Date of Award

1-1-2021

Document Type

Thesis

Degree Name

Master of Science in Dentistry

Department

Orthodontics

College

College of Dental Medicine

First Advisor

Timothy J. Tremont

Second Advisor

Martin Steed

Third Advisor

Loring Ross

Fourth Advisor

Zachary Evans

Abstract

Introduction: Currently, there is no consensus in the orthodontic or OMFS literature regarding diagnosis of transverse dental arch discrepancies and to what extent discrepancies in underlying maxillary and mandibular transverse jaw dimensions are an etiology. In addition, there is an absence of discussion regarding possible differences in maxillary anterior versus posterior transverse jaw discrepancies. The purpose of this investigation was to: 1) evaluate a dental cast versus CBCT method for diagnosing skeletal transverse discrepancies, 2) assess whether dental cast or CBCT determined posterior transverse discrepancies differ from anterior transverse discrepancies, and 3) assess if any differences exist in skeletal transverse discrepancies between patients with Class I, II and III skeletal malocclusions. Methods: Retrospective data including intraoral scans of the maxillary and mandibular arches and CBCT scans were collected from 40 patients prior to orthodontic treatment. The sample was divided into CI (12 subjects), CII (18 subjects) and CIII (10 subjects) subgroups based on their skeletal anteroposterior diagnosis. Using maxillary and mandibular digital casts, dental arch widths were measured at the canines, first premolars and first molars and the measurements adjusted for optimal tooth inclinations. CBCT measurements were also made between the right and left first molars (M), first premolars (P) and canines (C) at the following vertical levels: 1) the estimated center of resistance of the tooth, 2) the root apices and 3) an estimated center of basal bone. Finally, a posteroanterior ephalogram was rendered from each subject’s CBCT scan and the distance between right and left Jugale was compared to the distance between right and left Antegonion. The differences between maxillary and mandibular measurements (Δ) on the digital models, CBCTs and PA cephalograms were compared. Results: For the digital cast analysis Δ at each location (canine, premolar and molar) was significantly different, however, the average Δ for each location was not significantly different between subgroups. For the CBCT analysis, there were significant differences between each location (p<.0001) but no consistency between vertical points for each location. Additionally, the average Δ was significantly different between subgroups at each location, indicating no correlation. For the PA cephalogram analysis, no significant differences were found in the average skeletal widths or the average Δ between subgroups. We found no significant correlation between Δ at each location on the digital models and CBCTs. Conclusions: When maxillary skeletal transverse discrepancies are present, they often differ between the anterior and posterior. Transverse discrepancies were not significantly different between skeletal Class I, Class II and Class III subjects. No maxillary and mandibular skeletal landmarks were identified to assess transverse skeletal discrepancies. A dental cast analysis appears to be a more effective method for assessing transverse jaw discrepancies.

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