This year, SMS_Shenzhen team will focus on using synthetic biologic method to prevent dental plaque. Dental plaque can be led by Streptococcus mutans, a bacteria lives in human's mouth. Clinging to the teeth in thin layers called biofilm, S. mutans digests sucrose and produces acids that can eat into enamel and cause cavities. Specifically, dextran is the main component of the biofilm. We find two enzymes, the first one is named "Dextranase", which can hydrolyze the dextran in the biofilm; and the second one is named "FruA", which can decompose the resource that S. mutans uses to produce bioflim. The gene of these two enzymes are cloned into E. coli and Lactobacillus. In our experiment, we would use E.coli to produce these two enzymes for relative measurement like enzyme activity. Then, for commercial design, we would produce leben with our Lactobacillus which can secrete these two enzymes.