Journal of Research in Medical and Dental Science 2018, Volume 6, Issue 1, Page No: 301-305 Copyright CC BY-NC-ND 4.0 Available Online at: www.jrmds.in eISSN No. 2347-2367: pISSN No. 2347-2545 Journal of Research in Medical and Dental Science | Vol. 6 | Issue 1 | February 2018 301 Changes of Pharyngeal Airway Size and Hyoid Bone Position Following Orthodontic Treatment of Class II Open Bite Patient Vahid Mollabashi 1 , Majid Mahmoudzadeh 2 , Faezeh Yousefi 3 , Maryam Farhadian 4 , Zahra Lotf Haghpanah 5 , Ali Reza Noorani 6* 1 Assistant Professor of Orthodontic Department, Dental Research Center, School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran 2 Assistant Professor of Orthodontics Department, Hamadan University of Medical Sciences, Hamadan, Iran 3 Assistant Professor of Oral & Maxillofacial Radiology Department, School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran 4 Assistant Professor of Biostatistics, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran 5 Under Graduate Student of School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran 6 Post Graduate Orthodontic Student of School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran DOI: 10.24896/jrmds.20186149 ABSTRACT The aim of this study was to investigate the changes of pharyngeal airway dimension and hyoid bone position after orthodontic treatment of class II open bite patients with extraction of two premolars in the upper arch Lateral cephalograms of 34 patients with class II open bite malocclusion in pre & post treatment used to assess the changes in hyoid position, and upper airway dimensions. All patients were treated with 0.022 * 0.028 inch preadjusted appliances after extraction of two first premolars. Anchorage was reinforced with maximum anchorage mechanics using headgears or mini-implants, depending upon the patients’ compliance. Pretreatment and post treatment variables were compared using paired t-test. The mean SPAS (0.98 ± 2.73 mm, P < 0.05) had statistically significant decrease following orthodontic treatment. No significant change was found in any other parameter about airway and hyoid bone position. In dentoskeletal measurements mandibular plane angle did not show any significant change, whereas ANB degrees (1.29 +/- 0.93, P < 0.01) decreased significantly after treatment. This effect was associated with a significant decrease in SNA degrees (0.67 +/- 0.72, P < 0.01) and significant increase in SNB degrees (0.61 +/- 0.77, P< 0.01). Upper airway size and hyoid bone position have clinically insignificant changes after orthodontic treatment of class II open bite patient with extraction of two upper premolars. Keywords: Pharynx, Open bite, Airway Management, Malocclusion HOW TO CITE THIS ARTICLE: Vahid Mollabashi, Majid Mahmoodzadeh, Faezeh Yousefi, Maryam Farhadian, Zahra Lotf Haghpanah, Ali Reza Noorani, Changes of Pharyngeal Airway Size and Hyoid Bone Position Following Orthodontic Treatment of Class II Open Bite Patient, J Res Med Dent Sci, 2018, 6 (1): 301-305, DOI: 10.24896/jrmds.20186149 Corresponding author: Ali Reza Noorani e-mail noorani_66@yahoo.com Received: 15/09/2017 Accepted: 25/12/2017 INTRODUCTION Treatment of a skeletal Class II malocclusion with an open bite and vertical facial growth pattern is always challenging for the orthodontist [1, 2]. This clinical condition frequently results from excess vertical maxillary growth, either with or without lack of vertical growth in the mandibular ramus, leading to the downward and backward displacement of the entire maxillomandibular complex [1, 2]. This pattern in turn contributes to