Especially fix braces may cause irritations, wounds on the inside of your cheeks and lips. Wax helps to create a barrier between the bracket and the inside of your cheeks and lips thus easening the irritation. At first you will probably use a lot of dental wax, but as your get used to your braces and the insides of your cheeks "toughen up" you may wind up using less. Your orthodontist gives you some dental wax after you get your braces put on. Most pharmacies and drug stores also carry dental wax.
How do you use orthodontic dental wax on your braces?
To use dental wax, break off a tiny bit of wax from the container, smoosh it with your fingers a bit to mold it, then place it directly on the bracket that is causing the irritation, as shown in this photo. Dental wax is non-toxic, so it's ok if you swallow it. Wax tends to break down over time, so you'll probably have to apply more after eating a meal.