|Year : 2011 | Volume
| Issue : 1 | Page : 39-45
Effect of low-concentration daily topical fluoride application on fluoride release of giomer and compomer: An in vitro study
KS Dhull1, B Nandlal2
1 Department of Pedodontics and Preventive Dentistry, Institute of Dental Sciences, Bhubaneswar - 751 003, Orissa, India
2 Department of Pedodontics and Preventive Dentistry, JSS Dental College and Hospital, JSS University, Mysore, Karnataka, India
|Date of Web Publication||23-Apr-2011|
K S Dhull
Department of Pedodontics and Preventive Dentistry, Institute of Dental Sciences, Bhubaneswar - 751 003, Orissa
| Abstract|| |
Aims and Objective: To determine the effect of low-concentration daily topical fluoride application on fluoride release of Giomer and Compomer and to compare the amount of fluoride release from Giomer to that of Compomer. Materials and Methods: Forty-eight specimens of each Giomer and Compomer were divided into four treatment groups, namely, control group, fluoridated dentifrice (500 ppm) once-daily group, fluoridated dentifrice (500 ppm) twice-daily group and fluoridated dentifrice (500 ppm) once-daily + fluoridated mouthwash (225 ppm) group. Each specimen was suspended in demineralising solution for 6 h and remineralising solution for 18 h. Fluoride release was measured in both the demineralising solution and the remineralising solution daily for 21 days. Total daily fluoride release for each specimen was calculated by adding the amount released in the demineralising solution to that released in the remineralising solution. Results and Conclusion: The fluoride release (ppm) was found to be higher in Giomer when compared with Compomer. The fluoride released from Giomer and Compomer was significantly higher in the acidic demineralising solution than in the neutral remineralising solution. It was found that increasing fluoride exposure significantly increased fluoride release from Giomer and Compomer. It was found that the fluoride release from the subgroups of Giomer and Compomer was in the following order: fluoridated dentifrice twice-daily > fluoridated dentifrice once-daily + fluoridated mouthwash > fluoridated dentifrice once-daily > control group. It was found that Giomer showed a greater fluoride uptake Compomer.
Keywords: Compomer, fluoride, fluoridated dentifrice, fluoridated mouthwash, Giomer
|How to cite this article:|
Dhull K S, Nandlal B. Effect of low-concentration daily topical fluoride application on fluoride release of giomer and compomer: An in vitro study. J Indian Soc Pedod Prev Dent 2011;29:39-45
|How to cite this URL:|
Dhull K S, Nandlal B. Effect of low-concentration daily topical fluoride application on fluoride release of giomer and compomer: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2011 [cited 2013 May 20];29:39-45. Available from: http://www.jisppd.com/text.asp?2011/29/1/39/79930
| Introduction|| |
Dental caries obviously still is a major problem in adults as well as in children despite the dawn of newer restorative techniques and materials. The prevalence of dental caries in children has declined markedly over the last 20 years in most countries in the Western world, but the disease continues to be a major problem for both adults and children elsewhere and needs an improved approach to prevention and therapy. 
With the advances in techniques and materials, the carious lesions can be reversed prior to cavitation by increasing the resistance of teeth to acid by encouraging the development of a remineralisation mechanism on the enamel surface. ,
There is no doubt about the fact that fluoride is one of the most useful anticariogenic agents and has a broad spectrum of mechanisms of action, which includes the formation of fluorapatite that has lower solubility than the original carbonated apatite, the enhancement of remineralisation, interference of ionic bonding during pellicle and plaque formation and the inhibition of microbial growth and metabolism. Fluoride released from restorative materials can inhibit caries through all these mechanisms, although it seems likely that the enhancement of remineralisation is the major mechanism by which fluoride released from the restorative material is effective. 
The use of fluoride to reduce the frequency of caries can be classified into preventive and restorative categories. Prevention applications include topical fluoride treatment, fluoridated dentifrice, fluoridated water and devices for controlled release of fluoride. Certain types of fluorides may also be incorporated in restorative materials, which may be beneficial because of the observed cariostatic action of fluoride. 
Pre-reacted glass ionomer (PRG) -composites (Giomers) employ the use of prereacted glass ionomer technology to form a stable phase of glass ionomer cement in the restoration. Fluoroaluminosilicate glass in these materials is reacted with polyalkenoic acid in water prior to inclusion into silica-filled urethane resin.  These materials have fluoride recharge biocompatibility, smooth surface finish, excellent esthetics and clinical stability, which has made them popular for restoration of root caries, noncarious cervical lesions, class V cavities and deciduous tooth caries. 
