|Year : 2013 | Volume
| Issue : 2 | Page : 91-95
"Effect of nano-filled surface coating agent on fluoride release from conventional glass ionomer cement: An in vitro trial"
S Tiwari1, B Nandlal2
1 Department of Paediatric and Preventive Dentistry, Peoples College of Dental Sciences, Bhopal, Madya Pradesh, India
2 Department of Paediatric and Preventive Dentistry, JSS Dental College and Hospital, Mysore, Karnataka, India
|Date of Web Publication||26-Jul-2013|
530/2F, New Dhyan Chand Colony, Sipri Bazar, Jhansi, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Context: To overcome the drawbacks of glass ionomer cement of sensitivity to initial desiccation and moisture contamination the use of surface coating agent is recommended. The search in this area led to invent of use of nanofillers in surface coating agent, but its effect on fluoride release is not clear. Aim: The aim of this study is to evaluate and compare the fluoride release from conventional glass ionomer cement with and without surface coating agent. Settings and Design: This in vitro study comprised of total 80 samples (40 samples of each with and without surface coating). Materials and Methods: Specimens were prepared, G coat plus was applied and light cured. Fluoride release of the sample was measured every 24 h for 7 days and weekly from 7th to 21 st day using Sension4 pH/ISE/MV Meter. Statistical Analysis Used: Descriptive Statistics, Repeated Measure ANOVA, Paired Sample t-test, Independent Sample t-test, Scheffe post hoc test. Results: Mean values clearly reveal a significant decrease in the fluoride release from day 1 to day 21 for both groups. Non-coated group released significantly more fluoride than surface coated group (P < 0.001). Conclusions: It can be concluded that nanofilled surface coating agent will reduce the amount of fluoride released into oral environment as compared to non-coated group and at the same time releasing fluoride into surrounding cavity walls to create zones of inhibition into the cavity floor to help internal remineralization.
Keywords: Conventional glass ionomer, fluoride release, surface coating agent
|How to cite this article:|
Tiwari S, Nandlal B. "Effect of nano-filled surface coating agent on fluoride release from conventional glass ionomer cement: An in vitro trial". J Indian Soc Pedod Prev Dent 2013;31:91-5
|How to cite this URL:|
Tiwari S, Nandlal B. "Effect of nano-filled surface coating agent on fluoride release from conventional glass ionomer cement: An in vitro trial". J Indian Soc Pedod Prev Dent [serial online] 2013 [cited 2020 Feb 24];31:91-5. Available from: http://www.jisppd.com/text.asp?2013/31/2/91/115703
| Introduction|| |
Despite the advent of newer restorative techniques and material, dental caries still remains a critical concern even today. Although, the prevalence of dental caries in children has declined markedly over the past 20 years in the western world, the disease continues to be a major problem for both adults and children elsewhere and needs an improved approach to prevention and therapy. 
Fluoride has been well-documented as a major contributing factor in the decline of the incidence and severity of dental caries. Delivery of fluoride is accomplished by several means, one of them being dental restorations, which facilitate the delivery of fluoride directly to susceptible tooth surface. Fluoride may be released from dental restorative material as a part of setting reaction or it may be added to the formulation with the specific intention of fluoride release. 
Many researchers have investigated fluoride release from various restorative materials, one among them being glass ionomer cement, which is found to reduce secondary caries initiation and propagation significantly and is well-known for its relative ease of use, chemical bonding to tooth structure, fluoride ion release, and recharge properties. It has a low coefficient of thermal expansion and has acceptable esthetic qualities.  Fluoride in glass ionomer cement does not form a significant part of the poly acid salt matrix after cement maturation. This fluoride can then be released into the oral environment without the significant corresponding loss of structural integrity.  Fluoride released from glass ionomer cement decreases cementum solubility as well as enamel solubility, and this effect occurs not only on adjacent cavity walls, but also on tooth structure not in direct contact with glass ionomer cement.  In addition, glass ionomer cement has been shown to impair the growth of cariogenic micro-organism such as streptococcus mutans in vitro as well as in vivo.  This inhibitory effect of glass ionomer cement on cariogenic microorganism, along with decreased solubility of tooth structure, underscore the value of fluoride release from glass ionomer cement.
