## 4 Discussion
It was also suggested that because the hydroxyl group mediates protein binding in adsorption to the titanium surface [16], while hydrophilicity was acquired through removal of carbohydrates in the S-100 group, in the UV group, photofunctionalization not only degraded carbohydrates, but also introduced the hydroxyl group into the surface, resulting in a higher amount of adsorption than that in the S-100 group. On the cell adhesion test, the cell attachment area was significantly larger in the UV group than in the Control and S-100 groups at fresh and in the S-100 and UV groups than in the Control group at 4 weeks. It has been reported that cell adhesion decreases on the surface with aging-associated hydrophobicity and influences the subsequent cell response and contributes to proliferation and differentiation of osteoblasts [16; 17]. In our study, carbon adhered to and decreased the surface energy in the Control group and changes in the surface electrical potential made cells unable to readily adhereto the titanium surface, whereas many cells adhered in the S-100 and UV groups, which may have been because of an increase in the surface energy due to removal of carbon and changes in the surface electrical potential. On rhodamine-phalloidin staining, the cellular skeleton was thin and a space was present between cells in the Control group, whereas the cellular skeleton was thick and cells densely proliferated in the S-100 group and cells were more densely present in the UV group. On the cell proliferation test, the value was significantly higher in the S-100 and UV groups than in the Control group at 24 h and significantly higher in the UV group than in the Control and S-100 groups at 72 h. On the basis of the fact that surface hydrophilicity contributes to early cell adhesion [17], the value may have been high in the S-100 and UV groups to which hydrophilicity was added at 24 h, and the value was higher in the UV group with superhydrophilicity at 72 h.  
On the animal experiment, BIC was significantly higher in the S-100 group than in the Control group. It has been reported that hydrophilicity of the titanium surface is involved in adsorption of various proteins and cytokines influencing osseointegration and cell adhesion, decreasing BIC [18; 19; 20; 21], which may have been associated with the higher BIC value in the hydrophilic S-100 group than that in the hydrophobic Control group. Active new bone formation was observed around the Ti disk in the S-100 group compared with that in the Control group. To acquire sufficient osseointegration of implant surface, appropriate bone quality, fixture microstructure, and bone bioactivity are important [22; 23; 24; 25]. In this study, mirror-polished titanium discs were placed in insufficient areas of cancellous bone. Thus, the BIC of the S-100 treatment was twice as high as the control--its value was about 40%. However, if micro rough surface titanium disks were used, the BIC will be further increased. In addition, it have been reported that UV treated titanium surface showed significantly higher BIC in vivo study [3; 21]. In this in vitro study, UV treatment showed significantly higher bioactivity than the S-100 treatment. Even though UV treated disks were used for in vivo study, the BIC of UV treated disk was considered to be significantly higher than the S-100 treatment. Furthermore, given the reduction in the number of animals, UV treated titanium disks were not used in this in vivo study. For implant surface treatment, installment of special equipment in a disinfection room of the dental clinic is necessary [26]. The results of the in vitro tests clarified that surface activity almost equivalent to that acquired by photofunctionalization was acquired by short-time S-100 treatment. In addition, the in vivo test shows that biological aging improves and promotes new bone formation. These results suggest that this treatment method functionalizes the Ti surface at chair-side easily at a low cost with space-saving.