Biofilm Formation of Cariogenic Bacteria on Vanillin-Incorporated Orthodontic Retainer PMMA Resin

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Orthodontic retainers made of poly methyl methacrylate (PMMA) resin are generally used after finished orthodontic treatment to hold teeth in the right position and avoid the shift out from the alignment. The use of these devices can place patients at greater risk of dental caries through the biofilm accumulation of caries-associated bacteria and food debris on the rough surfaces or inherent porosities of PMMA surfaces of appliances themselves. Vanillin, the major component of flavoring agent vanilla, has been demonstrated to have antimicrobial activity against many types of microorganisms. This study aimed to evaluate antimicrobial property of vanillin-incorporated orthodontic retainer PMMA resin on the biofilm formation of cariogenic bacteria. The self-curing orthodontic retainer PMMA resin samples were produced according to the percentage of vanillin adding (0%, 0.1% and 0.5% vanillin) (SCG Chemicals, Thailand). All samples were coated with sterile unstimulated saliva. Then the cariogenic bacterial suspensions of Streptococcus mutans ATCC 25715, Streptococcus sobrinus ATCC 33478, Lactobacillus casei ATCC 334 and Lactobacillus acidophilus ATCC 314 were added and incubated at 37°C in 5% CO2 atmosphere for 48 h to allow the biofilm formation. The amount of vital biofilm was determined by WST Microbial Cell Counting Kit (Dojindo Molecular Technologies, USA) at 460 nm. One-way ANOVA and Turkey’s test were employed for the statistical analysis. A significant inhibitory effect against all tested bacteria was observed in 0.5% vanillin incorporated samples compared with 0% vanillin. The percentage of biofilm reduction was 23-45%. The adding of 0.1% vanillin showed suppressive effect only on Lactobacillus spp. In conclusion, the incorporation of 0.5% vanillin to self-curing orthodontic retainer PMMA resin could significantly inhibit biofilm formation of cariogenic bacteria (S. mutans, S. sobrinus, L. casei and L. acidophilus). Using this PMMA resin, removable orthodontic appliances with antimicrobial property can be applied to prevent dental caries or tooth demineralization in orthodontic patients.