|Year : 2013 | Volume
| Issue : 4 | Page : 234-239
Comparative evaluation of fluoride release and recharge of pre-reacted glass ionomer composite and nano-ionomeric glass ionomer with daily fluoride exposure: An in vitro study
Jayanthi Mungara, John Philip, Elizabeth Joseph, Sakthivel Rajendran, Arun Elangovan, Girija Selvaraju
Departments of Pedodontics and Preventive Dentistry, Uthandi, Chennai, Tamil Nadu, India
|Date of Web Publication||21-Nov-2013|
Department of Pedodontics and Preventive Dentistry, 2/102, East coast road, Uthandi, Chennai-600 119, Tamil Nadu
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aim: This in vitro study was designed to investigate the effects of daily fluoride exposures on fluoride release and recharge by prereacted glass ionomer (PRG) composite and nano-ionomeric glass ionomer. Materials and Methods: Seventy-two specimens (36 of each material) were prepared and by placing the restorative materials into Teflon mold. Each specimen was subjected to one of three daily treatments (n = 12): (1) No fluoride treatment (control); (2) application of a fluoride dentifrice (1,000 ppm) once daily; and (3) the same regimen as (2), plus immersion in a 0.05% sodium fluoride (NaF) mouth rinse (225 ppm) immediately following the dentifrice application. Specimens were suspended in a storage vial containing 10 ml demineralizing solution for 6 h and transferred to a new test tube containing 10 ml remineralizing solution for 18 h. Fluoride treatments of the specimens were completed every day prior to their immersion in the demineralizing solution. Media solutions were buffered with equal volumes of total ionic strength adjustment buffer (TISAB) II; fluoride levels were measured using a digital ion analyzer and fluoride electrode throughout the 21 day duration of the experiment. Results: Nano-ionomeric glass ionomer showed a better amount of fluoride release than PRG composite irrespective of the fluoride treatment supplementation (P < 0.01). Additional fluoride supplementation improved fluoride release and recharge ability for both the materials when compared to their respective control groups. The fluoride recharge for both materials did not show any sustained pattern of release. Conclusion: Nano-ionomeric glass ionomer demonstrated a greater ability to release and recharge compared with that of PRG composite.
Keywords: Fluoride recharge, fluoride release, nano-ionomeric glass ionomer, pre-reacted glass ionomer composite
|How to cite this article:|
Mungara J, Philip J, Joseph E, Rajendran S, Elangovan A, Selvaraju G. Comparative evaluation of fluoride release and recharge of pre-reacted glass ionomer composite and nano-ionomeric glass ionomer with daily fluoride exposure: An in vitro study. J Indian Soc Pedod Prev Dent 2013;31:234-9
|How to cite this URL:|
Mungara J, Philip J, Joseph E, Rajendran S, Elangovan A, Selvaraju G. Comparative evaluation of fluoride release and recharge of pre-reacted glass ionomer composite and nano-ionomeric glass ionomer with daily fluoride exposure: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2013 [cited 2019 Jul 24];31:234-9. Available from: http://www.jisppd.com/text.asp?2013/31/4/234/121820
| Introduction|| |
Dental caries is a microbial disease of the calcified tissues of the teeth. It is still considered to be one of the most prevalent chronic diseases affecting the human race.  The progression or reversal of the caries process depends on the balance between pathological and protective factors. Fluoride has been identified as one of the protective factors, which tilts the caries balance towards the positive side. The use of fluoride to reduce the frequency of caries can be divided into preventive and restorative categories. Several restorative materials like glass ionomer cements, resin modified glass ionomer cements, compomers, and giomers have received attention due to their adhesive nature, improved physical and chemical properties, and their ability to release and recharge fluoride.
Fluoride containing dental materials show clear differences in the fluoride release and uptake characteristics and may act as fluoride reservoir to increase fluoride level in saliva, plaque, and hard dental tissues; and may help to prevent or reduce secondary caries. , Short- and long-term fluoride release from restorative materials are related to their matrices, setting mechanism, fluoride content, nature of fluoride incorporated into resin-based materials, and also depends on several environmental conditions. ,
There is a great variance in fluoride release among different types of glass ionomer cements probably due to the differences in composition, powder/liquid ratio, and mixing time.  Research in the development of fluoride containing materials to improve the physical properties of these materials and to provide long-term fluoride release has led to the development of the nano-ionomeric glass ionomer. This new material intends to bring adequate mechanical properties, to enhance esthetics in terms of smoothness, and polishability and precision of shade characterization.
A recent addition to the continuum of hybrid restorative materials is the prereacted glass ionomer composite (PRG-composite/giomer). Manufacturers claim that the beneficial effects of glass ionomer cements are retained along with the superior physical and esthetic properties of resin composite materials. 
The ability of a restorative to act as a fluoride reservoir is mainly dependent on the type and permeability of filling material, on the frequency of fluoride exposure, and on the kind and concentration of the fluoridating agent. 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 PRG composite can take up fluoride from the environments as a means of replacing fluoride that has been lost.  The source of fluoride for replacement can either originate from daily low concentration sources like fluoride dentrifices and fluoride mouth rinses or it can also be taken up from the oral fluids at very low concentrations.
