Effect of force directions in maxillary anterior teeth retraction with skeletal anchorage : finite element analysis

Name: Nantaporn Reunpol

keyword: Skeletal anchorage

; Finite element analysis

; Retraction

Abstract: The aim of the study was to compare the force directions to allow bodilylike parallel retraction of maxillary anterior teeth. To calculate the tooth elements, surface model of the tooth was made based on a dental study model (i21D-400C ; Nissin Dental Products, Kyoto, Japan). This procedure consisted of 3 steps: Firstly, sectional images of the dental study model were taken by using dental cone-beam computed tomography (i-CAT, U.S.A.). Secondly, the finite element model was developed using MSC Patran (MSC Software, Inc.,USA.). The thickness of periodontal ligament (PDL) was considered to be uniform (0.25 millimeters). The alveolar bone was constructed to follow the curve of cementoenamel junction. The thickness of cortical bone was 0.5 millimeters. The bracket slot was 0.018x0.025 inch (Gemini, 3M Unitek, U.S.A.), in which the 0.016x0.022 inch stainless steel archwire was inserted. Brackets of the anterior teeth were ligated firmly to the archwire. On these teeth, the archwire and the brackets were moved as an united body. Alternatively, buccal tubes of the posterior teeth were loosely engaged to the archwire so that they could be slided along the archwire, but sagittal rotation of the archwire was restricted by bracket slots. The frictional coefficient was ignored. Mini-screws or fixed points were placed in alveolar bone between the second premolars and the first molars in position of 3.0, 5.0, 7.0 and 9.0 millimeters from the archwire bilaterally to simulate the en masse retraction of the anterior teeth. Power arms which were made from stainless steel wire were bonded to the archwire between the lateral incisors and the canines. Thirdly, orthodontic forces were applied from the mini-screws to the power arms. A line joining the mini-screw with the power arm was the line of action of the force. According to clinical cases, the magnitude of the orthodontic force was assumed to be 2.0 N (200 grams). In order to change the force direction, the length of the power arms was varied from 3.0, 5.0, 7.0 and 9.0 millimeters. The incisal edge and apex changes of maxillary central incisor were calculated and compared to each force direction. The results were divided into two parts: non-adjusted base of brackets model or non-straight wire model and adjusted base of brackets model which caused archwire be straightened. In non-adjusted base of brackets model or non-straight wire model, wire was not straight and did not afford for teeth movement. High stress occurred in cervical of maxillary lateral incisor, maxillary first molar and buccal of maxillary of second molar. Crown of maxillary lateral incisor displaced more than the other teeth. In periodontal ligament, the highest strain occurred nearly the cervical of maxillary lateral incisor. In adjusted base of brackets model or straight wire model, wire was straight and afforded for teeth movement like the teeth which have been leveled and aligned already. High stress occurred in cervical of maxillary lateral incisor, maxillary first molar, maxillary canine, maxillary second premolar and buccal of maxillary of second molar. Crown of maxillary lateral incisor displaced more than the other teeth. In periodontal ligament, the highest strain occurred nearly the cervical of maxillary lateral incisor. The incisal edge and apex changes of maxillary central incisor were calculated and compared for each force direction. In two simulated models, 3.0 millimeters of mini-screws and 9.0 millimeters of power arm showed the least differential change or nearly zero of the incisal edge and apex. However, the differential change of the incisal edge and apex in adjusted base of brackets model or straight wire model was only minus value. That means while incisal edge of maxillary central incisor moved linqually in upper anterior teeth retraction, apex of maxillary central incisor moved more labially. The next order which had the least change or nearly zero in adjusted base of bracket model was 9.0 millimeters of mini-screws and 9.0 millimeters of lever arm in adjusted base of bracket model or straight wire model. So during the simulation, 9.0 millimeters mini-screw and 9.0 millimeters lever arm was the force direction which bodily movement nearly to be occurred. The maxillary lateral incisor was protruded and more protruded in adjusted base of brackets model or straight wire model than non-adjusted base of brackets model or non-straight wire model. It might be hardly movement of adjacent teeth that limited maxillary lateral incisor movement of non-adjusted base of brackets model or non-straight wire model. In clinical application, less crowding and fair aligned teeth can be applied anterior retraction force, and there is less protrude of maxillary lateral incisor than well aligned teeth. However, periodontal strain in adjusted base of brackets model or straight wire model is greater than non-adjusted base of brackets model or nonstraight wire model, which risk or induce to occur root resorbed in these area

Thammasat University. Thammasat University Library

Address: BANGKOK

Email: preserv@tu.ac.th

Name: Nongluck Charoenworaluck

Role: advisor

Name: Vitoon Uthaisangsuk

Role: co-advisor

Created: 2015

Modified: 2021-10-27

Issued: 2021-10-27

วิทยานิพนธ์/Thesis

application/pdf

DOI: 10.14457/TU.the.2015.1547

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Oral Health Science

Grantor: Thammasat University

©copyrights Thammasat University

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