# Evaluation of the Impact of Various Functional Fillers on Key Properties of Dental Composites
## 4 Discussion
The results of the compressive strength tests revealed that the flowable composite containing 2 wt% of HAp, F, and Ag exhibited the highest compressive strength (190 MPa) among all of the tested materials. In comparison, hybrid composites with the same fillers (2 wt% of HAp, F, and Ag) tested in another study achieved an even higher compressive strength (264 MPa) [43]. Other research [50], which tested a flowable composite modified with hydroxyapatite alone, showed a compressive strength of 100 MPa. These findings suggest that the modification of hydroxyapatite with fluoride and nanosilver significantly enhanced the compressive strength of the flowable composites. The conducted bending tests revealed a decrease in the bending strength of all flowable composites. To assess the applicability of the experimental composites, the ISO 4049 Dentistry Polymer-based restorative materials 2009 standard [35] was applied, which specifies a required bending strength of at least 50 MPa. Therefore, all of the tested flowable composites met this requirement, except for the composite containing nanosilver (46.3 MPa). This difference is minimal. Among the experimental composites, the highest bending strength was observed in the variant containing 2 wt% of HAp, F, and Ag, with a value of 76.48 MPa. In terms of flexural strength, a decline in performance is observed with the inclusion of HAp compared to HAp0%, similar to the trend seen in the wear properties. Additionally, there was a noticeable trend of strength deterioration as the HAp content increased, a finding that aligns with the work of [PERSON] [51]. They suggest that the strength of composites is influenced by factors such as the type, quantity, and particle size of the material used [52; 53; 54]. To assess the durability of the material, a tribological wear test was conducted on the experimental composites. The results indicate that the type of filler used significantly influences the abrasive wear of dental composites. The lowest wear values were observed in the experimental composites containing 2 wt% hydroxyapatite, calcium fluoride, and nanosilver (1.24 \(\times\) 10\({}^{-4}\) Mm\({}^{3}\)/Nm and 5 wt% hydroxyapatite, calcium fluoride, and nanosilver (1.82 \(\times\) 10\({}^{-4}\) Mm\({}^{3}\)/Nm), compared to the control composite (3.38 \(\times\) 10\({}^{-4}\) Mm\({}^{3}\)/Nm). Similar studies on hybrid composites containing hydroxyapatite, calcium fluoride, and nanosilver also showed an improvement in tribological properties [50]. The hybrid composite with 1 wt% hydroxyapatite, calcium fluoride, and nanosilver exhibited a wear factor of 1.29 \(\times\) 10\({}^{-4}\) Mm\({}^{3}\)/Nm, which was very similar to the results observed in this study [50]. The current literature supports the idea that the morphology and particle size of the added filler can influence the tribological and mechanical properties of dental composites [8; 9; 50; 55]. Significantly higher wear was observed for the composite containing nanosilver filler (4.02 \(\times\) 10\({}^{-4}\) Mm\({}^{3}\)/Nm) compared to the other composites. This effect may be attributed to an improper polymerization process resulting from the addition of nanosilver particles as a filler. Therefore, further investigation into the interaction between nanosilver and other fillers is recommended for future studies. The conducted studies highlight the significant impact of fillers on dental compo-sites. Despite the deterioration of some mechanical properties, the obtained results are within the standards used for dental composites. The obtained results could have been influenced by the size of the filler particles and their surface properties, which allow for better bonding with the matrix. Filler crystals of different sizes can mutually fill empty spaces, which can result in the strengthening of the material.