# Effect of Kombucha Exposure on Corrosion Resistance of MIM Orthodontic Brackets: Geometry–Electrochemistry Coupling and Oral Health Implications (MIM-316L vs. Commercial)

## TL;DR

This study examines how kombucha affects the corrosion resistance of orthodontic brackets made with metal injection molding and commercial methods.

## Contribution

The study introduces a novel analysis of how acidic exposure impacts corrosion in orthodontic brackets, linking surface quality and electrochemical behavior.

## Key findings

- Kombucha exposure reduced corrosion resistance and repassivation potentials in MIM-316L brackets.
- Commercial brackets showed worse surface quality, increasing susceptibility to acidic conditions.
- Surface and geometric discontinuities strongly influence corrosion behavior under acidic exposure.

## Abstract

Metal Injection Molding (MIM) enables complex orthodontic-bracket geometries but can introduce surface and geometric discontinuities that act as initiation sites for crevice and pitting corrosion. The effect of acidic, kombucha-like exposure on corrosion and repassivation was assessed for MIM-316L brackets relative to a commercial comparator, and the coupling between surface quality (roughness and wettability) and localized damage at scanning electron microscopy (SEM)-identified hot-spots was examined. Kombucha was characterized by pH and titratable acidity. Surfaces were characterized by SEM, areal roughness metrics (R_a, S_a, S_z, and A2), and wettability by sessile-drop goniometry. Electrochemical behavior in artificial saliva was measured using open-circuit potential and cyclic potentiodynamic polarization (ASTM F2129/G59), and a qualitative magnetic check was included as a pragmatic quality-assurance screen. Exposure in kombucha reduced breakdown and repassivation potentials and increased passive current density, with the strongest effects co-localizing geometric discontinuities. Commercial brackets exhibited markedly poorer surface quality (notably higher S_z), amplifying acidity-driven susceptibility. These findings indicate that, under acidic challenges, surface/geometry quality dominates corrosion behavior; non-magnetic-phase compliance and simple chairside screening (e.g., magnet test), alongside tighter manufacturing controls on roughness and edge finish, should be incorporated into clinical and industrial quality assurance (QA).