A Teflon mold was used for samples preparation. The mold was sandwiched between two glass plates to allow setting of glass ionomer under pressure. Capsules of Ketac Fil were activated likewise then triturated according to manufacturer instructions for 15 s, injected in the holes of the mold in one increment. The mold was filled to slight excess, the specimen’s top surface was covered by a Mylar strip and a glass slide was secured to flatten the surface and pressed with standard load 500 mg over the mold then left for setting. Capsules of both photac Fil and F2000 were triturated according to manufacturer instructions for 15 s and injected into holes, covered with glass slide, and light cured for 40 s per each side using a light source (Pencure, J Morita MFG corp., Japan).

Each disk specimen was removed from the mold by separating its two halves and placed in a numerated plastic tube containing 5 ml of distilled water, tightly sealed with a cap. The specimens were incubated at 37��C during the whole experimental period (3 months). After 24 h, samples were divided into three groups (30 samples per each). Each group represents a type of glass ionomer used. Each group was further subdivided into three sub-groups, 10 samples for each group. The first sub group was a control group, the second sub group was bleached with Opalescence Xtra (OX), and the last one was bleached with Opalescence Quick (OQ). Second and third subgroups were bleached with the two bleaching agents OX and OQ according to their manufacturer instructions, every sample was covered with 2 ml of the bleaching material and left for 1 h.

Disks were then washed thoroughly with distilled water, and then returned back to their tubes. Control samples (the first sub group) returned back to the tubes after water in the tubes of all subgroups being changed with new 5 ml of distilled water. The measurements were performed after 1 week, 1 month, and 3 months and every time, samples were rinsed with distilled water and water in the tubes changed with new 5 ml of distilled water. Fluoride release measurements were performed using specific ion electrode (PH meter F-22 ��HORIBA��) after adding total ionic strength adjustment buffer (TISAB) solution. The amount of fluoride released from the three tested materials was expressed in ppm.

Statistical analysis Data were recorded and analyzed by using one-way Analysis Of Variance (ANOVA) Batimastat followed by Bonferroni multiple comparison post hoc test at the significance level of �� =0.05. The analysis of variance was carried out considering the factors (material, time, and interaction). RESULTS Time had highly significant effect on fluoride released from all glass ionomer materials under test at P < 0.05 [Table 1]. Ketac Fil showed initial burst in fluoride release in the first week (T1) of 58.6 ppm, then concentration of fluoride decreased sharply after 1 month (T2) of 10.94 ppm.