Objective: The aim of this study was to determine the effect of two adhesive systems and a glass ionomer coating resin on the amount of released fluoride ions from different restorative materials over a period of 168 days. Additionally, pH changes in the immersion medium were monitored. Null hypotheses were made that there is no statistically significant difference between the tested dental materials in the amount of released fluoride ions, mass changes, and changes in pH of immersed medium and that there is no difference between released fluoride ions in materials prepared with or without dentin adhesive systems/coatings. Regarding the time factor, the null hypothesis was set that there were no statistically significant differences in the stated parameters between individual time points. Material and methods: Four different restorative materials were investigated: a giomer Beautifil II (Shofu Dental GmbH, Ratingen, Germany), an “alkasite” material Cention (Ivoclar Vivadent, Schaan, Liechtenstein), a conventional composite Filtek Z250 (3M Deutschland GmbH, Neuss, Germany), used as a negative control, and a conventional glass ionomer cement Fuji IX Extra (GC, Tokyo, Japan), used as a positive control. Light-cured composite specimens were coated using two adhesive systems: a universal adhesive G-aenial Bond (GC Europe, Leuven, Belgium) and a universal fluoride-releasing adhesive Clearfil Universal Bond Quick (Kuraray Europe, Hattersheim am Main, Germany). The glass ionomer cement specimens were coated using GC Fuji Coat LC (GC Europe, Leuven, Belgium). Uncoated specimens were used as references. Specimens of the composite materials were prepared using cylindrical Teflon molds of 6 mm in diameter and 2 mm in height. The molds were placed on a polyethylene terephthalate (PET) foil, filled with uncured material and covered with another layer of PET foil (15). The excess material was removed, and specimens were polymerized using an LED curing unit (Bluephase G2, Ivoclar Vivadent, Schaan, Liechtenstein) with a nominal intensity of 1200 mW/cm2 for 20 s on each side. Specimens of the GIC were cast into the mold described above, covered with PET films, and left Katarina Kelić, disertacija_________________________________________________________________ to set for 6 min, as per manufacturer’s instructions (16). To ensure that the specimens were surrounded by an aqueous medium, a plastic thread incorporated within each specimen was used to hang the specimens from the cap of the vial. A plastic thread was weighed before incorporation in order to calculate exact sample mass. Samples were weighed at every time interval using analytical balance ABS-N/ABJ-NM (KERN, Balingen, Germany). Each sample was immersed separately into a plastic vial containing 5 ml of deionized water at 37 °C and evaluated after 0, 1, 2, 7, 28, 84, and 168 days. At each time interval, the specimens were removed from the aqueous medium, placed in 5 ml of new deionized water and stored in the incubator until the next time point. The pH of the medium, in which the specimens were stored, was first measured using the pH meter MP 220 (Mettler Toledo, Columbus, Ohio) and the InLab Expert Pro pH electrode (Mettler Toledo, Columbus, Ohio). Prior to the pH measurement, the electrode was calibrated using standard buffer solutions at pH = 4 and pH = 7. A volume of 4.5 ml of the medium and 0.5 ml of TISAB III buffer (Total Ionic Strenght Adjustment Buffer, Thermo Fisher Scientific, Chelmsford, USA) were placed in a new beaker to determine the concentration of fluoride ions. Quantitative fluoride ions release was measured using a standard ion-selective electrode Orion 9609BNWP (Thermo Fisher Scientific, Massachusetts, USA), ISO 19448: 2018. Before measurements, the ion-selective electrode was calibrated using a series of standards of known concentration in a range of 10−5 –10−2 mol/L F− . Results: The cumulative amounts of fluoride ions released after 168 days increased for the uncoated specimens of the restorative materials in the following order: Filtek Z250 < Beautifil II < Cention < Fuji IX Extra. When comparing cumulative values after 168 days, FUJ demonstrated 3 times higher values than CN, and 35 times higher values than BF. FIL released fluoride ions only when fluoride-releasing adhesive CB was applied. The composite specimens coated with Clearfil Universal Bond Quick released a lower amount of fluoride ions than the uncoated specimens, with cumulative values reached after 168 days increasing in the following order: Filtek Z250 < Beautifil II < Cention. The composite specimens coated with G-aenial Bond also released lower amounts of fluoride ions compared to the uncoated specimens; with cumulative values increasing in the following order: Filtek Z250 < Beautifil II < Cention. pH values among dental materials differed in the first measurement (1 h time point) in the following order: FIL < FUJ < CN < BF (6,16, 6,47, 6,83, and 7,26). Also, the values differed at the last measurement (168 days): FUJ < FIL < CN < Katarina Kelić, disertacija_________________________________________________________________ BF (6,56, 6,63, 6,91, and 7,45). pH values showed growth tendency over time in all tested materials. The composite specimens coated with G-aenial Bond in all groups showed pH values in the acidic range (4,4- 5,7) at time intervals of 1 hour and 24 hours. There was no statistical significance in mass changes in all tested materials. Conclusion: The amount of released fluoride ions varied among dental materials and depended on the use of adhesive systems and coatings. The glass ionomer Fuji IX Extra showed the highest values of released fluoride ions followed by the alkasite material Cention and the giomer Beautifil II. Both adhesive systems and the coat had a diminishing effect on released fluoride ions. pH values of the immersion medium differed among materials, treatments, and time points. The amount of released fluoride ions showed a growth tendency over time in all tested materials. pH values showed growth tendency over time in all tested materials. The lowest pH values were identified in all material specimens when coated with G-aenial Bond. Immersion in deionized water didn´t show statistical significance in mass changes in all tested materials during all time points.