## 3 Results
### Results of Contact Angle Measurements and Surface Free Energy Calculation  
The median data of water and diidomethane (DIM) test liquids' contact angles with range on polished and sandblasted SDR, TECBF, and TEC surfaces are summarized in Figure 4.  
The water contact angles were 66.88\({}^{\circ}\), 79.01\({}^{\circ}\), and 72.93\({}^{\circ}\) for polished SDR, TECBF, and TEC, respectively. On the sandblasted composite surface, the water contact angles were 77.17\({}^{\circ}\), 81.59\({}^{\circ}\), and 81.04\({}^{\circ}\) for SDR, TECBF, and TEC, respectively. The representative  
Figure 4: Box plot diagram of water and diiodomethane (DIM) contact angles on polished (PO) and sandblasted (SB) SDR, TECBF, and TEC surfaces (\({}^{\bullet}\)_p_ < 0.05). Figure 3: Scanning electron microscopy (SEM) micrographs from polished and sandblasted SDR, TECBF, and TEC composite surfaces. water contact angle pictures on polished and sandblasted SDR, TECBF, and TEC surfaces are shown in Figure 5.  
Statistically, on the polished composite surface, the SDR significantly differed from TECBF and TEC (\(p<0.05\)). Furthermore, the TECBF and TEC also significantly differed from each other in terms of water wettability. On sandblasted surfaces, the SDR repeatedly differed significantly from TECBF and TEC (\(p<0.05\)), but the sandblasted TEC and TECBF presented similar wettability properties against water (\(p=0.085\)). The lowest water contact angle was shown at the SDR polished surface, and the highest one was at the TECBF sandblasted surface. This relatively high water contact angle indicated that the water behaved as a bad wetting liquid on the composite surface, resulting in rather hydrophobic surfaces of the tested composite. The DIM contact angles were \(38.32^{\circ}\), \(34.09^{\circ}\), and \(35.15^{\circ}\) on polished SDR, TECBF, and TEC surfaces, respectively. The DIM contact angles were \(29.11^{\circ}\), \(26.27^{\circ}\), and \(29.39^{\circ}\) on sandblasted SDR, TECBF, and TEC surfaces, respectively. The representative DIM contact angles were \(38.32^{\circ}\), \(34.09^{\circ}\), and \(35.15^{\circ}\) on TEC surfaces, respectively. The  
Figure 5: Representative images of water drops on polished and sandblasted SDR, TECBF, and TEC surfaces indicating the left (L) and right (R) contact angles. angle pictures on polished and sandblasted SDR, TECBF, and TEC surfaces are shown in Figure 6.  
Statistical analysis revealed that the SDR differed significantly from TECBF and TEC (\(p<0.05\)) on polished surfaces. On the sandblasted surface, the SDR significantly differed from TECBF, and TECBF significantly differed from TEC in terms of DIM contact angle. The TECBF presented the lowest DIM contact angle both on polished and sandblasted surfaces. The low DIM contact angle indicated that the non-polar DIM test liquid behaved as a good wetting liquid on composite surfaces. To examine the effect of surface treatment, it was found that the water contact angle significantly increased, and the DIM contact angle significantly decreased due to the sandblasting at all three composites. Moreover, the DIM had significantly better wettability on composite surfaces than polar water liquid (\(p<0.05\))  
Overall, the water and DIM contact angle analysis expressed that RBC surfaces had a hydrophobic nature because of the relatively high polar liquid and low apolar liquid contact angle measurements. The water drops behaved differently on SDR, and this bulk-fill composite was more wettable for water than TECBF and TEC. The DIM wettability also  
Figure 6: Representative images of diidomethane (DIM) drops on polished and sandblasted SDR, TECBF, and TEC surfaces indicating the left (L) and right (R) contact angles. showed differences between the composite. Its wettability was lower on the SDR surface than TECBF and TEC. For DIM, the TECBF and TEC surface was more wettable than SDR.