Bearing these facts in mind, the present study was undertaken with an aim to evaluate the fluoride release and recharge of PRG composite (Beautifil II, Shofu Inc.) and nano-ionomeric glass ionomer (Ketac N100, 3M ESPE) with daily fluoride application.
| Materials and Methods|| |
The present in vitro study was conducted by the Department of Pedodontics and Preventive Dentistry, Ragas Dental College and Hospital, Chennai in association with the Department of Safety Engineering, Indira Gandhi Center for Atomic Research, Kalpakkam.
Seventy-two specimens (36 of each material) were prepared and cured as per the manufacturers' recommendations by placing the restorative materials into a Teflon mold (5 mm × 2 mm). Each specimen was subjected to one of three daily treatments (n = 12): (1) No fluoride treatment (control); (2) application of a fluoride dentifrice (1,000 ppm) for 1 min once daily; (3) the same regimen as (2), plus immersion in a 0.05% sodium fluoride (NaF) mouth rinse (225 ppm) for 1 min immediately following the dentifrice application. Each specimen was suspended in a storage vial containing 10 ml demineralizing solution (pH 4.4) at 37°C for 6 h, then transferred to a new test tube containing 10 ml remineralizing solution (pH 7.0) at 37°C for 18 h. Fluoride treatments of the specimens were completed every day, prior to their immersion in the demineralizing solution. Immersion media solutions were buffered with equal volumes of total ionic strength adjustment buffer (TISAB) II; it is used to decomplex fluoride and provide a constant background ionic strength. Fluoride levels were measured using a digital ion analyzer and fluoride electrode. Fluoride release was measured throughout the 21 day duration of the experiment.
| Results|| |
The data from the experimental procedure was tabulated and statistically analyzed. Statistical analysis was done using repeated measures analysis of variance (ANOVA), one-way ANOVA, followed by post hoc Tukey's test, and unpaired t-test. A P-value of <0.05 was considered to be significant.
[Table 1] shows the comparative evaluation of fluoride release from PRG and nano-ionomeric glass ionomer into demineralizing and remineralizing solutions at weekly intervals for a period of 21 days with daily fluoride supplements. Immersion media played an important role in the amount of fluoride released for both the materials. There was a statistically significant difference between the amount of fluoride released into the demineralizing and remineralizing solutions (P = 0.000**) for both the restorative materials, with more amount of fluoride being released into the demineralizing solution for all the fluoride treatment groups. On comparing the amount of fluoride released over a period of time, repeated measures ANOVA showed significant differences in fluoride release between days 1, 7, 14, and 21 (P = 0.000**) for both materials in demineralizing and remineralizing solutions for all fluoride treatment protocols.
|Table 1: Comparative evaluation of fl uoride release from prereacted glass ionomer and nano-ionomeric glass ionomer into demineralizing and remineralizing solutions at weekly intervals for a period of 21 days with daily fl uoride supplements|
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[Table 2] shows the comparison of mean fluoride release (mean ± standard deviation (SD)) between PRG composite and nano-ionomeric glass ionomer on days 1, 7, 14, and 21. There was a significantly higher amount of fluoride release from nano-ionomeric glass ionomer as compared with PRG composite, irrespective of the fluoride treatment protocol throughout the study period (P = 0.000**).
|Table 2: Comparison of fl uoride release (mean±standard deviation (SD)) (ppm) between prereacted glass ionomer composite and nanoionomeric glass ionomer (days 1, 7, 14, and 21)|
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[Table 3] shows the recharging ability of PRG composite and nano-ionomeric glass ionomer. The recharge ability was calculated as the difference in the fluoride release between treatment groups and the control group. No sustained pattern of recharge was shown in both the groups but nano-ionomeric glass ionomer better recharge ability compared to PRG composite.
|Table 3: Daily fl uoride recharge (mean±standard deviation (SD)) (ppm) of prereacted glass ionomer composite and nano-ionomeric glass ionomer|
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| Discussion|| |
Fluoride is a well-documented anticariogenic agent  and the release of fluoride from dental restorative materials is assumed to inhibit caries formation, progression, and secondary caries initiation through a variety of mechanisms like reducing the acidogenecity of plaque, thereby not favoring the growth of Streptococcus mutans.  Fluoride release is dependent on various factors. Since the fluoride levels leached from fluoride containing materials decrease over time, recharging of the restoratives with fluoride has been suggested to maintain a continuously increased level of fluoride release. The ability of a restorative material to act as a fluoride reservoir is mainly dependent on the type and permeability of filling material, on the frequency of fluoride exposure and on the kind and concentration of the fluoridating agent. , Bearing these facts in mind, the present study was undertaken to evaluate the fluoride release and recharge of PRG composite and nano-ionomeric glass ionomer which are relatively recent additions to the field of pediatric restorative dentistry.
PRG composites employ the use of PRG technology to form a stable phase of glass ionomer cement.  Manufacturers claim that the beneficial effects of glass ionomer cements are retained along with the superior physical and esthetic properties of resin composite materials. 
