If you dream about flossing your teeth, it's possible that you are trying to deal with an issue or solve a problem in your waking life. Or perhaps you are preparing to cope with something that is concerning or bothering you.
If you make your gums bleed from flossing in a dream it's possible that you have had a loss of some type lately or anticipate one in the near future. It could also represent your fears about a some negativity in your life and the consequences of your actions.
Another point of view is that you are trying to get to the root of something and digging deep to find it.
Perhaps you are concerned about your appearance and how you look to others. You may feel you need to pay closer attention to your routine or have been in order to impress those around you.
You may also feel a desire to have some routine and consistency in your life now if it has been erratic until recently.