Polyacid-modified composite resins, known trivially as Compomers, were introduced to the profession in the early 1990s and were presented as a new class of dental material designed to combine the esthetics of traditional composite resins with the fluoride release and adhesion of glass ionomer cements.  The pattern of fluoride release from Compomer is characterized by an initial rapid release followed by rapid reduction in the rate of release after a short period of immersion. 
The decrease of fluoride release in the long term is thought to restrict the ability of materials to inhibit secondary caries around restorations because the low levels of fluoride released on the long term may not be at levels that are required for a therapeutic effect. However, it has been reported that glass ionomer cements and compomers can take up fluoride from the environment as a means of replacing fluoride that has been lost. 
However, there is lack of information about fluoride release from Giomers with continuous exposure, uptake and release from these materials.
Therefore, this study evaluated the fluoride release from Giomer and Compomer using different topical fluoride regimes over a period of 21 days.
| Materials and Methods|| |
One polyacid-modified composite resin (Compomer) and one PRG-composite (Giomer) were chosen for this study. Ninety-six specimens (48 of each material) were made by placing the restorative materials into the Teflon mold (5 mm diameter Χ 2 mm height), supported by glass slide in the mounting jig. A second glass slide was placed on top of the Teflon mold in the slot in the jig followed by tightening of the screw embedded in the vertical arms of the jig to apply gentle and uniform pressure on the upper slide to extrude the excess material.  The top surface of the Giomer and Compomer specimens were cured using a soft start polymerization unit (Translux R energy, Heraeus Kulzer Dental Division, South Bend, IN, USA), with a light exit window of 8 mm and mean intensity ≥400 mW/cm 2 according to the manufacturers' curing times.
All specimens were stored in deionised water in air tight plastic containers at 37ºC for 3 days to permit more complete setting prior to beginning the experimental phase of the study.
A pH-cycling system consisting of a demineralising solution  (CaCl 2 .2H 2 O - 2.2 mM, NaH 2 PO 4 .2H 2 O - 2.2 mM and CH 3 COOH - 0.05 M, pH adjusted with 1 M potassium hydroxide [KOH] to pH 4.4) and a remineralising solution  (CaCl 2 .2H 2 O - 1 mM, NaH 2 PO 4 .2H 2 O - 1 mM, NaCl - 35 mM, CH 3 COONa.3H 2 O - 15 mM, pH adjusted with 1 M KOH to pH 7) was used as the suspension medium for storing the individual specimens. Each specimen was stored in a 25-ml plastic container containing 10 ml demineralising solution at 37ºC for 6 h and then transferred to a new plastic container containing 10 ml remineralising solution at 37ºC for 18 h.
Test specimens were subjected to the daily fluoride exposure protocols listed in [Table 1]. Forty-eight specimens of each material were separated into four treatment groups (n = 12) as follows: (1) no fluoride treatment (control), (2) application of a 0.38% w/w sodium monofluorophosphate dentifrice (500 ppm F) for 1 min once-daily, (3) application of a 0.38% w/w sodium monofluorophosphate dentifrice (500 ppm F) for 1 min twice-daily and (4) application of a 0.38% w/w sodium monofluorophosphate dentifrice (500 ppm F) for 1 min once-daily plus immersion in a 0.05% w/v sodium fluoride mouth rinse (225 ppm F) for 1 min immediately following the first dentifrice application. Fluoride treatments were completed at the time of transfer daily for 21 days.
Media solutions were buffered with equal volumes of Total Ionic Strength Adjustment Buffer (TISAB II). This reagent matches the ionic background of standards to sample and helps to fix the ionic strength at a stable value. By matching the conductivity of both solutions, offsets in readings and measurement errors are eliminated. Fluoride content was measured using a Sartorius Professional Meter PP 25 with a "Combination" ion selective electrode.
For each restorative material/fluoride treatment combination, mean (±SD) daily fluoride release in both remineralisation and demineralisation solutions was calculated. Total daily fluoride release for each specimen was calculated by adding the amount released in the demineralising solution with that released in the remineralising solution.
Data were analyzed by repeated measures ANOVA and Tukey HSD post hoc tests (a = 0.05) to determine differences (1) within each treatment group over time and (2) among the four treatment groups during each testing period.
| Results|| |
The mean (±SD) daily fluoride release in the demineralising and remineralising solutions for each material/fluoride treatment combination are displayed in [Table 2].
|Table 2: Mean (SD±) daily fluoride release (ppm) from Giomer and Compomer |
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Repeated measures ANOVA revealed statistically significant differences in fluoride treatment effect (P < 0.0001), immersion media effect (P < 0.001) and rechargability (P < 0.001) for both the materials.
