Abstract
BackgroundDifferent crown-root angulations of maxillary central incisors can be assumed as a potential reason for many underscored outcomes of orthodontic treatments. The aim of this study was to determine the effects of the different crown-root angles on stress distributions in the maxillary central incisor’s periodontal ligament (PDL) during application of intrusive and retraction forces using a 3D finite element method.MethodsTwo models of a maxillary central incisor were constructed using ANSYS software: the first one with an angle of 166.7° (as a sample of the maxillary central incisor in a class II, division 2 patient) and the other one with an angle of 173.4° (normal angulation). Each of the samples was loaded twice by an intrusive force (0.25 N) and a retraction force (0.5 N) through the ideal position of brackets.ResultsFEM results showed little difference between stress distributions in the two models during intrusion (ten thousandth) compared to retraction (thousandth). In the application of retraction force, the stress concentration on the curved tooth was less than the other.ConclusionTo produce similar patterns of stress in the PDL, orthodontists can apply 1.18 times heavier retraction forces on the maxillary central incisors in class II, division 2 patients compared to class I patients.
Highlights
Different crown-root angulations of maxillary central incisors can be assumed as a potential reason for many underscored outcomes of orthodontic treatments
In this study, we evaluated mainly the stress distribution in periodontal ligament (PDL) which is assumed to be the biologic connector for tooth movements
Observing the labial and palatal surfaces during the application of retraction force, we found that the stress distribution near the apex and cervix was lower in the tooth with the crown-root angle of 166.7° (Table 1 and Figures 2,3,4)
Summary
Different crown-root angulations of maxillary central incisors can be assumed as a potential reason for many underscored outcomes of orthodontic treatments. The importance of tooth morphology in dental treatments has been widely emphasized. The maxillary central incisors are the most visible teeth during unstrained facial activities [1]. They are the most representatives of the mold design of the teeth and can be distinguished from the other teeth in oral cavity [2]. One of the most important aspects of tooth morphology is the axial inclination of the tooth. The correlation between axial inclination of the anterior teeth and the reference planes in cephalometrics has been of significant importance through years. Crowns of the teeth may tilt lingually or labially and this coronal inclination
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