A frenum is a naturally occurring muscle attachment, normally seen between the front teeth (either upper or lower). It connects the inner aspect of the lip with the gum.
A lack of attached gingiva (a firm, resilient type of gum), in conjunction with a high (closer to the biting surface) frenum attachment, creates tension on the margin of the gum around the neck of the tooth. This tension can result in gum recession.
Additionally, an excessively large frenum can prevent the teeth from contacting each other, resulting in a gap between the front teeth. If pulling is seen or the frenum is too large to allow the teeth to come together, the frenum is surgically released from the gum with a frenectomy.
A frenectomy is simply the surgical removal of a frenum.
When orthodontic treatment is planned or initiated, the removal of an abnormal frenum, with or without a gingival graft, can increase stability and improve the success of the final orthodontic result by preventing relapse.