Date of Award

2019

Embargo Period

8-1-2024

Document Type

Thesis

Degree Name

Master of Science in Dentistry

Department

Orthodontics

College

College of Dental Medicine

First Advisor

Timothy Tremont

Second Advisor

Zachary Evans

Third Advisor

Loring Ross

Abstract

Introduction: The purpose of this study was to investigate the effects of in utero levothyroxine exposure on anterior-posterior craniofacial development in a mouse model. Methods: In order to determine the effects of in utero levothyroxine exposure on anterior-posterior craniofacial development, a study group (n=19) of C57BL6 mice were exposed to high dose (~667ng per day) levothyroxine during fetal development. Mice were sacrificed day 15 post-natal. Skulls were fixed in a solution of 4% paraformaldehyde, then switched to 70% ethanol in preparation for microCT imaging. Scans were loaded into Dolphin Imaging Software and lateral cephalograms were rendered and analyzed. Results: According to the Mann-Whitney U tests, statistically significant differences were found in the maxillary position between the in utero levothyroxine exposed mice and the control mice (p<0.001). The average maxillary position angular measurement in the control group was larger at 112.19˚ (± 2.63) compared to the exposed group average of 107.25˚ (± 6.05). The exposure group exhibited an average of 5˚ degree decrease in this measure, indicating a tendency for a retrusive maxilla. This significant finding indicates that in utero thyroxine exposure can predispose offspring to maxillary skeletal retrusion. Additionally, exposure did not result in statistically significant changes to the mandible. While not a statistically significant finding, all anterior-posterior average measurement lengths were smaller for the exposure group compared to the control. Conclusions: Overall, the data supports other research that maternal exogenous levothyroxine exposure can cause aberrations in craniofacial jaw development. Excessive fetal levothyroxine exposure can predispose offspring to variations in maxillary anterior-posterior position. In humans, close monitoring of maternal thyroxine levels by primary care providers or obstetricians-gynecologists maybe important to limit craniofacial developmental aberrations.

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