Variation in Surface Morphology and Microstructure of 316L Biomedical Alloys Immersed in Artificial Saliva

ObjectiveThe objective of this study was to compare changes in the surface morphology and microstructure of different types of 316L orthodontic bracket alloys such as one-piece injection molding (Group A) and two-piece soldering (Group B) that were immersed in artificial saliva solution (37 °C/pH 7.0) for various periods.MethodsAn optical microscope, atomic force microscope, X-ray diffractometer, and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer were used to investigate the surface properties including microstructure, roughness, and chemical compositions.ResultsThe study results demonstrated that corrosion in both types of orthodontic brackets (A and B) initially occurred in the 3rd month, and an austenite (γ) → [γ + (Fe, Cr)O compound] microstructure transition occurred in the matrix of the bracket body when both orthodontic brackets were subjected to immersion for more than 3 months.ConclusionThe Group A brackets, which exhibited better surface characteristics, maintained a low and constant level of surface roughness after various immersion times. Therefore, a modified metal injection molding (MIM) process based on a thermosetting resin developed with 316L stainless steel showed fewer pores and higher corrosion resistance.