This study aimed to investigate the effect of ozone ultrafine bubble water (OUFBW) on the formation and growth of Candida albicans (C. albicans) biofilms and surface properties of denture base resins. OUFBWs were prepared under concentrations of 6 (OUFBW6), 9 (OUFBW9), and 11 ppm (OUFBW11). Phosphate buffered saline and ozone-free electrolyte aqueous solutions (OFEAS) were used as controls. Acrylic resin discs were made according to manufacturer instructions, and C. albicans was initially cultured on the discs for 1.5 h. A colony forming unit (CFU) assay was performed by soaking the discs in OUFBW for 5 min after forming a 24-h C. albicans biofilm. The discs after initial attachment for 1.5 h were immersed in OUFBW and then cultured for 0, 3, and 5 h. CFUs were subsequently evaluated at each time point. Moreover, a viability assay, scanning electron microscopy (SEM), Alamar Blue assay, and quantitative real-time polymerase chain reaction (qRT-PCR) test were performed. To investigate the long-term effects of OUFBW on acrylic resin surface properties, Vickers hardness (VH) and surface roughness (Ra) were measured. We found that OUFBW9 and OUFBW11 significantly degraded the formed 24-h biofilm. The time point CFU assay showed that C. albicans biofilm formation was significantly inhibited due to OUFBW11 exposure. Interestingly, fluorescence microscopy revealed that almost living cells were observed in all groups. In SEM images, the OUFBW group had lesser number of fungi and the amount of non-three-dimensional biofilm than the control group. In the Alamar Blue assay, OUFBW11 was found to suppress Candida metabolic function. The qRT-PCR test showed that OUFBW down-regulated ALS1 and ALS3 expression regarding cell-cell, cell-material adhesion, and biofilm formation. Additionally, VH and Ra were not significantly different between the two groups. Overall, our data suggest that OUFBW suppressed C. albicans growth and biofilm formation on polymethyl methacrylate without impairing surface properties.

This study aimed to investigate the cleansing effects of grapefruit seed extract (GSE) on biofilms of Candida albicans (C. albicans) formed on denture-base resin and the influence of GSE on the mechanical and surface characteristics of the resin. GSE solution diluted with distilled water to 0.1% (0.1% GSE) and 1% (1% GSE) and solutions with Polident® denture cleansing tablet dissolved in distilled water (Polident) or in 0.1% GSE solution (0.1% G+P) were prepared as cleansing solutions. Discs of acrylic resin were prepared, and the biofilm of C. albicans was formed on the discs. The discs with the biofilm were treated with each solution for 5 min at 25°C. After the treatment, the biofilm on the discs was analyzed using a colony forming unit (CFU) assay, fluorescence microscopy, and scanning electron microscopy (SEM). In order to assess the persistent cleansing effect, the discs treated with each solution for 5 min were aerobically incubated in Yeast Nitrogen Base medium for another 24 h. After incubation, the persistent effect was assessed by CFU assay. Some specimens of acrylic resin were immersed in each solution for 7 days, and changes in surface roughness (Ra), Vickers hardness (VH), flexural strength (FS), and flexural modulus (FM) were evaluated. As a result, the treatment with 1% GSE for 5 min almost completely eliminated the biofilm formed on the resin; whereas, the treatment with 0.1% GSE, Polident, and 0.1% G+P for 5 min showed a statistically significant inhibitory effect on biofilms. In addition, 0.1% GSE and 0.1% G+P exerted a persistent inhibitory effect on biofilms. Fluorescence microscopy indicated that Polident mainly induced the death of yeast, while the cleansing solutions containing at least 0.1% GSE induced the death of hyphae as well as yeast. SEM also revealed that Polident caused wrinkles, shrinkage, and some deep craters predominantly on the cell surfaces of yeast, while the solutions containing at least 0.1% GSE induced wrinkles, shrinkage, and some damage on cell surfaces of not only yeasts but also hyphae. No significant changes in Ra, VH, FS, or FM were observed after immersion in any of the solutions. Taken together, GSE solution is capable of cleansing C. albicans biofilms on denture-base resin and has a persistent inhibitory effect on biofilm development, without any deteriorations of resin surface.