Journal of Indian Society of Pedodontics and Preventive Dentistry
Journal of Indian Society of Pedodontics and Preventive Dentistry
                                                   Official journal of the Indian Society of Pedodontics and Preventive Dentistry                           
Year : 2012  |  Volume : 30  |  Issue : 4  |  Page : 284--287

Comparative evaluation of fluoride release from hydroxyapatite incorporated and conventional glass ionomer cement: An in vitro study


S Tiwari1, B Nandlal2,  
1 Department of Pedodontics and Preventive Dentistry, Peoples College of Dental Sciences, Bhopal, India
2 Department of Pedodontics and Preventive Dentistry, JSS Dental College, Mysore, India

Correspondence Address:
S Tiwari
Department of Pedodontics and Preventive Dentistry, Peoples College of Dental Sciences, Bhopal
India

Abstract

Background: Glass ionomers are most commonly used esthetic restorative material, but has inferior mechanical properties. The search to improve its mechanical properties led to the use of hydroxyapatite (HA) whiskers as strengthening material for glass ionomer cement but its effect on fluoride release is still not clear. Aims: To evaluate and compare the fluoride release from HA incorporated glass ionomer and conventional glass ionomer cement (CGIC). Settings and Design: This in vitro study comprised of total forty sample. Twenty Specimens of each HA incorporated glass ionomer and conventional glass ionomer were fabricated. Materials and Methods: Specimens were suspended individually in 25 mL of distilled water in a 50 mL plastic container and stored at 37°C. Distilled water was renewed every 24 h for 21 days. Fluoride release of sample was measured every 24 h for 7 days and weekly from 7 th day to 21 st day using Sension4 pH/ion selective electrode/mV meter. Statistical Analysis Used: Descriptive statistics, Repeated Measure analysis of variance, Paired Sample t-test, Independent Sample t-test, scheffe post hoc test. Results and Conclusion: There was a significant decrease in the mean fluoride release from day 1 to day 21 for both the groups hydroxyapatite glass ionomer cement and conventional glass ionomer cement ([HA-GIC] and CGIC). Though, the mean values of HA-GIC were slightly lower than C GIC, there was no statistically significant difference in the mean fluoride release between HA-GIC and CGIC throughout the experimental period. Within the limitations of this experimental design, definitive conclusions cannot be drawn and further investigations at a molecular level are needed to evaluate the trend of fluoride release from this material.



How to cite this article:
Tiwari S, Nandlal B. Comparative evaluation of fluoride release from hydroxyapatite incorporated and conventional glass ionomer cement: An in vitro study.J Indian Soc Pedod Prev Dent 2012;30:284-287


How to cite this URL:
Tiwari S, Nandlal B. Comparative evaluation of fluoride release from hydroxyapatite incorporated and conventional glass ionomer cement: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2012 [cited 2020 Sep 19 ];30:284-287
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Full Text

 Introduction



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. [1]

Many researchers have investigated the fluoride release from various restorative material, 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. [2]

However, the use of glass ionomer cement in clinics is limited due to its poor mechanical properties and sensitivity to initial desiccation and moisture. [3] Recent developments are aimed towards overcoming some of these shortcomings. Some of them being Atraumatic Restorative Technique, Resin modified glass ionomer cement, incorporation of silicon carbide whiskers into glass ionomer cement (GIC) but all of them have their own draw backs. [4],[5] The search for a biologically compatible and potentially glass ionomer adhering material led to the use of hydroxyapatite (HA) whiskers as strengthening material for glass ionomer cement. [6]

HA has excellent biological behavior and its composition and crystal structure is same as apatite in human dental structures and skeletal system. Glass ionomer have found to interact with HA via carboxylate group. [7]

It has been proved from various studies that addition of HA into glass ionomer cement, regardless of form, improves its mechanical properties [8] but its effect on fluoride release is still not clear.

Therefore, this study evaluates and compares the fluoride release from HA incorporated hydroxyapatite glass ionomer cement (HA-GIC) and conventional glass ionomer cement (CGIC).

