**4. The galvanic aspect**

**Figure 7.** Representative anodic scans from dental implants with different surface modifications. All surfaces showed a breakdown potential while MAC and DAE demonstrated a positive hysteresis in reverse scanning (a small part of re‐

**Table 4.** Ecorr, Icorr, Epit and type of hysteresis from the anodic scan curves acquired in 2% NaF+Ringer's solution. Higher

There is limited knowledge for the effect of surface roughening techniques on electrochemical properties of dental implants. OCP and anodic scans showed that sandblasting deteriorates the electrochemical properties of Ti surface, a finding that has already been reported by previous studies [30]. A speculation for this behavior is that the residual stresses developed in the subsurface during sandblasting have a detrimental effect on corrosion properties. The same trend was identified for both the Ti6Al4V and Ti6Al7Nb alloys after sandblasting in phosphatebuffered solution (PBS) [39]. However, all previous studies on ANO surfaces agreed that ANO has a positive effect on electrochemical properties. This has been tested in a variety of reagents

**Hysteresis**

**Epit (V)**

Ecorr and Epit, lower Icorr and negative hysteresis benefit the corrosion resistance.

cpTi −0.42 1.7 Without passive region Negative MAC −0.47 46.2 Without passive region Positive TPS −0.69 19.1 0.20 Negative DAE −0.72 4.0 0.18 Positive SLA −0.68 83.8 Without passive region Negative ANO −0.56 1.8 1.32 Negative

verse scanning curve at 2 V is appeared for all materials).

**Icorr (μA/cm2 )**

**Ecorr (V)**

162 Dental Implantology and Biomaterial

Galvanic coupling can be easily developed in the oral cavity between dental implants and implant-retained superstructures especially under peri-implantitis conditions. Concerning the galvanic couple of Ti with dental alloys, a few studies have been conducted employing different reagents. **Tables 5**, **6** and **7** illustrate potential differences of various galvanic couples between Ti and dental alloys. The values are sorted in descending order from the highest positive value towards the lower negative value. In most cases, the precious alloys show positive values implying that Ti will be under anodic control. In this scenario if the galvanic corrosion is triggered, then the alloy under cathodic control (precious alloys) remains immune while Ti will be dissolved. In contrast Ti is in cathodic control with all base Co–Cr and Ni–Cr alloys which means that Ti will be protected while the base alloys will be corroded under the galvanic action [21]. Given that galvanic action is triggered when the difference in potential is above 0.2 V the couples with minimal difference to Ti is ideal to avoid galvanic action and corrosion of one of the two alloys. As implant-retained superstructures are replaced easier than implants themselves, it is recommended that dental implants should be under minimal cathodic control.


**Table 5.** Difference in potential between Ti and dental alloys in modified artificial saliva with pH 7.2 [20].

However, all previous values used smoothly machined or polished Ti surfaces which achieved great difference in OCP values with treated root surfaces (**Figures 4** and **6**). DAE have almost 0.2 V difference with MAC surface which can be representative of collar. This means that the exposure of DAE surface and collar to Ringer's solution is close to galvanic threshold. Differences with MAC surface (collar) is even higher in the case of 2% NaF+Ringer's solution denoting that galvanic corrosion is still possible between collar and root of the implant itself in some cases. Of course, the presence of superstructure facilitates the galvanic phenomena more. However there is limited knowledge on this matter and definitely further research is required in this topic while the development of guidelines for clinicians to minimize intraoral corrosion of dental implants might have a beneficial effect on longevity of implant-retained restorations.


**Table 6.** Difference in potential between Ti and dental alloys in artificial saliva at 37°C [12].


**Table 7.** Difference in potential between Ti and dental alloys in Fusayama reagent with pH 5 at 37°C [21].

## **5. Conclusions**

