# Micro-Raman Spectroscopy of Dental Implants Subjected to Different Surface Treatments
## 4 Discussion  
This study evaluated qualitatively, by means of RS, the TiO\({}_{2}\) layer on dental implants made of Ti-6 Al-4V subjected to the most common surface treatments performed during the production procedures. The analysis showed an increase of the thickness of amorphous TiO\({}_{2}\) in the following steps in ascending order: N1, N3, N2, N4, N4A, and N5. LPP did not affect TiO\({}_{2}\) presence and quality, except for on the N4A surface, which showed an increased oxide layer relative to the untreated surface. Our observations indicate that the increase in the complexity of the surface treatment corresponds to an increase in the thickness of the surface oxide layer, but the formation of crystalline TiO\({}_{2}\) has not been observed. N1, N3 and N2 surfaces showed a low Raman intensity even though it progressively increased, corresponding to a reduced TiO\({}_{2}\) thickness. This result is compatible with that of a study carried out on commercially available implants, in which the constitutive alloy is not reported [36]. N1 showed the lowest Raman intensity; this result should not be interpreted as the absence of an oxide layer, but as the presence of a thinner oxide layer than the analysis capacity of RS can detect, of the order of 10 nm, as already reported in the literature [12]. For the N2 surface, the RS peak at about 416 cm\({}^{-1}\) is interpreted as the presence of Al\({}_{2}\)O\({}_{3}\), as also reported on commercially available implants [36]. As the RS signal of corundum traces is present on all the Al\({}_{2}\)O\({}_{3}\)-blasted surfaces, it is possible to affirm that the treatments of acid etching, anodization and cold plasma evaluated in this study were not able to completely remove the corundum residues. Surface N4 showed a further increase in RS intensity but did not indicate the presence of crystalline TiO\({}_{2}\). Instead, a previous study showed for an Al\({}_{2}\)O\({}_{3}\)-blasted and double acid-etched surface a much higher RS intensity and a spectrum clearly corresponding to the presence of crystalline TiO\({}_{2}\)[36]. However, it must be considered that the two surfaces are very different both in the type of acid treatment and in the composition of the titanium bulk. These results would seem to indicate that the combined treatment of sandblasting and acid etching assessed in the present study on grade five titanium alloy is not able to stimulate the growth of crystalline TiO\({}_{2}\), as was previously reported using different acids and etching times on commercial pure grade four titanium. The N5 surface showed the greatest RS intensity, without indicating the presence of crystalline TiO\({}_{2}\). Previously published results regarding commercially available implants with an anodized surface instead showed instead in the spectrum clearly indicative of a significant presence of anatase [36]. Additionally, in this case, it should be pointed out that the two surfaces were very different both for the anodizing treatment and for the bulk material. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **N1** & **N5** & **N5A** \\ \hline
**Ti** & 85,6 & 66,7 & 68,2 \\
**O** & 1,6 & 18,7 & 17,8 \\
**Al** & 5,8 & 7,5 & 7,3 \\
**C** & 4,1 & 4,8 & 4,2 \\
**V** & 2,9 & 2,6 & 2,6 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Elemental composition of N1, N5, N5A samples as derived from EDS analyses. The data are expressed as percentage of weight (wt%). Previously, it has been reported that anodization treatment produces the formation of anatase also on grade five titanium [34]. In that study, however, the anodizing treatment occurs with a lower current (20 V instead of 60 V) and for much longer times (15 min instead of 15 s). Other studies showed the formation of anatase on grade four titanium implants subjected to anodizing processes [37]. Additionally, in this case, besides the anodizing process being different, the material constituting the bulk was also different.