 Materials and Methods



HA incorporated glass ionomer and conventional glass ionomer were chosen for this study. Before conducting this in vitro study clearance from the institutional ethical committee was obtained and the material used in this study were non hazardous. 40 Specimens (20 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. [9]

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 an 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 sample was measured every 24 h for 7 days and weekly from the 7 th day to 21 st day using Sension4 pH/ion selective electrode/mV meter.

 Results



The data were analyzed by repeated measures of analysis of variance (ANOVA) scheffe post hoc tests (α =0.05). Mean (± SD) fluoride release in parts per million (ppm) from both (HA-GIC and CGIC) 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. Results of repeated measures ANOVA revealed statistically non-significant difference between two restorative material (P > 0.05) The mean values of fluoride release decreased from day 1 to day 21 significantly for both (HA-GIC and CGIC). Paired t-test revealed a significant t-value (P < 0.001) [Table 3] and [Table 4].{Table 1}{Table 2}{Table 3}{Table 4}

The two restorative materials demonstrated similar patterns of fluoride release throughout the experimental period. Both HA-GIC and CGIC showed initially a high fluoride release for first two days then declined sharply on 3 rd day and gradually diminished to a nearly constant level.

 Discussion



HA powder has been incorporated into glass ionomer cement at different weight percentages (8%, 19% and 25%) by many researchers. In the present study, eight weight percent of the powder was replaced by HA powder (particle size 5-20 microns) as this proportion of HA led to the highest increase in flexural strength as was shown in the initial investigation by Lucas et al. [2]

In the present study, 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 et al. [9],[10]

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 (Yap et al.; Verbeek et al. [11],[12] In this study fluoride release of sample was measured using a combination 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 wide range of concentrations (10 -7 to saturated solution) and can measure fluoride in variety of solutions. Furthermore, the cost involved is less than other methods.

In the present study, both HA-GIC and CGIC, showed initially a high fluoride release for first two days then declined sharply on 3 rd day and gradually diminished to a nearly constant level.

Other studies by Lucas et al., AUJ Yap et al., and Verbeeck et al., Roeland et al., Yip et al., have demonstrated similar fluoride release pattern. [2],[11],[12],[13],[14]

The pattern of fluoride release from HA-GIC and CGIC in this study was in agreement with Tay and Braden, who explained that it occurred possibly because two processes have been involved. The first process is characterized by initial short term burst of fluoride release from the surface, after which the elution was markedly reduced. This first process is accompanied by second bulk diffusion process in which small amounts of fluoride ions continue to be released into the surrounding medium for periods of 2 years to 5 years. [15]

In the present study, no statistically significant difference (P > 0.05) was found in the fluoride release between HA-GIC and CGIC, though HA-GIC showed a slight decrease in fluoride release during the experimental period. The added HA does not contain any fluoride ions so the fluoride release must have originated entirely from fluoride containing aluminosilicate glass. It is diffusion through this matrix, or decomplexation of the fluoride in the poly salt matrix which determines the long term fluoride release. [16]

The similar results were found in the study conducted by Lucas et al. They reported that conventional glass ionomer and HA incorporated glass ionomer exhibited a similar pattern of fluoride ion elution. The highest elution was recorded for both during the first 24 h and gradually decreased until 91 st day. There was no significant difference in the fluoride release between two groups throughout the study period.

It is assumed that since GIC powder is replaced by HA, therefore, the reduced fluoride content of new HA-GIC powder will lead to decrease in the fluoride release. Furthermore, it is hypothesized that complexing of fluoride with HA will cause a reduction in the fluoride release. These could be the possible explanations for a slight decrease in the fluoride release from HA-GIC during the experimental period.

 Conclusion



There was a significant decrease in the mean fluoride release from day 1 to day 21 for both the groups (HA-GIC and CGIC).Though, the mean values of HA-GIC were slightly lower than CGIC, there was no statistically significant difference in the mean fluoride release between HA-GIC and CGIC throughout the experimental period.

Within the limitations of this experimental design, definitive conclusions cannot be drawn and further investigations at the molecular level are needed to evaluate the trend of fluoride release from this material.

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