## 2 Materials and Methods  
Highly porous HA was obtained from aragonitic cuttlefish (_Sepia officinalis_) bone from the Adriatic Sea by using the hydrothermal method. The HA powder in the form of hexagonal column crystal aggregates with a diameter of \(<\)180 m was prepared by grounding and sifting bones through a 180 m size sieve [20]. In the present study, two GICs were used: Fuji II LC and Fuji IX GP Extra (GC Corporation, Tokyo, Japan). The HA powder 2, 5, and 10 wt % (three experimental groups) and a glass powder were hand-mixed using a mortar and pestle for 20 min to obtain a homogenous powder. The prepared powder was then mixed with the polyacrylic acid by spatula. Four groups were prepared for each GIC material; the first group was without HA particles, while in the powder of three experimental groups 2, 5, and 10 wt % HA respectively was added. For microhardness and SR testing sectional Teflon holds (5 mm diameter \(\times\) 2 mm deep) were used to prepare 10 samples per group (n = 80). After mixing the GIC components by spatulation, the material was poured into a syringe (Centrix, Shelton, CT, USA) and immediately into Teflon molds. To avoid air trapping, polyester strips were placed and the material was gently compressed on both sides of the mold by glass. Fuji IX specimens were left to set for one hour. Both sides of each Fuji II sample were light-cured for 20 s to ensure a proper setting, using a LED lamp (Ivocalr Vivadent AG, Schaan, Lichtenstein, Germany), with intensity 600 mW/cm \({}^{2}\). The specimens were stored in distilled water at 37 \({}^{\circ}\)C for 7 days and than tested. SR and microhardness measurements were conducted on the same sample. SR was measured using a contact type profilometer device (Perthometer M2, Mahr GmbH, Gottingen, Germany). Multidirectional readings were made for each specimen in five different areas. After five sequential measurements were performed at different locations for each specimen, the arithmetic mean of SR was calculated in m. Specimens were fixed with a special jig to ensure that their position is the same for all measurements. Microhardness measurements were performed using a digital microhardness tester (HMV-2, Shimadzu Corp., Kyoto, Japan). A 980 N force was applied to the specimens with a diamond indenter for 15 s. The testing machine was calibrated before each measurement. Indentations were made after the specimen surfaces were divided into four quadrants. Two measurements were taken in each quadrant, totaling eight measurements. The mean of the eight measurements represented specimen mean. These points were not at the margins or areas with visible irregularity. Microhardness was expressed as Vickers hardness number (VHN). One specimen from each group was sputter-coated with gold and observed under SEM (JSM-6400 SEM, JEOL, Tokyo, Japan) at magnifications X15, X50, and X100. Samples for the FR measurements were prepared as described for microhardness and SR. Six discs (8 mm diameter \(\times\) 2 mm thick) for each GIC group were made using a Teflon mold (n = 48). After setting of material, samples were removed from the molds by applying pressure at one side and individually stored in polyethylene vials, in 5 mL deionized water and left at 37 \({}^{\circ}\)C for 24 h. The concentrations of fluoride released into the water were measured after 24 h, 7 days, and 45 days in triplicate for each sample and expressed in mg/L (ppm F\({}^{-}\)). The deionized water was replaced after every testing procedure. For the measurements, each disk was removed from the water, dried on filter paper, weighed, and immediately immersed in 5 mL fresh deionized water for further measurements. The fluoride concentrations in the water samples were measured using an Ionoselective electrode (F800 DIN, Xylem Analytics Germany, Weilheim, Germany) connected to an ion analyzer (inoLab Multi 9630 DS; Xylem Analytics Germany, Weilheim, Germany).