Year : 2009 | Volume
: 27 | Issue : 1 | Page : 27--32
Comparative evaluation of fluoride release from PRG-composites and compomer on application of topical fluoride: An in-vitro study
KS Dhull, B Nandlal
Department of Pedodontics & Preventive Dentistry, JSS Dental College and Hospital, Mysore-570 015, Karnataka, India
K S Dhull
Department of Pedodontics and Preventive Dentistry, JSS Dental College and Hospital, Mysore-570015, Karnataka
Aims and Objective: To determine the fluoride release from Giomer and Compomer, using different topical fluoride regimes, and to compare the amount of fluoride release from giomer with that of compomer. Materials and Method: 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, fluoridated dentifrice (500 ppm) once daily + fluoridated mouthwash (225 ppm) group. Each specimen was suspended in demineralizing solution for six hours and remineralizing solution for 18 hours. Fluoride release was measured in both the demineralizing solution and remineralizing solution daily for seven days. Total daily fluoride release for each specimen was calculated by adding the amount released in the demineralizing solution to that released in remineralizing solution. Results and Conclusion: The fluoride release (ppm) was found to be more in Giomer when compared to Compomer. The fluoride released from Giomer and Compomer was significantly greater in the acidic demineralizing solution than in the neutral remineralizing solution. It was found that increasing fluoride exposure significantly increased fluoride release from the 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 the giomer showed a greater fluoride uptake than the compomer.
|How to cite this article:|
Dhull K S, Nandlal B. Comparative evaluation of fluoride release from PRG-composites and compomer on application of topical fluoride: An in-vitro study.J Indian Soc Pedod Prev Dent 2009;27:27-32
|How to cite this URL:|
Dhull K S, Nandlal B. Comparative evaluation of fluoride release from PRG-composites and compomer on application of topical fluoride: An in-vitro study. J Indian Soc Pedod Prev Dent [serial online] 2009 [cited 2021 May 16 ];27:27-32
Available from: https://www.jisppd.com/text.asp?2009/27/1/27/50813
Despite the advent of newer restorative techniques and materials, dental caries still remain a critical concern even today. Although the prevalence of dental caries in children has declined markedly over the last 20 years in most countries in the Western world, the disease continues to be a major problem for both adults and children elsewhere and needs an improved approach for prevention and therapy. 
One of the key factors in preventing dental caries has been recognized as increasing the resistance of teeth to acid by encouraging the development of a remineralization mechanism on the enamel surface. 
Fluoride is well documented as an anticariogenic agent. A variety of mechanisms are involved in the anticariogenic effects of fluoride, including the formation of fluorapatite that has lower solubility than the original carbonated apatite, the enhancement of remineralization, interference of ionic bonding during pellicle and plaque formation, and the inhibition of microbial growth and metabolism. 
The delivery of fluoride is accomplished by several methods, one of them is dental restoration, which facilitates the delivery of fluoride directly to the susceptible tooth surfaces.  Fluoride may be released from the dental restorative materials, as a part of the setting reaction or it may be added to the formulation with the specific intention of fluoride release.
PRG-Composites (GIOMERS) employ the use of pre-reacted 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 the 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 fluoride release and adhesion of glass-ionomer cements.  The pattern of fluoride release from a compomer is characterized by an initial rapid release followed by rapid reduction in the rate of release after a short period of immersion. 
However, there is lack of information about fluoride release from giomers, with continuous exposure, uptake, and release from these materials. 
Hence, this study evaluates the fluoride release from the giomer and compomer using different topical fluoride regimes.
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 a Teflon mold (5 mm diameter × 2 mm height), supported by a glass slide in a mounting jig. A second glass slide was placed on the top of the Teflon mold in a slot in the jig followed by the 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® energy, Heraeus Kulzer), with a light exit window of 8 mm and a mean intensity of ≥400 mW/cm 2 , according to the manufacturers' curing times.
All specimens were stored in deionized water in air tight plastic containers, at 37 0 C, for three days, to permit a more complete setting prior to beginning the experimental phase of the study.
A pH cycling system consisting of a demineralizing solution  (CaCl 2 .2H 2 O- 2.2 mM, NaH 2 PO 4 .2H 2 O - 2.2mM, and CH 3 COOH - 0.05M, pH adjusted with 1 M Potassium hydroxide (KOH) to pH 4.4) and a remineralizing solution  (CaCl 2 .2H 2 O - 1 mM, NaH 2 PO4. 2H 2 O - 1 mM, NaCl - 35 mM, CH 3 COONa.3H 2 O - 15 mM, pH adjusted with 1M Potassium hydroxide (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 demineralizing solution at 37°C for six hours, and then transferred to a new plastic container containing 10 ml remineralizing solution at 37°C for 18 hours.
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 one minute once daily; (3) application of a 0.38% w/w Sodium Monofluorophosphate dentifrice (500 ppm F) for one minute twice daily; (4) application of a 0.38% w/w Sodium Monofluorophosphate dentifrice (500 ppm F) for one minute, once daily, plus immersion in a 0.05% w/v Sodium fluoride mouth rinse (225 ppm F) for one minute, immediately following the first dentifrice application. Fluoride treatments were completed at the time of transfer daily for seven days.
