Effect of incorporating undoped or silver-doped photocatalytic titanium dioxide on the antifungal effect and dynamic viscoelastic properties of long-term acrylic denture liners

Objectives: The current study aimed to investigate the effect of incorporating undoped or silver-doped titanium dioxide nanoparticles (TiO2-NPs and Ag-doped TiO2-NPs) on the antifungal activity and dynamic viscoelastic properties of soft acrylic denture liners. Materials and methods: One soft acrylic liner material was used (COE-SOFT, GC America, USA). Triphasic TiO2-NPs were purchased from Nanotech, Egypt. Half the amount of the TiO2-NPs was doped with silver (≈100 ppm). The efficiency of the doping process was validated by FTRI analysis. Ultraviolet-visible spectrophotometer was used to measure the absorption range of both powders (TiO2-NPs and Ag-doped TiO2-NPs). For the antifungal activity test, eight groups of liner discs were prepared: three unfilled groups (liner only); two TiO2 groups (liner containing 5 wt% TiO2-NPs) and three Ag-doped TiO2 groups (liner containing 5 wt% Ag-doped TiO2-NPs). The discs were inoculated and incubated with Candida albicans then subjected to one of three different lighting conditions: darkness, ultraviolet (UV) or visible light (VL). The (unfilled-dark) group was considered the control. After exposure to the specified lighting condition, the adherent fungi were detached from the liner discs' surfaces and the resultant fungal solutions were incubated then the number of colony forming units was counted. For the dynamic viscoelastic properties, three groups were tested; control (liner only), TiO2 group (liner containing 5 wt% TiO2-NPs) and Ag-doped TiO2 group (liner containing 5 wt% Ag-doped TiO2-NPs). The properties were measured using a dynamic mechanical analyzer. The data were statistically analyzed. Results: The FTIR revealed the success of the doping process without drastic changes in the TiO2 phase ratios. The Ag-doped TiO2-NPs had a wider absorption spectrum with greater photoactivity in the visible light range compared to pure TiO2-NPs. Regarding the antifungal activity, the Ag-doped TiO2 group subjected to visible light had the highest antifungal effect while the control group (unfilled liner subjected to darkness) had the highest number of colony forming units. All groups subjected to UV showed comparable antifungal activity regardless of their composition. Regarding the dynamic viscoelastic properties, both the control and TiO2 groups had higher tan delta (loss tangent) compared to the Ag-doped TiO2 group indicating a better cushioning effect for the two former groups. However, the latter group still had a clinically acceptable tan delta value. Conclusions: Silver-doping increases the photoactivity of TiO2-NPs within the visible light range. Incorporating Ag-doped TiO2-NPs into soft acrylic denture liners imparts a potent antifungal activity against Candida albicans upon illumination with visible light. This is accompanied by a reduction in the cushioning effect of the liner, however it still lies within the clinically acceptable range