**5. Conclusions**

The present study demonstrated that it is possible to acquire a homogenous precipitation of hydroxyapatite over the entire surface of a smooth and porous titanium disk by the implementation of a solution plasma surface modification treatment in a mineralizing solution. The solution plasma-treated samples showed significantly better cyto-compatibility than the other specimens.

**Author Contributions:** Conceptualization K.E.; Methodology, K.E. and T.S.; Software, A.B.D. and M.R.H.; Validation, F.N.-T. and T.N.; Formal Analysis, A.B.D., T.N. and F.N.-T.; Investigation, A.B.D.; Resources, K.E.; Data Curation, A.B.D.; Writing-Original Draft Preparation, K.E. and A.B.D.; Writing-Review & Editing, T.S. and M.R.H.; Visualization, A.B.D. and M.R.H.; Supervision, K.E. and T.N.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to acknowledge the Division of Orthodontics and Dentofacial Orthopedics, School of Dentistry, Health Sciences University of Hokkaido for their technical support.

**Conflicts of Interest:** The authors declare no conflict of interest.
