Date of Graduation

2017

Document Type

Thesis

Degree Type

MS

College

School of Dentistry

Department

Orthodontics

Committee Chair

Timothy Tremont

Committee Co-Chair

Chris Martin

Committee Member

Peter Ngan

Abstract

Background and Objectives: One of the most challenging questions faced in the field of orthodontics is defining the envelope of tooth movement, and answering a fundamental question, where do teeth belong in relation to bone? Incisor position, both in the maxilla and mandible, are often compromised in order to accommodate an unfavorable skeletal pattern in the sagittal, vertical, and transverse dimensions during orthodontic therapy. Optimal incisor inclination has been a continuous debate in the field of orthodontics leaving the experts divided. The question still remains what are the clinical limits of orthodontic tooth movement, which will result in the most stable occlusion without any detrimental effects to the supporting bone and soft tissues. Therefore, it is imperative to identify the optimal location of the bucco-lingual position of the incisors in the alveolar housing.;Experimental Design and Methods: A sample of 100 CBCT scans of pre-treatment orthodontic patients aged 17-20 from the private practice of Dr. Thomas Shipley was used for this study. IRB-approval was obtained. Pre-treatment CBCT images were de-identified and DICOM files were analyzed using Anatomage InVivo 5 software. CBCTs were oriented in all three planes of space which was saved used for all subsequent measurements. The images were digitized in 3D in order to extract angular measurements of interest, specifically, maxillary and mandibular incisor inclinations. Incisor inclination was derived based on reference planes from the Steiner, Andrews, and Burstone analyses for the maxilla, and from the Steiner, Andrews, Downs, Tweed, and Ricketts analyses for the mandible. The maxillary and mandibular incisors were further analyzed for the presence or absence of dehiscences and fenestrations. The data was examined using correlation and chi-square analyses.;Results: Maxillary incisors inclined in the optimal range according to Steiner, Andrews, and Burstone analyses were statistically significantly (p<.05) to result in unequal distribution of bone bucco-lingually at the center of resistance and apex. Mandibular incisors inclined in the optimal range according to Downs and Tweed analyses were statistically significantly (p<.05) to result in equal distribution of bone bucco-lingually at the apex.;Conclusions: The existing landmarks for ideal maxillary incisor inclination (as defined by Steiner, Andrews, Burstone) do not result in roots centered in the bone. The existing landmarks for ideal mandibular incisor inclination (as defined by Steiner, Andrews, Downs, Tweed, Ricketts) do not result in roots centered in bone at the center of resistance. Mandibular incisors deemed as retroclined and normoinclined according to the Downs, Tweed, and Ricketts analyses have more dehiscences than incisors with more positive inclinations.

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