Mitigating Monomer Leaching and Resin-Related Hypersensitivity in Removable Orthodontics Through Bio-Inspired Surface Modifications: A Narrative Review

Background: During clinical service, removable orthodontic appliances are continuously exposed to environmental challenges that may compromise material stability and contribute to potentially increasing the risk of local inflammatory responses and hypersensitivity reactions. Method: A literature search was conducted using PubMed/MEDLINE, Scopus, and Web of Science databases. Studies investigating bio-inspired and surface-engineering approaches applicable to orthodontic polymers, acrylic resins, aligner materials, and related dental biomaterials were considered. Evidence from orthodontic adhesives and non-bio-inspired barrier coatings was included when relevant as comparative or translational support. Particular attention was given to polydopamine coatings, polyphenol- and tannic acid-based coatings, chitosan systems, peptide-functionalized surfaces, titanium and titanium oxide-based modifications, nanoparticle-enriched coatings, biomimetic hydrogel-like barriers, and conventional barrier coatings used as comparators. Results: Available evidence suggests that surface modifications reduce monomer diffusion, bacterial adhesion, biofilm formation, and improve cellular responses. Bio-inspired and titanium-based coatings show particular promise by enhancing biocompatibility while providing antimicrobial, antioxidant, anti-inflammatory, and protective barrier properties. Conclusions Bio-inspired surface engineering is a promising approach to improve the biological safety of removable orthodontic appliances. However, further standardized in vitro, in situ, and clinical studies are needed to confirm their long-term stability, durability, and clinical effectiveness in reducing hypersensitivity and other adverse biological effects.