In 2007, a new generation of resin modified glass ionomer cement was introduced (Ketac Nano) described by the manufacturers as nano-ionomer with improved physical properties. The indications for the use of nano-ionomeric glass ionomer are Class I, II, III, and V restorations, interim therapeutic restorations for primary teeth and small Class I, III, and V restorations, transitional restorations, "sandwich" (stratification beneath bonded resin-based composite (RBC)) technique in permanent teeth. 
All the restorative specimens to be evaluated were mixed following the manufacturer's instructions and fabricated using a standardized procedure. They were then stored in deionized water for 3 days to complete the setting reaction. The protocol for topical fluoride application was in accordance to Freedman and Diefendefer, which was based on the rationale that most people exposed their teeth to topical fluoride by brushing with fluoride containing toothpaste or using fluoride containing mouth rinse.  Fluoride release of glass ionomers might also be increased when application of the fluoridated dentifrice is performed by brushing of the samples instead of storage of the samples in dentifrice slurries.  The specimens were exposed to pH cycling system which was proposed by Carvalho and Cury  and a fluoride ion selective electrode was used for finding the fluoride release. Fluoride ion selective electrode is well-documented and an accepted procedure. ,
Fluoride release was greater in demineralization solution when compared to the release in the remineralization solution (P = 0.000**) for both the PRG composite and nano-ionomeric glass ionomer irrespective of treatment protocol throughout the study period, even though the specimens were immersed in the demineralizing solution for only one-third as long as in the remineralizing solution. The increasing amount of fluoride in acidic media could be explained by the fact that a decrease in pH increases the dissolution of the material leading to a higher fluoride level in the acidic immersion. ,
Another explanation for the higher fluoride release in acidic media is that fluoride is principally used as a flux in the manufacturing process and is incorporated into the glass component. Upon mixing the glass powder with polyalkenoic acid, the fluoride ions are released by the initial attack on the surface of the glass particles. Fluoride is not a matrix-forming species and takes no further part in the setting reaction, but remains within the matrix. 
There was an initial high release during the first 2 days which was then followed by a rapid reduction in the rate of release of fluoride till day 7 followed by a gradual reduction till day 21 for both the materials in either of the solutions irrespective of treatment protocols. This initial rapid release of fluoride on the first 2 days is termed as "fluoride burst." , This is in contrast to the findings of Yap et al., who found no initial fluoride burst effect with prereacted glass ionomeric composite. 
Fluoride release after application of fluoridated agents may occur partly by washout of fluoride ions that are retained on the surface or in the pores of the restorative. Surface bound fluoride might be more easily detached during an acidic attack, such as in erosion. Also, free fluoride incorporated into the matrix might be washed out.  Glass-ionomers are mostly found to have significantly better capability to act as a fluoride reservoir than composite resin-based materials. This fact can be explained by the loosely bound water and the presence of solutes in the porosities in the glass ionomer, which may be exchanged with an external medium by passive diffusion.  The absorption and re-release of fluoride might be determined by the permeability of the material. Thus, a completely permeable substance could absorb the ions deep into its bulk; while a relatively impermeable material can only absorb fluoride into the immediate subsurface. 
There was also a significant difference in the amount of mean fluoride release between nano-ionomeric glass ionomer and PRG composite with higher fluoride release from nano-ionomeric glass ionomer (P = 0.000**) compared to the PRG composite irrespective of the treatment protocol throughout the study period [Table 2]. The difference can be possibly explained as the nano-ionomeric glass ionomer contains nanosized filler particles, which provide a larger surface area, thereby increasing the acid-base reactivity, and hence, has the capacity to release fluoride from the powder more quickly, increasing the fluoride release of the material. 
In the present study, there was a significant difference in the amount of fluoride released with respect to increase in the fluoride supplementation compared to control group throughout the experimental period [Table 3]. With respect to PRG composite, similar findings were reported by Dhull and Nandalal  and by Itota et al.  Also, no sustained pattern of recharge was noticed among both the materials. Nano-ionomeric glass ionomer showed significantly higher amount of fluoride recharge than PRG composite except for days 4-6. In general, materials with higher initial fluoride release have higher recharge capability.  The daily exposure of filling materials to fluoridated dentifrices has demonstrated a high rechargability for glass ionomers, while resin-based materials have demonstrated a negligibly small amount of replenishment.  The present study is an attempt to find out the fluoride release and recharge from two recent restorative materials claimed by the manufacturers to have superior physical and chemical properties with higher fluoride releasing capacity and wide range of application in pediatric restorative dentistry.
| Conclusion|| |
Within the limitations of the present study, it can be concluded that nano-ionomeric glass ionomer showed better fluoride release and recharge with higher amount of fluoride release into demineralizing solution than remineralizing solution. Also fluoride supplementation increases the uptake and release of fluoride ions of the study materials. The fluoride releasing capacity decreases over a period of time. Future studies should be aimed towards controlled clinical trials with more complex experimental designs comprising of large number of factors which influence the properties of dental materials in real clinical situations to draw valid conclusions.
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[Table 1], [Table 2], [Table 3]