Date of Award


Document Type


Degree Name

Master of Dental Science (MDS)



Research Advisor

Edward F. Harris, Ph.D.


Terry M. Trojan, D.D.S., M.S. Jere L. Yates, D.D.S., M.S.


Airway, CBCT, Extraction, Oropharynx, Orthodontic, Premolar


Orthodontic correction of tooth size versus arch size discrepancy (TSASD) can be achieved with two distinct methods of treatment. The first involves the extraction of teeth to gain the space needed for tooth alignment. The second relies on arch expansion to gain the space needed for correction. In recent decades, arguments for and against the extraction of teeth for orthodontic purposes have become increasingly important, particularly in regards to oropharyngeal airway size. Purpose: The purpose of this study is to determine whether there is a decrease in oropharyngeal dimensions following the extraction of four premolars and subsequent orthodontic therapy. Methods: Pretreatment and posttreatment CBCT images were taken on 88 healthy, adolescent orthodontic patients (27 with 4 premolar extraction, 61 non-extraction). Cephalometric measurements, as well as 3-dimensional analysis of the oropharyx were performed before and after treatment. Results: The extraction group had significantly larger measurements for Anterior Facial Height (AFH), Sella Perpendicular to A Point, SNA, ANB, Facial Convexity, and Y-Axis. The non-extraction group had significantly larger measurements for Sella Perpendicular to B Point. For Sella Perpendicular to L6 Mesial and U6 Mesial, the extraction group had greater mesial movement, which was likely due to Class II treatment mechanics. The measurements that were found to be statistically insignificant between extraction and non-extraction groups were: Atlas Vertebra to Posterior Nasal Spine, Hyoidale to Frankfort Horizontal, Posterior Soft Palate to Posterior Pharyngeal Wall, SNB, Upper Pharyngeal Plane Width, Upper Pharyngeal Plane Area, Middle Pharyngeal Plane Width, Middle Pharyngeal Plane Area, Lower Pharyngeal Plane Width, Lower Pharyngeal Plane Area, Middle Pharyngeal Plane Airway Volume, Inferior Pharyngeal Plane Airway Volume, and Total Pharyngeal Plane Airway Volume. Conclusions: At the level of the posterior nasal spine (PNS), the posterior soft palate, and the tip of the epiglottis, there were net increases in oropharyngeal widths, cross-sectional areas, and oropharyngeal volumes for both treatment groups. There was also no constriction of the oropharyngeal airway during either extraction or non-extraction treatment and there is no quantitative evidence that reducing arch perimeter has any effect on oropharyngeal size.