The two restorative materials demonstrated similar patterns of fluoride release over the course of the study. Fluoride release tended to be related to the dose of daily supplemental fluoride applied. For both the materials, the greatest decrease in fluoride release occurred from Day 1 to Day 3. By Day 2, the fluoride release was significantly greater in the fluoridated dentifrice twice-daily group and fluoridated dentifrice once-daily plus fluoridated mouthwash once-daily group than in the control group. Fluoride release in the fluoridated dentifrice once-daily group tended to be slightly higher than that in the control group, but lower than that in the fluoridated dentifrice twice-daily group and fluoridated dentifrice once-daily plus fluoridated mouthwash once-daily group for both the materials throughout the study [Table 2].
Immersion media played an important role in fluoride release for both the materials. Regardless of the fluoride treatment, the mean fluoride release for both the materials was significantly greater when immersed in the demineralising solution than in the remineralising solution [Table 3]. This was true even though the specimens were suspended in the remineralising solution for three times longer than in the demineralising solution.
|Table 3: Mean (SD±) fluoride release (ppm) from Giomer and Compomer in demineralising and remineralising solutions |
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| Discussion|| |
Several studies have evaluated the use of fluoride in different forms in the prevention of dental caries. As the constant presence of fluoride plays an important role in the prevention, the success of topical treatments depends on the formation of fluoride reserves capable of releasing ions for prolonged periods of time. Therefore, the fluoride recharge in restorative materials provides a potential fluoride reserve for release in an oral environment. 
The presence of trace quantities of fluoride released from the enamel is critical if the caries process is to be driven in the direction of remineralisation. Hence, the clinical effects of fluoride are strictly dependent on the methods that deliver the fluoride ion to the surface of the tooth. 
In the present study, the amount of fluoride released from Giomer and Compomer was evaluated on application of different daily topical fluoride regimes for 21 days. Giomers employ the use of prereacted glass ionomer technology to form a stable phase of glass ionomer cement in the restoration. They incorporate fillers that are produced from full or surface reaction of ion-leachable glasses with polyalkenoic acid, which are expected to release fluorides and have fluoride recharge properties, whereas in case of Compomers, fluoride release occurs subsequent to water uptake either as a result of dissolution of the glass filler particles or via the later generation of ionic reaction on the surface of the glass particles. 
In the present study, a significant difference in the mean daily fluoride release from Giomer and Compomer was observed, where the fluoride release was higher in Giomer when compared with Compomer for all the treatment groups.
Similar results were found in a study conducted by Dhull et al. (2009) and Toshiyuki et al. (2004), where the fluoride release and recharge was higher in Giomer when compared with Compomer. ,
In the present study, a pH-cycling system consisting of demineralising solution (pH 4.4) and remineralising solution (pH 7) was used as a suspension medium for storing the individual specimens, and was in accordance with the pH-cycling system described by Carvalho et al. (1999). According to Featherstone and Others (1986), this exposure mimics an in vivo high-caries challenge environment.  Each specimen was immersed in a plastic container containing 5 ml of demineralising solution for 6 h and then transferred to a new plastic container containing 5 ml of remineralising solution for 18 h.
In the present study, the amount of fluoride released was significantly higher in the demineralising solution than in the remineralising solution for all the treatment groups in Giomer as well as in Compomer.
Compared with the remineralising solution, the demineralising solution appears to have eluted significantly more fluoride from all specimens. This result occurred even though the specimens were immersed in the demineralising solution for only one-third as long as in the remineralising solution.
When exposed to an acidic challenge, both Giomer and Compomer may release additional fluoride. This may result from the dissolution of matrix-forming elements within the restorative materials. 
Other studies conducted by Freedman et al. (2003), Forss et al. (1999), Carvalho et al. (1993) and Vieira et al. (1999) have demonstrated similar fluoride release patterns. ,,,
Various methods of topical application of fluoride have been described by different authors. The rationale for the protocol followed in the present study was that most people expose their teeth to topical fluoride by brushing their teeth with a fluoride-containing toothpaste or use a fluoride-containing mouthrinse. The protocol followed in the present study differs from the protocol used by Freedman et al. with respect to the concentration of fluoride used. In the present study, fluoridated dentifrice (containing 500 ppm F) was used in the light of the development of "low" fluoride pediatric dentifrice formulations of interest to ascertain whether fluoride recharge would occur at fluoride levels less than that of most adult fluoridated toothpaste (1000-1500 ppm F). 
The present study's results suggest that increasing fluoride exposure increases fluoride uptake and release by glass ionomer-based restorative materials.
