Photocatalytic antimicrobial effect of titanium dioxide coated clear-aligners on Streptococcus mutans and evaluation...

This study evaluated the photocatalytic antimicrobial effect of titanium dioxide (TiO₂)-coated clear aligners against Streptococcus mutans and assessed the impact of TiO₂ coating on surface microhardness and optical transparency.

Clear aligner samples (10 × 10 × 2 mm) were coated with different concentrations of TiO₂ (1 %, 2 %, and 4 %) via submerging. Uniformity of particle distribution and surface microhardness were measured using scanning electron microscope (SEM) and Vickers hardness testing, respectively. Optical transparency was assessed via ultraviolet-visible spectrophotometry. After incubation in artificial saliva, samples were exposed to ultraviolet A (UVA) at 320 nm for 1 min with an energy density of 18.75 J/cm²). Biofilm inhibition was evaluated by crystal violet colorimetric assay, measuring optical density at 595 nm. Expression of gtfB gene was analyzed via quantitative real-time polymerase chain reaction.

SEM images confirmed uniform nanoparticle distribution with no surface damage. The combination of TiO₂ coating and UVA exposure significantly reduced biofilm formation, with the 4 % TiO₂ group demonstrating the highest inhibitory effect compared to the control group (P < 0.001). Additionally, expression of the gtfB gene was significantly downregulated in this group (-6.35 ± 0.30). Surface microhardness showed a non-significant increase with higher TiO₂ concentrations, suggesting enhanced wear resistance without compromising material properties. However, the 4 % TiO₂ coating resulted in a significant reduction in optical transparency compared to other groups (P < 0.01).

While 4 % TiO₂ coating with UVA activation achieved the strongest antibiofilm effect, it compromised optical transparency. The 2 % TiO₂ coating preserved aesthetics and still provided substantial antimicrobial activity, making it the more practical clinical option.