Impact of toothbrushing on aesthetic and mechanical properties of hydrophilic antibacterial coating materials for orthodontic clear retainers

This study aims to analyze the aesthetic, mechanical, and antibacterial properties of clear retainer materials with an antibacterial coating. Specifically, it evaluates whether the coating can retain its effectiveness after repeated toothbrushing by assessing material integrity, surface roughness, and bacterial adhesion in vitro. Four types of 1.0-mm thermoplastic sheets widely used in orthodontic clear retainers were tested: PUL (Magicfoil R, Osstem, Korea), PUC (Magicfoil R with a hydrophilic antibacterial coating), PUZ (Zendura, Bay Materials, USA), and PET (CA Retention Foil, Scheu-Dental, Germany). The PUL, PUC, and PUZ sheets were composed of polyurethane (PU), whereas the PET sheets were made of polyethylene terephthalate glycol (PETG). Flexural strength, tensile strength, and cyclic load tests were conducted to compare the mechanical properties of these four materials, and transparency was compared to evaluate aesthetic properties. The surface roughness of the specimens and the antibacterial ability against Streptococcus mutans were measured before and after toothbrushing. The antibacterial coating did not change the mechanical or aesthetic properties of the retainer material. After brushing, all types' materials had similar surface roughness values as before brushing. Additionally, the antibacterial coating group (PUC) exhibited lower bacterial adhesion than the uncoated group (PUL), with reductions of 36% before and 40% after toothbrushing. The difference was statistically significant before toothbrushing (p < 0.05), but not after simulated toothbrushing. These results confirm that the hydrophilic coating has an antibacterial effect and that this effect can be maintained even after repeated toothbrushing.