Evaluating the Impact of Artificial Saliva Formulations on Stainless Steel Integrity

The biocompatibility and long-term stability of stainless steel orthodontic devices are critically influenced by their corrosion resistance in the oral environment. This study evaluates the effect of three artificial saliva formulations—Afnor (pH 7.64), Fletcher (pH 8.07, fluoride-containing), and Fusayama/Meyer (pH 6.34, acidic)—on the surface integrity and chemical behavior of 316L stainless steel over 7 and 28 days. A multi-technique approach was employed, including SEM imaging, EDX elemental mapping, XRF analysis, microhardness testing (Vickers), and the monitoring of key physico-chemical parameters (pH, conductivity, salinity, and TDS). The results indicate that Afnor saliva maintains alloy stability with minimal surface damage while Fusayama/Meyer promotes pitting corrosion and selective leaching of Fe and Ni. Fletcher saliva led to the formation of crystalline corrosion products and significant surface hardening, likely due to the interaction of fluoride with the passive layer. Microhardness values increased across all samples after 28 days, most notably in the Fletcher condition (from 191.3 HV to 256.9 HV). These findings provide valuable insights into the time-dependent degradation mechanisms of orthodontic stainless steel in varied salivary environments, emphasizing the importance of simulating realistic oral conditions in corrosion testing. The study contributes to the optimization of material selection and surface treatment strategies for improved biocompatibility in dental applications.