# Evaluating the Impact of Artificial Saliva Formulations on Stainless Steel Integrity
## 4 Conclusions  
This study comprehensively investigated the corrosion behavior and surface transformations of AISI 316L stainless steel after immersion in three artificial saliva formulations (Afnor, Fletcher, and Fusayama/Meyer) over 7 and 28 days. The Afnor solution (neutral pH) maintained the integrity of the stainless steel surface with minimal morphological or compositional changes, indicating a stable passive film. The Fletcher solution (basic with fluoride) promoted moderate surface degradation, including the formation of crystalline corrosion products and selective elemental depletion, particularly of Fe and Cr. The Fusayama/Meyer solution (acidic) caused the most aggressive corrosion, with evident pitting, surface roughening, and significant leaching of Fe and Ni, as confirmed by the SEM, EDX, and XRF analyses. The FTIR spectroscopy revealed increasing surface hydroxylation and phosphate-related bands, particularly in the Fusayama/Meyer and Fletcher conditions, indicating the formation of corrosion byproducts and reprecipitated compounds. The EDX mapping highlighted chloride and sodium accumulation in all environments, with calcium and phosphorus precipitation notably observed in the acidic environment (Fusayama/Meyer), suggesting secondary surface mineralization. The Vickers and Rockwell microhardness measurements showed an overall increase in surface hardness over time in all conditions. The most pronounced hardening occurred in the Fletcher solution, likely due to the formation of hard crystalline corrosion products or sub-surface phase changes. The findings underline the critical influence of the chemistry of artificial saliva on the degradation behavior of stainless steel in simulated oral environments. These insights are directly applicable to the design, selection, and performance evaluation of orthodontic and dental metallic materials intended for prolonged use in the oral cavity. Future work may focus on surface coatings or alloy modifications to enhance resistance in more aggressive media.  
Conceptualization, D.L.B. and V.G.; methodology, A.C.M., N.L.B. and E.E.H.; formal analysis and investigation, C.T., D.L.B. and V.G.; writing--original draft preparation, D.L.B. and V.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by \"Dunarea de Jos\" University of Galati, Romania, grant research no. 7954/31.03.2025.  
Not applicable.  
**Data Availability Statement:** All data analyzed in this study are included in the published article.  
**Conflicts of Interest:** The authors declare no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Saliva Type** & **D1 (7 Days)** & **D2 (7 Days)** & **HV** & **HRA** & **D1 (28 Days)** & **D2 (28 Days)** & **HV** & **HRA** \\  & [**um**] & [**um**] & (**7 Days)** & (**7 Days)** & [**um**] & [**um**] & **[**um**]** & **(28 Days)** & **(28 Days)** \\ \hline [PERSON] & 98.25 & 96.19 & 196.1 & 56.5 & 75.75 & 101.92 & 234.9 & 60.3 \\ [PERSON]/[PERSON] & 96.82 & 100.18 & 191.1 & 55.9 & 93.22 & 97.09 & 204.7 & 57.5 \\ [PERSON] & 97.97 & 98.90 & 191.3 & 55.9 & 90.62 & 79.27 & 256.9 & 62.1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Hardness results for samples stored in artificial saliva for 7 and 28 days.