| Abstract|| |
Objective: The conventional methodology employed for measuring fluoride release from restorative materials is done by suspending a sample in a static media and measuring the fluoride release at designated time intervals. The main drawback of this methodology is that it does not make allowance for the dynamic system that exists in the oral cavity. Therefore a newer methodology which mimics the oral cavity by employing a continuous flow system to measure fluoride release was compared with that of the existing methodology.
Methods: Twenty disc specimens were prepared using conventional glass ionomer cement (Fuji Il, GC Co., Tokyo. Japan) and divided into two groups of ten each. In the first group fluoride release was measured using standard methodology and in the second group fluoride release was measured using a continuous flow system. In the continuous flow system. deionised water is allowed to flow through an intravenous infusion apparatus at a constant rate of 30ml/ hr stimulating the salivary flow rate. A constant volume of medium (2ml) is maintained in the drip chamber where specimen is suspended for fluoride release representing maximum volume of' saliva before swallowing.
Statistical analysis : Fluoride ion concentration from the standard and new methodology was compared using student's independent t-test.
Results: Significantly low amounts of fluoride was released from the specimens measured using the new methodology at all time intervals.
Keywords: Glass ionomer cement, fluoride ion, continuous flow system
|How to cite this article:|
Hemamalathi, Ballal S, Kandaswamy D, Gupta T. A dynamic methodology for measuring fluoride release from restorative materials. J Conserv Dent 2006;9:113-6
|How to cite this URL:|
Hemamalathi, Ballal S, Kandaswamy D, Gupta T. A dynamic methodology for measuring fluoride release from restorative materials. J Conserv Dent [serial online] 2006 [cited 2020 Aug 5];9:113-6. Available from: http://www.jcd.org.in/text.asp?2006/9/3/113/42356
| Introduction|| |
Recurrent caries remains a critical dental concern with restoration replacement accounting for 50- 70% of the dental care currently provided , . Maintaining continuous levels of fluoride in the oral environment helps to prevent demineralization and enhances remineralization of incipient carious lesions.
Fluoride releasing restorative materials have been noted to effectively inhibit the demineralization of tooth structure adjacent to restorative margins and assist in remineralization  . Many studies were conducted to evaluate the amount of fluoride release from different restorative materials. Glass ionomers have been found to release the highest amount of fluoride followed by giomers, compomers and composites ,, . Till date studies were conducted by suspending a sample in a plastic container with a specified amount of deionized water, acid solution or artificial saliva as a storage medium , . The storage medium was replaced at designated time intervals and the fluoride ion concentration was measured during the course of experiment. However, the amount of fluoride release was mostly either overestimated due to fluoride release in the same solution or underestimated due to over saturation of solution with fluoride. Thus, the amount and pattern of fluoride release from fluoride - containing restorative materials obtained from these studies do not reflect the dynamics of fluoride release in the oral environment.
The three key factors that affect fluoride release from dental materials in the oral cavity are i) composition of the material ii) manipulation of material and iii) kinetics of the oral environment. The first two factors are standardized by the manufacturer. Hence, an effort has to be made to mimic the kinetics of oral environment ie. composition and flow rate of saliva have to be considered when measuring fluoride release from restorative materials. Many studies have tried to simulate the in vivo condition by using a medium with a similar composition to that of natural saliva  . However, since saliva is secreted and swallowed constantly. the fluoride release in these in vitro studies do not mimic the characteristics of oral cavity. A lacunae still exists in studying fluoride release, as the kinetics of the salivary flow have not been properly addressed yet.
In this study, we have compared a new methodology, a "continuous flow system", which more closely mimics the kinetics of oral environment, with an already existing methodology.
| Materials and Methods|| |
Continuous flow system
An intravenous infusion pump (AKAS infu 505) was assembled and used as a continuous flow system. The plastic bottle at the top contained 500m1 of deionized water. The drip flow rate was set at 30 ml/hr during the experimental period. The drip chamber sustained 2ml of solution (deionized water). A window (6 x 6mm 2 ) was made on the side of the chamber, above the level of the solution to place the specimen into the solution and to withdraw the solution at scheduled time periods to determine the fluoride concentration. The window was sealed with water proof (PVC plumbing) tape when the experiment began.
Fluoride containing conventional glass ionomer( Fuji II, GC Co, Tokyo, Japan) was used. 20 disc specimens were prepared according to manufacturer's instructions. The mixed GIC was placed in Teflon moulds (6.0 mm in diameter and 1.5mm height). Excess cement that extruded around the edge of the mold was carefully removed with a scalpel number 15. Polyester sheets were placed on both sides of the mold, glass plates were placed over the polyester sheets and clamped to produce a smooth surface. 20 disc specimens were prepared as mentioned above and allowed to set in the mold for 15 minutes. The discs were removed from the moulds and weighed. The mean weight of each disc was 100.2mg. The discs were inspected under a magnifier (6x) to ensure that the prepared specimens were free from air bubbles and cracks.
Twenty disc specimens were divided into 2 groups (A & B) of 10 each.
