## 2 Materials and Methods  
* Wave (W) [SDI, Hamilton Parkway Itasca, Australia] is a composite with a semi-fluid consistency. It contains 39.98% by weight of acrylic monomer, 60% of inorganic filler (silica), 0.01% of butylated hydroxytoluene and 0.01% of NaF. * Freedom (F) [SDI, Hamilton Parkway Itasca, Australia] contains 22% by weight of acrylic monomer, 77% of inorganic filler (strontium-fluoride glass), 0.01% of butylated hydroxytoluene and 0.10% of NaF. Samples of the tested materials were made in the shape of cylinders with a diameter of 5 mm and a thickness of 2 mm using a polyethylene matrix. The samples were fabricated with the use of the LED Elipar II lamp (3M ESPE, St Paul, MN, USA) emitting light in the wavelength range of 400-515 nm with a maximum intensity of 800 mW cm\({}^{-2}\). Curing time was 40 s. After curing, the samples were polished and cleaned of any possible residues and their contact area was calculated in mm\({}^{2}\). X-Ray Diffraction (XRD) measurements were made on the X'Pert PRO X-ray diffractometer (Cu K\(\alpha\)1, 1.5406 A) by PANalytical. The FT-IR spectra of the materials were recorded on a Thermo Scientific Nicolet iS50 FT-IR spectrometer (Waltham, MA, USA) method with DTGS/KBr detector and an Attenuated Total Reflectance (ATR) with a diamond crystal plate. The ATR-FT IR spectra were recorded between 4000 and 400 cm\({}^{-1}\) at room temperature with 4 cm\({}^{-1}\) spectral resolution. A total samples/background scans using OMNIC spectra software (Thermo Fisher Scientific Inc.) of 100 scans were accumulated for each spectrum. The Scanning Electron Microscopy (SEM) investigations were performed using a Hitachi SU-70 system (Hitachi, Chiyoda, Tokyo, Japan). Images were taken at 15 kV of accelerating voltage using detector of secondary electrons. To determine the exact amount of released fluoride ions, the ion-selective ORION (Thermo Fisher Scientific Co., Waltham, MA, USA) model 9609 electrode was used in combination with the microcomputer pH/ion meter CPI-551 Elmetron. The system was calibrated before each subsequent measurement, which was repeated three times to determine the mean value. Samples were subsequently immersed in the 5 mL of studied solutions and left without stirring in closed containers at 37 \({}^{\circ}\)C for an appropriate period of time until the determination of the released fluoride from the materials was carried out (measurements were taken after 3, 24, 48, 72, 69, and 168 h). Six samples of each material were prepared for each environment (total n = 108). After the measuring period, 5 mL of the eluate was taken for evaluation, the sample was dried and transferred to a new solution for determination (5 mL). The concentrations of fluoride released from the materials were expressed in umol/L and in relation to their surface area. The cumulative level of fluoride ion releases (i.e., total release over the whole given observation period) and the increments of releases were determined over the given measurement periods and with respect to the unit of time--1 h.  
The evaluation of fluoride release from the Wave composite material (W) and the Freedom compomer (F) was performed in 9 environments differing in composition and pH, over a period of 7 days, i.e., 168 h.  
The tested solutions consisted of artificial saliva without calcium salts at pH 4.5 (1), 5.5 (2), 6.0 (3), 7.0 (4), 7.5 (5), artificial saliva with the addition of calcium salts at pH 4.5 (6) and 5.5 (7) as well as deionized water (8) and saline solution (9). The composition of the artificial saliva was as follows [33]: NaCl (0.4 g), KCl (4.0 g), urea (1 g), Na\({}_{2}\)S \(\times\) 9H\({}_{2}\)O (0.005 g), NaH\({}_{2}\)PO\({}_{4}\)\(\times\) 2H\({}_{2}\)O, and calcium ions in the form of CaCl\({}_{2}\)\(\times\) 2H\({}_{2}\)O (0.795 g). All solutions were prepared on the basis of deionized water. To establish the correct pH values, HCl and NaOH solutions were used. All experiments were done six times and descriptive data was expressed as the mean and standard deviation (\(\pm\)SD).