Background: Acrylic plates on removable orthodontic appliances can be a place for plaque and food scraps to facilitate Streptococcus sanguinis microorganisms to breed. Adding nanoparticle of titanium dioxide to acrylic plate may provide antibacterial activity. Objecttive: To see effect of TiO2 nanoparticle on acrylic plate to growth of Streptococcus sanguinis. Method: This research is a laborat…