Student Theses, Dissertations and Capstones

Document Type


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.


College of Dental Medicine

First Advisor

Abraham B Lifshitz

Second Advisor

Sergio Real

Third Advisor

Gisela Contasti Bocco

Publication Date / Copyright Date



Nova Southeastern University


Introduction: Detection of impacted teeth by the orthodontist is imperative for diagnosis and treatment planning. A tooth is impacted when it has arrested eruption due to the presence of a clinically or radiographically visible physical barrier in the path of eruption. The most commonly impacted teeth are third molars, followed by maxillary canines and mandibular second premolars. When referring to mandibular second molar (MM2) impaction, prevalence ranges from as low as 0.06-0.65%1-5, to as high as 1.36% and 1.8%. Numerous studies have identified etiologic risk factors for MM2 impaction, such as mesial crown angulation, dental crowding, morphological tooth anomalies, and a smaller distance between the mandibular first molar and the mandibular ramus.4-8 Studies also suggest a positive correlation between vertically directed condylar growth and impaction rates of mandibular second and third molars. However, to this day, few studies have correctly used lateral cephalograms to evaluate the skeletal morphology of the mandible and its relationship mandibular second molar impaction.5,9 Thus, the goal of this research study was to evaluate if there is a relationship between MM2 impaction and Class II malocclusions. Methods: In this retrospective study, 75 subjects with impaction of MM2 were compared to a control group of 200 subjects with normal eruption of MM2. Based on evaluation of panoramic x-rays, MM2 was classified as impacted if its complete eruption to occlusal plane height was prevented by an abnormal contact with another tooth in the same arch, and when it remained unerupted beyond ¾ root formation. The corresponding lateral cephalograms were then traced and analyzed using Dolphin Imaging Software available in the Nova Southeastern University Post-Graduate Orthodontic Clinic. Frequencies and percentages were calculated for all categorical variables, and means and standard deviations were calculated for continuous measures. Wilcoxon-Mann-Whitney-U-tests was used for statistical comparisons between groups, and a logistic regression model was used to examine the relationship between various independent variables and the presence of impaction. Results: No association was found between gender, age, and mandibular second molar (MM2) impaction. The sagittal analysis showed that MM2 impaction was more commonly seen in skeletal Class II patients (p<0.05). However, mandibular corpus length (Xi-Pm) and eruption space (MM1-Xi) showed no statistically significant difference between groups. Vertical analysis in the MM2 impaction group showed significantly larger values for SN-MP, FH-MP (FMA), and SGn-FH (p<0.05). Lastly, the logistic regression model showed that hyperdivergent patients were nearly four times more likely to have MM2 impaction than hypodivergent patients (OR=3.99, p=0.009). Conclusions: Although Class II malocclusions were more likely to present with MM2 impaction than Class I malocclusions, this study could not confirm that a short mandible or one that has reduce retromolar eruption space is the cause of MM2 impaction. Instead, our findings showed the importance of evaluating the vertical morphology of the mandible and its association with mandibular second molar impaction. This seems to be a useful finding for treatment planning, especially in cases that are being planned for maximum mandibular anchorage or distalizing mechanics.




Class II malocclusions, Impaction, Mandibular second molars, Orthodontics, Retrognathic mandibles



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