*4.3. HA Film Coating on Titanium by SPT to Develop an Osteoconductive Porous-Surfaced Dental Implant Body*

A HA film coating was achieved when Ti-AT was soaked in calcium phosphate solution at 37 ◦C for seven days and at 60 ◦C for one day (Figures 6 and 7).

In a 37 ◦C immersion treatment, a HA film coating was achieved when polished-Ti and Ti-AT were soaked in calcium phosphate solution for seven days. The approximate size of the precipitated HA spherical particles on Ti-AT was 40–50 μm. In a 60 ◦C immersion treatment, an HA film coating was achieved when the Polished-Ti and Ti-AT were soaked in the calcium phosphate solution for 24 h. The approximate size of the precipitated HA spherical particles on Polished-Ti was more than 40 μm, and was 20 μm on Ti-AT.

These results suggest that the size of the HA spherical particles precipitated during the immersion treatments in the calcium phosphate solution was too large to coat the titanium implant with a porous surface structure. Furthermore, in the 37 ◦C immersion, there was less precipitation compared to the 60 ◦C immersion. For a dense precipitation of HA, the temperature must be 60 ◦C or more. Temperature of the mineralizing solution must be 37 ◦C during the initializing of the solution plasma treatment.

With 5 M NaOH treatment and subsequent SPT in the calcium phosphate solution, dense nucleation with critical size nuclei was successfully precipitated on the sample (Figure 12c) and a thin and dense HA layer consisting of fine spherical crystals was formed on the titanium disk surface after SPT for 30 min (Figure 3b).

The solution plasma surface modification for coating HA onto titanium proceeds in a wet process unlike other HA surface methods using a dry process. Therefore, the coating of a HA film consisting of fine crystals on the entire surface of titanium implant bodies with porous surface structures can be achieved. MC3T3E1 cells were observed not only on the outer surface, but also on the surface of the concavity (Figure 10), indicating that the induction of bone tissue on the entire porous surface would occur successfully and that bone tissue ingrowth could be expected. To enhance the growth of mineralized tissue into the pore spaces and to keep the vascular system interconnected by the pores for continued bone development, the porous structure of a titanium implant provides a unique biological bone anchorage to the titanium implants. Enhancement of bone/implant mechanical bonding can allow dentists to use dental implant bodies with a short length, which can greatly contribute to an increase in the ability of dental implants to be used for a wide variety of treatment options, especially for patients with low bone quality and with advanced maxillary/mandibular residual ridge resorption.
