Abstract
Introduction: Patients undergoing orthodontic treatment are at increased risk of developing white spot lesions due to the difficulty of effectively removing dental plaque through mechanical means. Antibacterial coatings, especially titanium dioxide (TiO2), on stainless steel orthodontic appliances are becoming increasingly popular. However, the need for ultraviolet light activation limits the practical use of TiO2 coatings. A novel coating combining nanostructured anatase rutile titanium dioxide with amorphous carbon (NsARC) could potentially overcome the need for light activation. This study aimed to evaluate the physical properties, antibacterial properties, and cytotoxicity of the NsARC coating, as well as to assess its effect on the static frictional force when applied to orthodontic brackets and wires.
Materials and Methods: The microscopic surface characteristics of both coated and uncoated discs were qualitatively assessed using scanning electron microscopy. Colour variations of the coated discs were measured using ImageJ software on digital photographs. Contact angles of the discs were measured with a goniometer. Surface roughness was determined with an optical profilometer, while the hardness and elastic modulus of the coating were measured using a nanoindenter. To evaluate contact antibiofilm properties, the number of colony-forming units of Streptococcus mutans NCTC 10449 cells attached to uncoated stainless steel (negative control), NsARCcoated, and copper (positive control) discs were calculated. The diffusible antibacterial properties of the NsARC-coating were assessed by measuring the zone of growth inhibition on BHI agar plates seeded with S. mutans. Cytotoxicity towards human gingival fibroblasts (HGFs) was evaluated using the PrestoBlue™ metabolic activity assay for both uncoated stainless steel and NsARC-coated discs. Finally, the static frictional force between coated orthodontic brackets and wires was measured with a universal testing machine.
Results: The coated discs displayed a range of grey intensities, indicating variations in colour. They were more hydrophilic and rougher compared to the uncoated stainless steel discs. The coating had lower hardness and elastic modulus than the uncoated stainless steel. The mean viable cell count from the NsARC-coated discs was 7.8 times lower than that from the uncoated stainless steel discs, demonstrating an antibiofilm effect comparable to that of copper discs in both ambient light and dark environments. However, unlike the copper discs, the coated discs did not exhibit any diffusible antibacterial effects. Both uncoated stainless steel and NsARC-coated discs exhibited mild cytotoxicity towards HGF cells, with the cytotoxicity of the coated discs increasing over time. Additionally, the NsARC coating resulted in increased static frictional force between orthodontic brackets and wires.
Conclusions: The NsARC coating demonstrated a contact antibiofilm effect in the dark similar to that of copper. The coating also increased the hydrophilicity and roughness of stainless steel and raised the static friction between orthodontic brackets and wires. The relatively low hardness and elastic modulus of the coating suggest it may be prone to damage in clinical settings. Further research is necessary to investigate the long-term cytotoxic effects and clinical effectiveness of the NsARC coating