Assessment of biofilm formation on ceramic, metal, and plastic brackets in orthodontic materials by new method using renG-expressing Streptococcus mutans

Objective: Oral biofilm has a high acid-producing capacity, increases the risk of enamel demineralization around brackets, and has been identified as a problem in orthodontic treatment. Here, we assessed the risk of biofilm formation by Streptococcus mutans, which is associated with the development of white spot lesions (WSL) on tooth surfaces, using multibracket devices. Methods: Various types of brackets were used for the biofilm formation assay with S. mutans coated with human saliva, immersed in renG-expressing S. mutans UA159 (strain with the luciferase gene inserted), and incubated overnight at 37 °C under aerobic conditions containing 5% CO₂. The biofilm was washed twice with phosphate-buffered saline (PBS), and 200 μL of luciferin dissolved in PBS was added to each well. The mixture was light shielded and allowed to react for 20 min. Luminescence was measured as the amount of biofilm formed by live cells on the bracket surfaces using an optical emission spectrophotometer. Results: Biofilm formation was greater in plastic brackets than in ceramic and metal brackets in a number-dependent manner. However, biofilm formation was inhibited as the plastic bracket was coated with saliva. Conclusion: For preventive treatments of WSL onset during orthodontic treatment, orthodontists should carefully select and customize brackets based on patient needs, goals, and biomechanical principles. This study developed a new measurement method using renG-expressing S. mutans UA159 to accurately assess active biofilm formation on bracket surfaces.