quantidade média de flúor liberado decresceu. A resina composta H liberou flúor apenas durante as primeiras 24 horas, enquanto que a Z-100 não liberou flúor. Com relação ao tratamento com solução fluoretada, as RCs não absorveram flúor, ao contrário dos CIVs (VIT=FII LC=CHE>FIX).


Unitermos: liberação de flúor, absorção de flúor, cimentos de ionômero de vidro, resinas compostas.


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Correspondence: Dr. Marisa Maltz, Departamento de Odontologia Preventiva e Social, Universidade Federal do Rio Grande do Sul, Ramiro Barcelos 2492, 90035-003 Porto Alegre, RS, Brasil. E-mail: mmaltz@vortex.ufrgs.br


Accepted March 29, 2000
Eletronic Publication october, 2000


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