## 4 Discussion  
It is considered that the implant surface properties affect behaviors of cells and proteins necessary to acquire osseointegration, and biological aging of titanium has been clarified to decrease protein adsorption and cell adhesion to the Ti surface [1; 4; 13]. On this basis, surface modification, such as photofunctionalization, is performed and the implant surface made hydrophobic by biological aging is cleaned and returned to hydrophilic [5]. Recently, commercial implants have been given an original surface morphology of each company, and in some products, fixture is stored in saline to block exposure to the air to prevent biological aging [10]. Although this photofunctionalization may be effective to prevent biological aging of titanium, there are several problems, such as the fact that the UV is expensive dedicated equipment and long operation times are necessary. Thus, we designed and evaluated a new treatment method capable of modifying the surface easily within a short time using no special equipment even in a general dental clinic. S-100(r) used in this study is special functional water containing abundant OH\({}^{-}\) ions [12], which detach/clean off adhering substances by inducing an electrical repulsion force between the adhering substances and matrix. We considered that the surface can be cleaned and modified utilizing this action. Regarding the aging of titanium, it has been clarified that trace elements in the air, such as carbon, adhere to the titanium surface and decrease the surface polarity, and the surface becomes hydrophobic as the surface energy decreases [3; 9]. The percentage of carbon differed between the Control and S-100 groups on trace element analysis, suggesting that acquisition of hydrophilicity by treatment with S-100(r) was associated with removal of carbon and the increase in oxygen was the result of exposure of the titanium oxide layer of the titanium surface by removal of carbon. The titanium implant surface is hydrophilic and having polarity immediately after processing and adhesion protein can bind to it directly or via Ca\({}^{2+}\)[3; 13], but polarity is lost as carbohydrates in the air adhere to the titanium surface and the contact angle increases to 60\({}^{\circ}\) or greater, with which the surface becomes hydrophobic and protein adsorption decreases. When photofunctionalization was applied to the surface, the contact angle decreased to below 5\({}^{\circ}\), being superhydrophobic [3]. In our study, the results of contact angle measurement performed as evaluation of hydrophilicity clarified that S-100 treatment decreased the contact angle and the surface was changed from hydrophobic to hydrophilic. However, the S-100 treatment could not improve superhydrophilicity such as the UV treatment. This may have been because of the fact that introduction of the hydroxyl groups to the titanium surface by the photocatalytic effect was combined in the principle of acquisition of superhydrophilicity by photofunctionalization, in addition to degradation of carbohydrates by reactive oxygen [14; 15]. However, in our preliminary experiment in which the sandblasted surface was treated with S-100(r), the contact angle decreased to below 5\({}^{\circ}\), acquiring superhydrophilicity. On the protein adsorption test, a significant difference was noted between fresh and 4 weeks in the Control group, clarifying that protein adsorption decreased as a result of aging-associated hydrophobicity of the surface at 4 weeks compared with that at fresh. In addition, no significant difference was noted between the Control and S-100 groups at fresh, but the surface changed to hydrophobic in the Control group at 4 weeks after progression of aging and the amount of protein adsorption was higher in the S-100 and UV groups with a hydrophilic surface.