Applicability of voice handicap index to the evaluation of voice therapy effectiveness in teachers - Niebudek-Bogusz, Ewa; Kuzańska, Anna; Błoch, Piotr; Domańska, Maja.; Woźnicka, Ewelina; Politański, Piotr; Śliwińska-Kowalska, Mariola (Nofer Institute of Occupational Medicine)