**3. Electrochemical properties**

**Sa [26] Sa [27] Ra [24]**

**Table 2.** Sa (average roughness over the complete 3D surface) and Ra (average roughness along X or Y axes) values for

Implant surfaces are further differentiated in elemental composition as appeared by EDX analysis (**Figure 3**). All spectra showed C and N which should be appended to surface contamination while O should be attributed to surface oxide film. For SLA, Na and Cl were also identified and might be appended to residues of NaCl solution where the implant is placed to avoid atmospheric contamination. P in ANO has been retained from the solution used

Although Ti oxide is spontaneously formed when Ti is exposed to atmospheric oxygen, a recent study employing Raman analysis illustrated great differences among the oxide type developed on different surfaces [28]. According to the results of this study, MAC surface contains mainly

**Figure 3.** X-ray EDS spectra from the root surface of dental implants prepared by different surface roughening techni‐ ques. All surfaces illustrated the presence of Ti while C and N should be appended to surface contamination. The pres‐ ence of O is involved with oxide film. Na and Cl were also identified for SLA and might be appended to residues of NaCl solution where the implant is stored. P in ANO has been retained from the solution used during anodization.

Collar 0–0.4

DAE 0.9 0.5

ANO 1.7 2.0

collar and root regions of implants from dental literature.

during anodization.

158 Dental Implantology and Biomaterial

MAC 0.9 0.5 0.2 TPS 5.2 7.0

SLA 2.6 1.6 1.2

All the surfaces show an almost steady open circuit potential (OCP) in Ringer's (**Figure 4**), indicating a rapid establishment of equilibrium between surface and solution. The OCP values range from −0.28 up to −0.05 V while cpTi showed −0.05 V close to previous reported values [29]. OCP curves illustrate that the potential of all surfaces is quickly stabilized. MAC and TPS showed values close to cpTi while SLA and ANO showed slightly lower OCP values. A few peaks at ANO curve might be appended to reactions taking place at the surface craters. However this is only a speculation and it needs further experimental verification. DAE showed the lowest OCP value. All the treated surfaces showed lower OCP values compared to cpTi a finding which has been also detected for sandblasting compared to reference Ti surface [30].

**Figure 4.** Open circuit potential (OCP) curves in Ringer's solution. All implants show an almost steady curve over the time, indicating a rapid establishment of equilibrium between surface and solution. The ionization tendency is in‐ creased towards lower OCP values.

**Figure 5** illustrates representative anodic scan curves along with a small part of reverse scanning while the electrochemical data are presented in **Table 3**. SLA and TPS demonstrate a few oxidation peaks (pointed by the black arrows) while all curves show negative hysteresis implying that the oxide film can be reformed after an unexpected breakdown. Similar Ecorr values have been reported in dental literature (−0.35 V [31], −0.4 V [32] and −0.18 V [29]). However, all Ecorr values of treated surfaces moved cathodically denoting an increase tendency of surface to react. All surfaces show a passivation region and Epit of cpTi was found close to previously reported values (0.45 V [32]. ANO showed the highest Epit (**Table 3**) compared to others.

**Figure 5.** Anodic scans from dental implants with different surface modifications. Oxidation peaks (pointed by black arrows) were identified for TPS and SLA. All the surfaces showed a breakdown potential (Epit) and negative hysteresis in reverse scanning (a small part of reverse scanning curve at 2 V is appeared for all materials).


**Table 3.** Ecorr, Icorr, Epit and type of hysteresis from the anodic scan curves obtained in Ringer's solution. Higher Ecorr and Epit, lower Icorr and negative hysteresis benefit the corrosion resistance.

values have been reported in dental literature (−0.35 V [31], −0.4 V [32] and −0.18 V [29]). However, all Ecorr values of treated surfaces moved cathodically denoting an increase tendency of surface to react. All surfaces show a passivation region and Epit of cpTi was found close to previously reported values (0.45 V [32]. ANO showed the highest Epit (**Table 3**) compared to

**Figure 5.** Anodic scans from dental implants with different surface modifications. Oxidation peaks (pointed by black arrows) were identified for TPS and SLA. All the surfaces showed a breakdown potential (Epit) and negative hysteresis

**Table 3.** Ecorr, Icorr, Epit and type of hysteresis from the anodic scan curves obtained in Ringer's solution. Higher Ecorr and

**Epit (V)** **Hysteresis**

in reverse scanning (a small part of reverse scanning curve at 2 V is appeared for all materials).

cpTi −0.27 3.8 0.22 Negative MAC −0.84 3.6 0.55 Negative TPS −0.52 20.3 0.43 Negative DAE −0.79 7.4 0.29 Negative SLA −0.62 39.4 0.04 Negative ANO −0.68 3.4 1.26 Negative

**Icorr (μA/cm2 )**

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

**Ecorr (V)**

others.

160 Dental Implantology and Biomaterial

**Figure 6.** OCP curves in 2% NaF+Ringer's solution. ANO showed an increase in OCP values compared to Ringer's sol‐ ution. However, the OCP values of the rest implants moved cathodically although potential is again quickly stabilized as in the original Ringer's solution.

Many researchers have focused on the effect of fluoride ions on the corrosion resistance of dental implants as many dental products such as toothpastes, mouthwashes, prophylactics gels and others are proposed for the oral hygiene of patients with dental implants. However, Ti oxide is very vulnerable to fluoride ions and thus the corrosion resistance of dental implants is seriously compromised [33–35]. Generally, in F<sup>−</sup> containing media the surface of Ti showed a strongly bound complex Na2TiF6 followed by a huge increase in surface roughness [36]. However, the presence of F<sup>−</sup> reduces the corrosion resistance of dental alloys too [37]. In Ringer's solution with 2% NaF all OCP curves moved cathodically in a range from −0.4 to −0.2 V. Previous studies reported that OCP of cpTi in Ringer's solution is ranged between −0.08 [29] and 0.05 V [38], implying that the surface roughening techniques applied have moved the OCP cathodically. Surprisingly, ANO showed an increase in OCP in the 2% NaF+Ringer's solution, while the OCP of the rest implants moved cathodically due to the more aggressive nature of this reagent. However, the potential is again quickly stabilized as in the original Ringer's solution.

Similar to Ringer's solution the anodic scan curves showed that surface roughening techniques move Ecorr value to lower values while passive region was vanished for cpTi, MAC and SLA. In addition, DAE and MAC showed positive hysteresis denoting that in the case of oxide breakdown the reformation of the oxide film is impossible under these conditions (**Figure 7**). Again ANO showed the best corrosion resistance properties demonstrating the highest (1.32 V) Epit value (**Table 4**).

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


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

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 including PBS and media with cells simulating inflammatory conditions [17], Ringer's [40], PBS [41] and 0.9% NaCl [42]. Interestingly the same findings were found for Ti6Al4V and Ti6Al7Nb [42]. Recent data showed that no correlation was identified between roughness parameters and electrochemical properties in both the aforementioned solutions meaning that surface roughness cannot affect the corrosion resistance and thus the electrochemical proper‐ ties are not dependent on how rough the surface is [26].