Although, fluoride release from glass ionomer restorations has been shown to occur for long periods, the greatest fluoride release takes place in the first 24-48 h followed by a low prolonged elution. There has been found a wide variation in the reported amounts of fluoride release from dental material in previous studies, but the pattern of fluoride release remains consistent, there is high burst of fluoride release followed by a low, prolonged elution. 
However, the use of glass ionomer cement in clinics is limited due to its poor mechanical properties and sensitivity to initial desiccation and moisture. Recent developments are aimed towards overcoming some of these shortcomings. To protect glass ionomer cement from moisture contamination and dehydration during initial setting, immediate application of surface coating agent is recommended. Failure to protect the cement during initial setting allows either hydration or dehydration, resulting in crazing, cracking, early erosion, reduced physical property and translucency of glass ionomer cement. 
A variety of surface coating agents have been examined, with the council on dental material, instruments and equipments; recommending a varnish or a light activated bonding agent. Any untoward effect that a surface coating would have on long-term fluoride release would be a disadvantage and lessen the attractiveness of cement as the material of choice for caries active patients. Search in this field led to the use of nanofillers in surface coating agents to improve its wear resistance, but their effect on fluoride release is not clear.
Therefore, the aim of this study was to evaluate and compare the fluoride release from conventional glass ionomer cement with and without surface coating.
| Materials and Methods|| |
Materials used in this study were conventional Glass Ionomer Cement (GC Gold Level High Strength Posterior Restorative Material. GC Corporation Tokyo, Japan) and G coat plus-Nanofilled self-adhesive light cured protective coating (GC Corporation, Tokyo, Japan). A total of 80 specimens were taken for the study. Specimens were fabricated by placing restorative materials into the teflon mold (5 mm diameter × 2 mm height) supported by glass slide in the mounting jig. Prior to placement in the jig, Mylar strip was attached to each glass slide. A second glass slide was placed on the top of the teflon mold in the slot made 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.  After 10 min, specimens were gently demolded. G coat plus varnish was applied in surface coated group specimens. Specimens were suspended individually in 25 ml of distilled water stored at 37°C. Distilled water was renewed every 24 h for 21 days. At the predetermined measurement time each specimen was taken out of the distilled water quickly, dried with filter paper and immediately immersed in another 25 ml fresh distilled water for further equilibration.
The media solutions were buffered with 5 ml of Total Ionic Strength Adjustment Buffer 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 were eliminated. Fluoride release of the sample was measured every 24 h for 7 days and weekly from 7 th to 21 st day using Sension4 pH/ISE/MV Meter.
| Results|| |
The data were analyzed by Descriptive Statistics, Repeated Measure ANOVA, Paired Sample t-test, Independent Sample t-test and Scheffe post hoc test (α = 0.05). Mean (±SD) fluoride release (ppm) from both groups (surface coated and non-coated) is given in [Table 1] and [Table 2]. Mean values clearly reveal a significant decrease in the fluoride release from day 1 to day 21 for both groups. Results of repeated measures ANOVA revealed statistically significant difference between two groups (P < 0.001). Paired t-test revealed a significant t value on all the days (P < 0.001) except between 7 and 14 day interval (P > 0.05) for surface coated group [Table 3]. Paired t-test revealed a significant t value (P < 0.001) throughout the experimental period for non-coated group [Table 4]. The pattern of fluoride release was also different for both the groups throughout the experimental period [Graph 1][Additional file 1] and [Graph 2][Additional file 2].
