# (Bio)Tribocorrosion in Dental Implants: Principles and Techniques of Investigation
## 4 Dental Implant
### Literature Overview in Dental Tribocorrosion
#### 4.2.2 The Influence of the Solution Chemical Composition  
Two years later, [PERSON] et al. [71] focused their attention during an abrasion test, analyzing the potential and repassivation occurrence of pure titanium and Ti\({}_{6}\)Al\({}_{4}\)V alloy in a bovine calf serum with variable pH. The aim was to investigate the different behaviors of materials, which are very common in dentistry, for a precise solution type. The results showed similar electrochemical behavior between the materials, but the commercially pure titanium exhibited a faster propensity to repassivation. In any case, it is important to underline that each experiment strongly influences the chemical composition of the working solution, affecting the tribocorrosive behavior of the studied coupling. A clear example  
Figure 5: Example of a dental implant with cutted zone. in dentistry is our saliva, which is chemically variable according to human habits (food assumed, smoking, etc.). In 2005, [PERSON] et al. [72] were interested in recreating the oral area with artificial saliva combined with some additives (citric acid, organic inhibitors) and analyzing the tribocorrosion behavior. The tests were performed for more than 10.000 cycles and in environmental conditions very close to the oral cavity, where the implants are constantly submitted to mechanical stress. The different additives and solutions influenced the material loss (the citric acid was the worst), confirming the great influence of the chemical composition of the solution on wear phenomena. On the contrary, [PERSON] et al. in 2006 [73], by electromechanical tests on pure titanium in artificial saliva solutions, varied in compositions thanks to specific inhibitors, found the opposite, as follows: the tribolayers with citric acid or anodic inhibitor became more stable with a lower coefficient of friction and lower current. This underlines the absence of a unique trend in the results, caused by the many variables involved, which requires a more intensive experimental investigation. Moreover, pH is another relevant variable and it is known that it is generally in the range of 6.2-7.4 (neutral solution), different from patient to patient and from different zones of the oral cavity but, in any case, strongly influencing the tribocorrosion occurrence. In fact, [PERSON] et al. in 2012 [74] evaluated the combined effect of corrosion and mechanical wear for the following three pH values: between 3-6 and 9, finding that the worst, because of the incomplete formation of a protective passive layer, is exactly the second. This result is almost surprising since the worst conditions did not occur when the solution was acidic (under 2 pH), but when it was neutral, which is the typical value of our mouth. The direct consequence is the high probability of tribocorrosion occurrence in the oral cavity. Together with pH, the fluoride concentration derived from common toothpaste can also have a negative effect on tribocorrosion resistance, as confirmed by [PERSON] et al. [75] and on the active dissolution of titanium alloys, as confirmed by [PERSON] et al. [76]. This demonstrates the aggressivity of the external area to biological objects such as the dental prosthesis. In [PERSON] et al. work, a near-\(\beta\) Ti13 Nb13 Zr alloy was investigated in place of the common pure titanium or Ti\({}_{6}\)Al\({}_{4}\)V alloy. The choice depends on the diffusion of toxic elements of these samples and therefore the necessity of the development new titanium samples as \(\beta\) and near-\(\beta\) titanium alloys, whose strength-to-weight ratio and excellent biocompatibility determined their diffusion in the orthodontic field. Nevertheless, their wear behavior is not so excellent and not away from the titanium samples. Lastly, [PERSON] et al.