A brush (200) for cleaning a periodontal pocket between a tooth and a gum of a user. The brush (200) comprises: a handle portion (205); an arm extending (210) from the handle portion; and a brush head (211) located at an end of the arm having a plurality of brush filaments (212) extending therefrom. The brush filaments (212) are configured to be inserted into a periodontal pocket. The brush (200) can be used to assist in the treatment of gum disease by enabling a user to precisely clean periodontal pockets. The brush (200) may be for self-use. Alternatively, the brush (200) may be used by a healthcare professional such as a dentist or hygienist to treat a patient or to demonstrate its use.