|Table 1: Mean (±SD) fluoride release (ppm) from conventional glass ionomer cement from 1 day to 7 day|
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|Table 2: Mean (±SD) fluoride release (ppm) from conventional glass ionomer cement at 1, 7, 14 and 21 days|
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|Table 3: Comparison of mean changes in fluoride release (ppm) from surface coated subgroup of conventional glass ionomer from 1 day to 21 days|
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|Table 4: Comparison of mean changes in fluoride release (ppm) from non-coated subgroup of conventional glass ionomer from 1 day to 21 days|
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| Discussion|| |
To overcome the drawbacks of glass ionomer cement from moisture contamination and desiccation during initial setting stage, application of surface coating agent is recommended. In order to best protect glass ionomer cement during its critical setting stage many researchers have favored light activated resin (Mc Lean and Wilson, 1977.  Keeping this in mind, in the present study G-coat plus varnish was applied in surface coated group specimens. This material incorporates dispersion nanofiller technology, which allows a uniform dispersion of nano sized fillers to enhance the wear resistance and provides protection against acid attack. Therefore, allowing slow and steady release of fluoride for a prolonged period of time.
Various dimensions of the specimens were used in different studies. In the present study, specimens of dimensions (5 mm diameter × 2 mm height) were fabricated as explained by Freedman and Diefenderfer (2003); Dhull and Nandlal (2009). ,
Restorative material was placed into the teflon mold supported by glass slide in the mounting jig. This is to apply gentle and uniform pressure to extrude the excess material as shown in the previous studies conducted by Dhull and Nandlal (2009). 
Various methods have been described to detect fluoride release previously. Fluoride ion selective electrode is the most frequently employed technique for measurement of fluoride release Verbeeck et al. (1993), Yap et al. (2002). , In this study, fluoride release of the sample was measured using a combination ion selective electrode ISE from HACH company and Sension4 pH/ISE/MV Laboratory pH/ISE/mV Meter. This method is advantageous over others as being powerful, versatile and accurate. It is sensitive to a wide range of concentrations (10 -7 to saturated solution) and can measure fluoride in a variety of solutions. However, the cost involved is less than other methods.
In the present study, non-coated group released significantly more fluoride than surface coated group. The possible explanation for this would be without protection immature glass ionomer is quite soluble in water. In this study, application of surface coating agent led to the reduction (approx. 60%) in the release rates of fluoride from conventional glass ionomer cement.
McKnight-Hanes and Whitford evaluated the effect of varnishing on release rates of fluoride from disc made of three glass ionomer products and concluded that varnishing the disc caused a reduction of 61-76% depending upon the product. 
The pattern of fluoride release from both the groups varied. Non-coated group showed initially high fluoride release for first 2 days then declined sharply on 3 rd day and gradually diminished to a nearly constant level. Other studies by De Moor et al. (1996), Yip and Smales (2000), and Yap et al. (2002) have demonstrated similar fluoride release pattern. ,, In case of surface coated group fluoride release was gradual for 1 st week and then reduced to a consistent level for next 2 weeks. This pattern of fluoride release from surface coated groups was consistent with study by McKnight-Hanes and Whitford (1992), Castro et al. (1994), Mazzaoui et al. (2000). ,,
The results suggested that application of a surface coating agent did not completely inhibit fluoride release. However, the coating agent reduced the burst effect of fluoride release during the 1 st week and allowed for slow and steady release of fluoride.
| Conclusions|| |
It can be concluded that nanofilled surface coating agent will reduce the amount of fluoride released into oral environment and at the same time releasing fluoride into surrounding cavity walls to create zones of inhibition and into the cavity floor to help internal remineralization.
Why this paper is important to pediatric dentist:
- Glass ionomer is most widely used esthetic restorative material in pediatric dentistry but has its own drawback of sensitivity to initial desiccation and moisture
- To protect glass ionomer cement from moisture contamination and dehydration during initial setting, immediate application of surface coating agent is recommended. A variety of surface coating agents have been examined, with the council on dental material stating the lack of wear resistance of various materials, leading acid attack on glass ionomer restoration
- In the present study, G-coat plus varnish is applied on conventional glass ionomer restoration. This material incorporates dispersion nano-filler technology, which allows a uniform dispersion of nano sized fillers to enhance the wear resistance and provides protection against acid attack; thus allowing for a slow and steady release of fluoride; thus, improving the effectiveness of glass ionomer restoration to be used in pediatric dentistry.
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[Table 1], [Table 2], [Table 3], [Table 4]