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

Chin Lin

Date of original Performance / Presentation

January 2024

Publication Date / Copyright Date

1-1-2024

Abstract

Objectives: The objective of this study was to use intraoral scans and digital measurements to determine the difference between two frequently used practices, Little’s Irregularity Index (LII) and Merrifield’s Space Analysis (MSA), that evaluate mandibular incisor crowding. Methods: In this retrospective study, 100 digital model samples were collected from NSU’s postgraduate orthodontic iTero scanners, in which 20 samples were allocated into each of the five incisor irregularity categories: ideal alignment (0-0.9mm); minimal (1-3.9mm), moderate (4-6.9mm), severe (7-9.9mm), and extreme (more than 10mm) irregularities. Both LII and MSA were used to measure mandibular incisor crowding on digital models using Dolphin Imaging 11.95 Premium software. Data were analyzed by use of the general linear model and a paired t-test was used to compare LII to MSA for each of the five irregularity index categories. Intra-and inter-rater reliability were confirmed by a concordance correlation coefficient. Results: The general linear model found LII to have a significant effect on MSA (P < 0.001) with a slope estimate of 0.37, while the intercept (P = 0.955) was found to be non-significant. Except for the ideal alignment category of LII, MSA and LII measurements were statistically different. The average difference of (LII-MSA) were 0.08mm (SE 0.09) (ideal), 1.61mm (SE 0.19) (minimal), 3.57mm (SE 0.24) (moderate), 5.34mm (SE 0.31) (severe), and 7.13mm (SE 0.61) (extreme) for each category. Conclusions: 1) There is a difference between LII and MSA measurements for the categories: mild, moderate, severe, and extreme irregularities when obtained digitally. 2) LII and MSA should not be used interchangeably to calculate mandibular incisor crowding unless the incisor irregularity index is “ideal.” 3) As the irregularity index increases, the dispersion between LII and MSA measurements increases. 4) As LII increases, MSA increases but not as significantly (slope estimate of 0.37).

Disciplines

Dentistry

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