# (Bio)Tribocorrosion in Dental Implants: Principles and Techniques of Investigation
## 4 Dental Implant
### Literature Overview in Dental Tribocorrosion
#### 4.2.4 The Tribocorrosion: A Multivariable Phenomenon  
Many investigations [85] tried to depict wear maps, describing them as a very useful tool to provide a reference for wear predictions in dental implants. [PERSON] et al. [86] in 2018 analyzed the trend of volume loss with load and noticed that the material loss increased in the presence of corrosion proportionally to the load applied. This can be easily demonstrated by considering the relation between load and potential as follows: the higher the load, the lower the potential and the greater the corrosion wear. As well as the former, the potential also impacts the propagation of wear, as analyzed by [PERSON] et al. in 2019 as follows [87]: for low passive conditions, the wear was low, whereas for high passive conditions it was the opposite, as expected, since the latter compromises the protection of the oxide layer. An interesting outcome is the capacity of the compacted wear debris, at open circuit conditions, of supporting the external load, reducing in this way the total wear of the coupling. Another key variable is the masticatory frequency, as analyzed by [PERSON] et al. [88] in 2019; they found that it has a relationship with oxide layer stability, understanding that the lower frequencies (1-2 Hz) allow for greater repassivation, in contrast to the higher ones at 4 Hz, where the passive film resulted in interruption. The effect is the drastic drop of potential toward negative values. The results can be easily explained by considering that, for high frequencies, the available time for repassivation is shorter and, probably, not sufficient. In reference to the dental environment, where the load and the frequencies of mastication or bruxism are variable and the loads multidirectional, these results become relevant for implant longevity. Regarding the choice of the material instead, [PERSON] et al. [1] tried, in 2021, to compare the very common grade 2 or 4 or 5 titanium implants with Zirconia Toughened Alumina and Yttria Stabilized Zirconia. The tests pointed out that the latter behaves better against wear and, therefore, can be considered a valid alternative accounting for the that titanium implants, which have the drawback of dangerous ion diffusion [89]. Another study, always in 2021 and referred to as the material choice, conducted by [PERSON] et al. [90], focalized on the ideal combination of titanium and zirconium as Ti + 5% Zr, which exhibited improved corrosion and wear resistance behavior. This does not happen for 10-15% of zirconium, where the tribocorrosion response was worst. The reason comes from the function performed by Zr as follows: it increases the hardness of the alloy, but a higher value causes microstructural changes characterized by an irregular topography, which does not permit the formation of a uniform oxide layer. Therefore, each aspect should be kept in mind when a new sample is realized. The same comparison was performed by [PERSON] et al. [91] with the following equal outcomes: the best performing were the Zr/Ti ones, i.e., zirconium for the abutment and titanium for the implant. Interesting is also the potential application of TiO\({}_{2}\) nanotubes (NTs), adopted for the improvement of osteointegration and reduction of infection released. Regarding this, [PERSON] et al., study [92] showed an enhanced tribocorrosion performance (in terms of adhesion strength and hardness) due to the growth of a nano-thick oxide film. Certainly, other particular elements [93] can also be chosen (as a coating, for example), such as niobium-based thin films, which, combined with carbon (NiC), provide optimal protective efficiency (anti-wear and anti-corrosion) and osteogenic potential (bioactivity in terms of cellular attachment, mineralization and differentiation) as stated by [PERSON] et al.