Group A samples - fluoride release measured by standard (static solution) methodology
Each sample was suspended in l0 ml of deionized water in plastic containers. Storage solution was changed daily in the morning at a specific time. 2ml of solution was withdrawn from each container on 1 st and 7 th day for fluoride ion measurement. On seventh day, the disc specimens were removed from plastic containers and rinsed with l0ml of deionized water for 5 seconds. The disc was dried with a stream of air and placed in test tube containing 2% sodium fluoride mouth wash for 2 minutes. The treated disc was again rinsed with deionized water and transferred back to plastic container. 2m1 sample solution for fluoride ion concentration was again taken on 8th day
Group B samples - fluoride release measured by new methodology, "continuous flow system"
In continuous flow system, the flow rate was maintained at 30 ml/hr. One disc specimen was suspended in drip chamber containing 2ml of solution through the window and the window was sealed. The deionized water dripped into the chamber at a controlled rate. 50µm of solution in the drip chamber was transferred to 2ml plastic syringes on 1 st and 7 th day for measuring fluoride ion concentration. Immediately after withdrawal of the solution, 50µm of deionized water was added to the chamber to maintain the water volume at 2m1. The window of the drip chamber was sealed again and dripping proceeded at a controlled rate. On the 7 th day, the disc was removed from drip chamber and rinsed with 10ml of deionized water for 5 seconds. The disc was dried with a stream of air placed in a test tube containing 10ml of 2% sodium fluoride solution. The treated disc was again rinsed with deionized water and transferred back to drip chamber. 50µm of solution for fluoride ion measurement was again withdrawn on 8th day. The fluoride ion concentration from solution collected from drip chamber and plastic containers was measured using DRJ890 datalogging calorimeter by Spades method.
Fluoride ion concentration from the standard and new methodology was compared using student's independent t-test.
| Results|| |
The mean fluoride ion release from specimens from the 2 methodologies over 8 day period is presented in [Table l]. Student's independent t-test was used to calculate and compare the mean values. To confirm the significance, non parametric Mann-Whitney U-test was employed to compare the mean values. The mean fluoride release was 0.05 in the Group B specimens (continuous flow system) compared to 0.56 in the Group A specimens (standard methodology) on day 1. On day 7 the mean fluoride release was less again that is 0.02 in the Group B specimens compared to 0.16 in the Group A specimens. After recharging of the samples with 2% sodium fluoride the mean fluoride release was 0.02 in the Group B specimens and 0.47 in the Group A specimens on the 8th day. Thus the mean fluoride release from restorative materials measured using new methodology, the "continuous flow system" was significantly (P=0.0001) lower than the standard methodology at all time intervals.
| Discussion|| |
Over the past two decades a great deal of research has been carried out which has specifically addressed the property of fluoride releasing dental restorative materials to inhibit demineralization. Glass ionomer cements have been shown to release and recharge fluoride during the entire life span of the restoration , . The fluoride released has been shown to be taken up by adjacent enamel and dentin with evidence of subsequent inhibition of demineralization at tooth/restoration margin. However, the studies used to measure fluoride release from restorative materials are not similar to the kinetics of salivary flow in the oral cavity, since they store the specimen into the static storage medium for a certain length of time before fluoride level measurement. Moreover, they have attempted to simulate the clinical conditions by daily partial replacement of the storage medium  . Thus, the characteristics of fluoride release from the restorative materials in the oral cavity are not similar to those shown in conventional in-vitro studies.
Hsiu- Ming Hsu, Guay-Fen Huang et al in 2004 proposed a continuous flow system to more closely mimic the kinetics of the oral environment  . This system was designed to monitor the behavior and amount of fluoride release by placing the material in a constant flow of dissolving solution to simulate the flow of saliva across the restoration. But till date no comparative studies are available between the continuous flow system mentioned in this study and the usual static methodology employed for measuring fluoride release from restorative materials. Hence, we have done a comparative evaluation of the two systems (Standard methodology and Continuous flow system) and checked for fluoride released by Type II GIC.
Unstimulated salivary flow rates are normally 0.3 - 0.6ml/min. Therefore, we mimicked the in vivo situation with a fixed flow rate into drip chamber at 30ml/hr. The maximum volume of saliva in the mouth before swallowing was found to be 1.19ml in males and 1.07 in females  . Therefore, we kept a constant volume (2ml) of medium in the drip chamber where the specimen is suspended for fluoride releasing.
Samples were collected at 1, 7 and 8 days and fluoride release was measured using spectrophotometry. The results were statistically analysed. At day 1, the mean fluoride release was 0.05 in the "Continuous flow system" compared to 0.56 in the standard methodology. On day 7 the mean fluoride release was less again that is 0.02 in the new methodology compared to 0.16 in the standard methodology. After recharging of the samples with 2% sodium fluoride the mean fluoride release was 0.02 in the "continuous flow system" and 0.47 in the standard methodology on day 8. Thus, the mean fluoride release measured using new methodology, the "continuous flow system" was significantly lower (p= 0.0001) than the standard methodology at all time intervals. In the standard methodology, the amount of fluoride release would always be higher due to cumulative effect of fluoride released in the same medium over a time period whereas in "continuous flow system". the in vivo situation is mimicked by constant dilution and flow of solution in the drip chamber. Thus, in the oral cavity very little amount of fluoride is available for remineralization for a very short time till saliva is swallowed. Once again fluoride is released from the restoration into the new saliva secreted by salivary glands which is again swallowed. Thus, the amount of fluoride available at given point of time in the oral cavity can never equal the cumulative fluoride release measured by the static standard methodology. This is the reason for significantly low levels of fluoride being released in the "continuous flow system" as compared to the standard methodology at all time intervals.
| Conclusion|| |
To elicit the exact amount of fluoride release from restorative materials, the studies measuring fluoride release should mimic the kinetics of oral cavity where there is constant secretion and swallowing of saliva. The results of this study confirm that in conventional in vitro studies the effect of fluoride is overestimated as no allowance is made for the constant salivary dilution of the fluoride that would occur in vivo. The continuous flow system is a more realistic approach for measuring fluoride release from restorative materials. So, it can be very well called as a "Kinetic method" for measuring fluoride release.
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Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College, Chennai - 95
Source of Support: None, Conflict of Interest: None