The 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 & helps to fix the ionic strength at a stable value. By matching the conductivity of both solutions, offsets in readings and measurement errors were eliminated. The fluoride content was measured using the Sartorius Professional Meter PP 25 with a "Combination" ISE (Ion Selective Electrode).
For each restorative material / fluoride treatment combination, the mean (± SD) daily fluoride releases in both remineralization and demineralization solutions were calculated. The total daily fluoride release for each specimen was calculated by adding the amount released in the demineralizing solution to that released in the remineralizing solution.
Data were analyzed by repeated measures of analysis of variance (ANOVA) and Tukey HSD post hoc tests (α = 0.05), to determine the differences (1) within each treatment group over time and (2) among the four treatment groups during each testing period.
The mean (±SD) daily fluoride releases in the demineralizing and remineralizing solutions for each material / fluoride treatment combination are displayed in [Table 2].
Repeated measures of ANOVA revealed statistically significant differences in fluoride treatment effect ( p p p  As the constant presence of fluoride plays an important role in prevention, the success of topical treatment 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 oral environment. 
The phenomenon of fluoride release is a complex interaction of many factors and involves several phases. Fluoride release after topical fluoride application depends on the pH, dose, concentration, duration, and frequency of application. 
In the present study the amount of fluoride released from giomer and compomer was evaluated on the application of different daily topical fluoride regimes for seven days. Giomers employ the use of pre-reacted glass ionomer technology to form a stable phase of glass ionomer cement in the restoration. They incorporate fillers that are produced by the full or surface reaction of ion leachable glasses with polyalkenoic acid. These 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 case of the giomer, as a more extensive acid-base reaction has been carried out before blending with a resin, the hydrogel layer of the glass filler is more extensive than that in compomers. If the glass-ionomer hydrogel matrix is the key factor to control fluoride uptake and re-release, it is expected that the giomer will demonstrate more effective fluoride recharging characteristics than other resin-matrix materials. 
The present study revealed a significant difference in the mean daily fluoride release from the giomer and compomer, where the fluoride release was higher in the giomer when compared to the compomer, for all treatment groups.
In this study, a pH cycling system, consisting of a demineralizing solution (pH 4.4) and a remineralizing solution (pH 7), was used as the suspension medium for storing the individual specimens and was in accordance with the pH cycling system described by Carvalho et al . According to Featherstone and others, this exposure mimics an in vivo high caries challenge environment.  Each specimen was immersed in a plastic container containing 5 ml of demineralizing solution for six hours, and then transferred to a new plastic container containing 5 ml of remineralizing solution for 18 hours.
The amount of fluoride released is significantly higher in the demineralizing solution than in the remineralizing solution for all treatment groups of the giomer as well as compomer. Compared to the remineralizing solution, the demineralizing solution appears to have eluted significantly more fluoride from all specimens. This result occurred even though the specimens were immersed in the demineralizing solution for only one-third as long as in the remineralizing solution.
When exposed to an acidic challenge, both the 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 ., Forss et al ., Carvalho et al., and Vieira et al . 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 toothpaste containing fluoride or use a mouth rinse containing fluoride. 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 if fluoride recharge would occur at fluoride levels less than those in most adult fluoridated toothpastes (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. , Takahashi et al. , Young et al., and Freedman et al., that glass ionomer cements can recharge after exposure to fluoride. ,,,
Vieira et al . evaluated the effect of fluoride on glass ionomers and resin composites in a simulated high caries environment. They submitted specimens of traditional glass ionomers, resin-modified glass ionomers, polyacid-modified resins, and resin composites to a 14-day demineralization / remineralization regimen, and on Days 8-14, applied a fluoridated dentifrice (1100 ppm) to the specimens, twice daily. Their results suggested that all the 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 ., who demonstrated that fluoride release by glass ionomer materials increases with exposure to increased fluoride concentration.  In the current study, fluoride release was significantly greater in the fluoridated dentifrice twice daily group, which received the greatest daily fluoride exposure, followed by fluoridated dentifrice once daily plus fluoridated mouthwash group, followed by fluoridated dentifrice once daily group, and the control group released minimum fluoride. Although the amount of fluoride treatment given was less compared to the study conducted by Freedman et al .,  yet fluoride uptake was observed in the treatment groups.
The effects of higher concentration (for example, 5000 ppm) of topical fluorides and increased number of daily exposures may provide an 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 other treatment groups. This difference was termed as "fluoride recharge" and was significantly different in the giomer and compomer materials tested [[Graph 1]-[SUPPORTING:1] and [Graph 2]-[SUPPORTING:2]]. It is worth noting that the fluoride recharge was greater for giomer as compared to compomer groups.
It is important to note that although this study was designed to mimic daily occurrences of acid challenges and fluoride exposures seen with typical homecare 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.
The following conclusions can be drawn from the study conducted:
The fluoride release (ppm) was found to be more in the giomer when compared to the compomer.The fluoride released from the giomer and compomer was significantly greater in the acidic demineralizing solution than in the neutral remineralizing solution.It was found that increasing fluoride exposure significantly increased fluoride release from the 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 the 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 daily fluoride regime under the dynamic nature of conditions found in the oral cavity.
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