Student Theses, Dissertations and Capstones

Document Type

Thesis - NSU Access Only

Degree Name

Master of Science (M.S.) in Dentistry

Copyright Statement

All rights reserved. This publication is intended for use solely by faculty, students, and staff of Nova Southeastern University. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, now known or later developed, including but not limited to photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author or the publisher.

Department

College of Dental Medicine

First Advisor

Thyagaseely Premaraj

Date of original Performance / Presentation

January 2025

Publication Date / Copyright Date

1-1-2025

Abstract

Introduction: Traditionally, lower incisor inclination has been assessed using cephalometric radiographs, which do not provide accurate information on facial and lingual bone levels. Cone-beam computed tomography (CBCT) offers three-dimensional visualization, allowing precise assessment of bone dimensions. Objective: This study aims to quantify the vertical and horizontal bone levels of mandibular incisors in untreated patients and to investigate their relationship with incisor inclination, alveolar housing angulation, and skeletal pattern using CBCT imaging. Additionally, it investigates the correlation between mandibular incisor inclination and the inclination of its alveolar housing. Methods: Fifty pre-treatment CBCTs were reviewed. For each patient, the buccal and lingual alveolar bone thickness of mandibular central incisors were measured at 3 mm, 6 mm, and 9 mm from the cementoenamel junction (CEJ). The distance from CEJ to buccal and lingual alveolar crests was also measured. The alveolar housing inclination was measured from the crestal bone between the central incisors (AH-MPA). Cephalometric data, including incisor to mandibular plane angle (IMPA), point A to Nasion to point B angle (ANB), and Frankfort Horizontal to Mandibular Plane angle (FMA), were obtained from reconstructed lateral radiographs. Correlation tests and regression analyses were conducted. Results: The mandibular incisor inclination and alveolar housing inclination were strongly correlated with each other: r = 0.843, p < 0.01. The mean distance between CEJ and alveolar crest (buccal = 1.909 ± 1.139 mm and lingual = 2.391 ± 1.360 mm) is within normal limits. Bone thickness at 3 mm from the CEJ does not exhibit any correlation with incisor inclination, skeletal profile, or amount of crowding or spacing. At 3 mm from the CEJ, 6 out of 50 patients had undetectable cortical bone (thickness = 0 mm): 4 out of 26 class II patients, and 2 out of 23 class I patients. When mandibular plane angle increases, the distance between CEJ to the visibly detected lingual alveolar crest increases (ρ = 0.307, p < 0.05). Buccal bone thickness at 6 mm and 9 mm increases with incisor proclination (ρ = 0.291, p < 0.05, and ρ = 0.616, p < 0.01). Buccal bone thickness at 6 and 9 mm from the CEJ also decreases with increased mandibular plane angle (ρ = -0.285, p < 0.05, and ρ = -0.480, p < 0.01). Lingual bone at 6 mm increases with increased alveolar housing proclination (ρ = 0.343, p < 0.05) and decreases with increased mandibular plane angle (ρ = -0.371, p < 0.01) and ANB (ρ = -0.280, p < 0.01). At 9mm from CEJ, lingual bone thickness also decreases with increased ANB (ρ = -0.412, p < 0.01) despite having no correlation with incisor proclination or mandibular plane angle. Conclusions: This study explores the relationship between cortical bone thickness, incisor inclination, and skeletal patterns. At 3 mm from the CEJ, bone thickness is consistently thin and not significantly influenced by incisor inclination or overall skeletal pattern, challenging the assumption that proclination inherently reduces buccal bone support. As lower incisor proclination increases, the buccal bone thickness below 6 mm from the CEJ also increases, indicating that buccal root torque may be a safer movement for uprighting the incisors. Conversely, the buccal bone thickness below 6 mm from the CEJ decreases with greater mandibular divergence. In more severe class II skeletal relationships, lingual bone thickness at 6 and 9 mm from the CEJ shows a marked reduction, indicating the mandibular incisors are at greater risk for dehiscence during retraction. The findings of this study suggest that the alveolar bone conforms to the natural eruptive position of the mandibular incisors. The quantity of bone available at the mandibular anterior region is approximately 1mm or less regardless of the malocclusion. These results also emphasize the importance of CBCT imaging in identifying anatomical limitations when developing individualized, periodontally responsible orthodontic treatment.

Disciplines

Dentistry

Keywords

Alveolar housing; CBCT; Mandibular incisors; Orthodontics

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