## 4 Discussion  
In recent years, the use of fluoride-releasing materials for core build-ups and cavity restorations has increased considerably. There are several hybrid restorative materials on the market, such as bioactive resin composites, compomers, gomers, and resin-modified glass ionomers. In order to maintain the therapeutic benefits of conventional glass ionomers and composite resins, hybrid materials have been developed to solve the problems of these other materials [24]. The present study was performed to evaluate the effect of radiotherapy in a therapeutic dose (70 Gy over 35 cycles per 2 Gy/day) on the fluoride release from seven modern restorative dental materials. All the fluoride ion-releasing materials in this study showed a sustained release of fluoride ions, as reported in several previous studies. [PERSON] et al. were able to release fluoride ions from SIC and showed the long-term release of fluoride ions; the values differed among the materials, which the authors explained by the composition of the material and mixing method [25]. In their study, [PERSON] et al. reported the release of fluoride ions from SIC for up to 2 years [26]. The caries-inhibiting effect of fluoride has led to the increasing use of fluoride-releasing restorative materials [27], while various laboratory studies have also been conducted to evaluate the degree of fluoride release from the substances [28; 29; 30]. According to reports, the increased fluoride release from GICs could have a stronger antimicrobial effect [31]. The type of material, chemical composition, powder-to-liquid ratio used in material preparation, mixing technique, surface area of the material exposed to the environment, storage medium, pH of the environment or storage medium, surface treatment, and finishing procedures are some of the variables that affect the fluoride release from restorative materials [32]. Ionizing radiation could be among these elements. In general, the changes in various restorative materials caused by radiotherapy are the result of a combination of \"destructive\" processes, e.g., breaking of chains by high energy [33] or \"constructive\" processes and improvements in the degree of transformation and cross-linking [34], which are also caused by high-energy photons. It is possible that this can lead to change in fluoride release, but we cannot exclude the possible combined output of these two things, which have opposite effects on material properties. Since only the combined net effect can be measured experimentally, it is difficult to separate the relative contribution of the \"destructive\" and \"constructive\" processes, and it is almost impossible to predict which of the two processes will dominate in a given material without empirical testing. The recommended radiotherapy protocol for head and neck cancer increased the amount of released fluoride using Activa Presto, where a higher release of fluoride was recorded in the experimental group on the first day of irradiation (\(p<0.001\)), while on the other days, a higher release was recorded in the control group, as well as with Luminos and Beautiful II. With Fuji Triage and Fuji IX, the release of fluoride was higher in the experimental group compared to the control group, while with Equia Forte HT, there was no difference between the groups. With Cention Forte, there was no significant difference in fluoride release between the experimental and control groups. Therefore, the null hypothesis, that there is no significant effect of ionizing radiation on the fluoride release in tested restorative materials, was partially rejected. Unfortunately, studies on the release of fluoride ions under the influence of ionizing radiation are lacking; therefore, we could not compare our results to other studies, but we used data from the literature in general on the release of fluoride ions in restorative materials to compare with our findings.