When you get braces, the first thing they do is place orthodontic separators. In order to put on orthodontic bands you have to slip them over the teeth like putting a ring on your finger. Teeth are usually tight (it's pretty hard to floss back there isn't it)? So, separators are these little things that are placed between the back teeth to gently move them apart just a little so the bands will fit on easily at your next appointment. In the old days these were metal and used on every tooth because they had to band every tooth. Mostly, however, we use "seps" that are like little rubber bands. The teeth will move apart slowly just a little. It feels like a little piece of food between the teeth. Some kids's teeth get a little sore, but it's not bad. Sometimes after the teeth move, the seps fall out. See your orthodontist or pediatric dentist if you need them replaced prior to your next appointment.