Abstract: Mouthpiece (1) having vestibular shield (21) overlapping a user's teeth and gums, gases passageway means extending through said vestibular shield allowing for the passage of said gases through mouthpiece and extra oral sealing (25) means associated with gases passageway, said passageway in use causes gases to be diffused (outlets 23, 24) when exiting from gases passageway. Mouth piece may have a noseflap to seal the user's nose or provide a passageway for use'r s nasal passages. Mouthpiece may have adjustment means to alter distance between said vestibular shield and said extra-oral sealing means.