This confirms previous observations made by Forsten et al. (1991), Takahashi et al. (1993), Young et al. (1996) and Freedman et al. (2003) that glass ionomer cements can recharge after exposure to fluoride. ,,,
Freedman et al. (2003) evaluated the effect of fluoride on glass ionomer, resin-modified glass ionomer and polyacid-modified resin composites (Compomers) in a simulated high-caries environment. Thirty-two cylindrical specimens, each of a glass ionomer (Ketac-Fil), resin-modified glass ionomer (Photac-Fil) and polyacid-modified resin (Dyract AP), were created. Each specimen was subjected to one of four daily treatments (n = 8): (1) no fluoride treatment (control), (2) application of a fluoride dentifrice (1000 ppm) for 1 min once-daily, (3) application of the same dentifrice for 1 min twice-daily and (4) the same regimen as (3) plus immersion in a 0.05% sodium fluoride (NaF) mouth rinse (225 ppm) for 1 min immediately following the second dentifrice application. Each specimen was suspended in a polyethylene test tube containing 1.0 ml demineralising solution (pH 4.3) at 37ºC for 6 h and then transferred to a new test tube containing 1.0 ml remineralising solution (pH 7.0) at 37ºC for 18 h.  Fluoride treatments were completed at the time of transfer daily for 7 days. In the present study, the same methodology was followed. However, to simulate pediatric dentifrice formulation, a low-fluoridated dentifrice (500 ppm) was used.
Vieira et al. (1999) evaluated the effect of fluoride on glass ionomers and resin composite in a simulated high-caries environment. They submitted specimens of traditional glass ionomer, resin-modified glass ionomer, polyacid-modified resin and resin composite to a 14-day demineralisation/remineralisation regimen and, on Days 8-14, applied a fluoridated dentifrice (1100 ppm) to the specimens twice daily. Their results suggested that all materials were capable of absorbing fluoride from the dentifrice solution and later releasing it to the solution.  This concurs with the results of the current study.
Similarly, this study confirms the findings of Takahashi et al. (1993), who demonstrated that fluoride release by glass ionomer materials increases with exposure to increased fluoride concentration.  In the current study, the fluoride release was significantly higher in the fluoridated dentifrice twice-daily group, which received the greatest daily fluoride exposure, followed by the fluoridated dentifrice once-daily + fluoridated mouthwash group, followed by the fluoridated dentifrice once-daily group, and the control group released minimum fluoride. Although the amount of fluoride treatment given was less as compared with the study conducted by Freedman et al. (2003), the fluoride uptake was nonetheless observed in the treatment groups.
The effects of higher concentration (e.g., 5000 ppm) topical fluorides and increased numbers of daily exposures may provide additional insight into this phenomenon.
An interesting finding of the present study was the measure of the difference in fluoride release between the control group and the other treatment groups. This difference was termed as "fluoride recharge," and was significantly different for the Giomer and Compomer materials tested [Figure 1] and [Figure 2]. It is worth noting that during the first week, the fluoride recharge was almost same for both the Giomer and the Compomer groups. However, the Giomer showed greater rechargability than the Compomer in the second and third weeks. The greater rechargability of Giomer is due to the incorporation of a glass ionomer phase in the restorative material.
It is important to note that although this study was designed to mimic daily occurrences of acid challenges and fluoride exposures seen with typical home care regimens, in vitro results may not be directly representative of in vivo results. Fluoride release measured from specimens immersed in a static medium may not take into account the dynamic nature of conditions found in the oral cavity. Although the majority of fluoride release studies are designed in this manner, there are some that attempt to more closely simulate intraoral conditions.
Longer term studies are needed to evaluate the trend of fluoride release on daily topical fluoride application. Moreover, the effects of additional increases in the number and/or concentrations of daily fluoride exposures should be evaluated.
| Conclusions|| |
The following conclusions can be drawn from the study conducted:
- The fluoride release (ppm) was found to be higher in Giomer when compared with Compomer.
- The fluoride released from Giomer and Compomer was significantly greater in the acidic demineralising solution than in the neutral remineralising solution.
- It was found that increasing fluoride exposure significantly increased fluoride release from Giomer and Compomer.
- It was found that the fluoride release from the subgroups of Giomer and Compomer was in the following order: fluoridated dentifrice twice-daily > fluoridated dentifrice once-daily + fluoridated mouthwash > fluoridated dentifrice once-daily > control group.
- It was found that Giomer showed comparatively greater fluoride recharge/uptake than Compomer.
Within the limitations of this experimental design, definitive conclusions cannot be drawn and further in vivo investigations are needed to evaluate the trend of fluoride release from these materials on exposure to a daily fluoride regime under the dynamic nature of conditions found in the oral cavity.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]