A frenum is a large muslce that is usually located between the front teeth. It is a very strong muscle that can push teeth apart and/or cause recession.
Your orthodontist or dentist may have recommended that your frenum be removed. When the frenum attaches close to the teeth, it can cause the teeth to separate even though braces have brought the teeth together. The teeth are more suspectible to gum disease as the seal between the tooth and the gum can be disrupted as the frenum moves. A frenum may also cause recession, or pulling on your gums to cause them to pull back from your tooth.