The best way to clean plastic orthodontic retainers that smelled bad, covered in white tartar and/or changing color is to soak the retainers in a solution of 1/2 water and 1/2 white vinegar or rice vinegar for 10 hours. The white tartar should be soften and come off easily after being in the solution for 10 hours.o keep your plastic orthodontic retainers clean and odor-free, soak them in a solution of 9/10 water and 1/10 white vinegar or rice vinegar for 6 to 10 hours every 2 to 3 days. Here are some plastic orthodontic retainers cleaning ideas that never worked for me: