The present study was conducted in the Department of Paediatric and Preventive Dentistry, JSS Dental College in year 2012. For the preparation of HA-GIC, Eight weight percent of the conventional glass ionomer was replaced by hydroxyapatite powder (HA) and hand mixed before addition of polyacid liquid. Total 80 specimens (40 each group) of HA-GIC were prepared for the study. Specimens were fabricated by placing restorative material (HA-GIC) into the teflon mold (5 mm diameter × 2 mm height) supported by glass slide in the mounting jig [10]. Then they were further sub divided into two groups 1- Non- Coated HA-GIC (control group), 2- Surface Coated HA-GIC.

GROUP 1 - For non coated HA-GIC (control group) prepared specimens remained uncoated. GROUP 2 - For surface coated group G coat plus coating agent was applied on specimens and light cured.

Prepared specimens were suspended individually in 25ml of distilled water and stored at 37°C in an incubator. Fluoride release of sample was measured every 24 hours for seven days and weekly from 7^th to 21^st day using combination Ion Selective Electrode (ISE) from HACH Company with Sension4 pH/ISE/MV Laboratory Meter. This equipment is more powerful, versatile, accurate and cost-effective as compare to other methods. It can measure fluoride in variety of solutions and it is sensitive to wide range of concentrations (10-7- saturated solution) [8].

Collected data was tabulated on Microsoft excel and data was analyzed using SPSS software version 17. The statistical analysis applied were descriptive statistics, Repeated Measure ANOVA, Independent Sample t-test, Paired 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/Fig-1,2]. Mean values clearly reveal a significant decrease in the fluoride release from day 1 to day 21 for both the groups. Results of repeated measures ANOVA revealed statistically significant difference between two groups (p <0.001) [Table/Fig-3].

Independent t-test revealed significant differences between two groups on all the days with t-values which are highly significant (p<0.001) [Table/Fig-4]. The pattern of fluoride release was also found to be different for both the groups throughout the experimental period [Table/Fig-1&2]. Comparison was made between mean values of surface coated HA-GIC and surface coated conventional GIC (results of our previous study [8]). In our previous study by applying Independent t-test which revealed non-significant differences between these two materials on all the days with t-values which are non significant (p>0.05) except on 14^th day where significant difference is present between two material with t-value which is significant (p <0.01) [Table/Fig-5].

Fluoride plays a major role in prevention of recurrent caries. Various fluoride releasing restorative materials have been described in the literature. Among them most widely used is GIC. This present study was designed to evaluate the effect of protective coating on fluoride release from hydroxyapatite reinforced glass ionomer, an indigenously made product (HA-GIC). In the present study this indigenous material (HA-GIC) was made by replacing eight weight percent of the glass ionomer powder by hydroxyapatite powder (particle size 5-20 microns) [9] as this proportion of hydroxyapatite led to the highest increase in flexural strength [5] and it did not impede fluoride release from this indigenous product [6,8].

Fluoride release was significantly more in non -coated group as compared to surface-coated group and non-coated group showed initial burst of fluoride release for two days then declined sharply on 3^rd day and gradually diminished to a nearly constant level. Other studies by Roeland JG et al., H K Yip et al., have demonstrated similar fluoride release pattern from different glass ionomer products [11,12]. The reason for initial burst of fluoride release from non-coated HA-GIC might be due to high solubility of immature hydroxyapatite-reinforced glass ionomer without protective coating. Fluoride release from surface coated HA-GIC was less as compared to non coated group which is consistent with our previous study on conventional glass ionomer [8] [Table/Fig-5] and also with study by C McKnight-Hanes et al., G W Castro et al., SA Mazzaoui et al., [13–15] [Table/Fig-6]. Pattern was gradual for first seven days and then decreased to constant level for next 15 days. It is hypothesized that components (metharylate) of coating agent might chemically interact with hydroxyapatite, thus influencing the fluoride release from this indigenously made product (HA-GIC). Nano-filled protective coating on HA-GIC an indigenously made product, reduced the initial burst effect of fluoride release letting on dilatory and steadfast release of fluoride for prolonged period into the oral cavity, thus helping in re-mineralization by providing more available fluoride to the cavity walls.

Invitro design is the major limitation of this study, thus further clinical investigation regarding the longevity of HA-GIC and nanofilled protective coating in the oral cavity should be carried out to authorize its use in clinical dentistry.

A perfect restorative material is clinician’s hour of need. So turning to account HA-GIC with protective coating would be a commendable choice for clinicians providing improved mechanical and fluoride releasing properties without desiccation and moisture contamination during its initial set. Also, it is aesthetic, easy to handle and bonds chemically to the tooth structure. Thus being pragmatic for primary and permanent posterior teeth, high salivary flow patients, medically and developmentally compromised patients and in places where use of composite is critical.