A respiration mask assembly including: a mask body having a front part that defines a front opening adapted to communicate fluidly with a gas supply, and a rear part that defines a rear opening opposite to the front opening in a horizontal direction; a forehead support beam extending outwardly from and pivoted to the front part of the mask body so as to rotate relative to the mask body about a first axis transverse to the horizontal direction; and a worm pivoted to the front part of the mask body. The forehead support beam has a toothed pivot end engaging the worm such that rotation of the worm about a second axis transverse to the first axis results in rotation of the forehead support beam about the first axis.