Abstract

BACKGROUND: Uncontrolled accumulation of microbial plaque and formation of biofilm on the surface orthodontic acrylic removable appliances increases the risk of enamel decalcification and periodontal diseases. The purpose of the present study was to evaluate antimicrobial activities, anti-virulence potencies, and mechanical properties of orthodontic acrylic resin containing different concentrations of Ulva lactuca (a green marine macroalga) following photo-activation against Streptococcus mutans. MATERIALS AND METHODS: Minimum inhibitory concentration (MIC) of U. lactuca was determined against S. mutans. Acrylic resin specimens with different concentrations of U. lactuca (0.2 , 0.5 , 1, 2.5 , 5, and 10 weight/weight) were fabricated. Flexural strength values, antimicrobial effects, and anti-biofilm activities of samples were assessed in comparison with original acrylic resin as the control group. Also, the expression of the virulence-associated genes was assessed by quantitative real-time polymerase chain reaction. RESULTS: U. lactuca at concentrations of 1-10 significantly reduced the S. mutans growth rate by 20.3-63.3 in comparison to the control group (P < 0.05). Therefore, the concentration of 1 of U. lactuca was considered as a MIC. The highest and lowest flexural strength values were observed in the control group (43.5 +/- 2.4 MPa) and the group with a 10 concentration of U. lactuca (19.2 +/- 1.8 MPa), respectively. Flexural strength values decreased in samples containing 2.5 , 5, and 10 concentrations of U. lactuca in comparison to the control group significantly (P > 0.05). In the disc agar diffusion test, the growth inhabitation zones around samples containing different concentrations of photo-activated U. lactuca ranged from 13 mm to 25 mm in diameter. Interestingly, the anti-biofilm activity of U. lactuca-mediated aPDT against S. mutans was dose-dependent. Additionally, the sub-MIC dose of U. lactuca (0.5 ) following photo-activation could significantly decrease the expression levels of gtfB, gtfC, and gtfD to 4.1-, 5.3-, and 7.4-fold, respectively. CONCLUSIONS: Adding photo-activated U. lactuca to the orthodontic acrylic resin at a concentration of 1 increases its antibacterial and anti-biofilm activities besides not detrimentally affects its flexural strength.