# Evaluating the Impact of Artificial Saliva Formulations on Stainless Steel Integrity
## 3 Results and Discussion
### Morphological and Chemical Composition
The alloy's composition is essentially stable, reflecting that the neutral pH and lack of aggressive ions (no fluoride and moderate chloride) enable the stainless steel's passive layer to remain intact. The presence of thiocyanate (SCN\({}^{-}\)) did not produce any obvious effect on the bulk composition; any influence (SCN\({}^{-}\) can in some cases promote corrosion) was minimal in this static exposure. There is no strong evidence of leaching of Fe, Ni, or other elements in the Afnor solution--only a hint of Cr enrichment and Fe/Ni reduction is evident by 28 days, which indicates very slight selective dissolution. In practical terms, the steel's elemental stability in Afnor saliva suggests excellent corrosion resistance in a neutral saliva environment, with no significant depletion of important elements. Regarding the Fusayama/Meyer artificial saliva (acidic pH 6.3), after 7 days of exposure in a more acidic medium--containing chlorides, sulfide (S2\({}^{-}\)), phosphate, urea, etc.--the XRF changes are still relatively small but are more noticeable than in Afnor. Fe remains high (\(\sim\)67.8% \(\rightarrow\) -67.8% at 7 days, essentially unchanged), but Ni shows a slight decrease even at 7 days (a drop in the order of 0.1-0.2%). A small Ni loss early on is significant because Ni is known to dissolve out of stainless steel more readily under acidic conditions [20]. Cr at 7 days is roughly constant or up slightly, again hinting that a bit of Fe/Ni has been removed, leaving the surface richer in Cr. These 7-day results suggest the onset of corrosion in acidic saliva, albeit limited--Ni (and possibly some Fe) is beginning to leach, while Cr is left behind in the passive film. Twenty-Eight-Day Exposure: By 28 days, the effect of the acidic environment becomes clearer. The Fe content of the steel drops modestly (to \(\sim\)67.3%, a few tenths below the initial immersion), and Ni decreases more noticeably (down to roughly 12.0%, compared to \(\sim\)12.7% initially). This Ni depletion is a strong indicator of corrosion--nickel is being released from the alloy into the solution. In fact, studies have shown that a low pH greatly accelerates Ni ion release from stainless steel, much more so than a neutral pH [20]. Our results align with that--Ni is evidently one of the more \"mobile\" elements under acidic conditions. Fe also decreases, though to a lesser extent. The concurrent rise in Cr content (to \(\sim\)17.5% vs. 17.1% initially) confirms that Cr is preferentially retained on the corroded surface [21]. In essence, as Ni and some Fe atoms leach out, the remaining surface matrix becomes enriched in the more corrosion-resistant Cr (and to a degree Mo). Mo shows a slight uptick (perhaps \(\sim\)2.3% vs. 2.1%initial), suggesting that Mo is not leaching but is instead staying or even concentrating in corrosion products--consistent with Mo's known role in reinforcing the passive film by forming insoluble compounds [22]. With respect to Fletcher artificial saliva (basic pH 8.07 with fluoride), after 7 days of exposure, which is basic and contains fluoride (NaF), the composition already shows some early signs of interaction--Fe drops slightly from the initial 67.92% to 67.64%, more than in Afnor or Fusayama/Meyer at this point. Ni decreases modestly from 10.238% to 10.270%, then is up slightly--possibly due to minor measurement variation. Cr slightly decreases from 17.167% to 16.955%. Mo increases from 2.067% to 2.140%, and Co increases more visibly from 0.263% to 0.315%. This suggests a shift in surface composition, possibly due to fluoride ions attacking the passive film, leading to selective leaching. After 28 days, the effects of fluoride and basic pH are more pronounced--Fe further decreases to 67.45%--the largest Fe loss among the three media. Cr drops from 17.167% to 16.813%, more significantly than in other media--indicating that Cr is dissolving, which is atypical and concerning. Ni increases slightly, but still fluctuates near the baseline (~10.310%).