Semester

Spring

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Osama Mukdadi

Committee Co-Chair

Peter Ngan

Committee Member

Khaled Alsharif

Committee Member

Terence Musho

Abstract

Clear aligners have emerged as the most popular and preferred method of treatment for patients with orthodontic malocclusions. This is greatly due to the comfort and aesthetically appealing factors when compared to fixed appliances . Clear aligners are either thermoformed or 3D direct-printed plastics that apply biomechanical forces to the surface of teeth to trigger tooth movement and bone remodeling process. Common Class I malocclusions with mild or moderate crowding can be treated with clear aligners alone. However, treatment of Class II and Class III malocclusions that require extraction of permanent teeth or correction of severe rotations, and teeth extrusions will require attachments and ancillary tools . To improve treatment efficacy, attachments are placed on the tooth surface to provide precise force application. Attachments are essentially small composite resin structures that can vary in shape and size to assist specific tooth movement. Finite element analysis provides a means to develop pre-operative methods to elucidate the efficacy of novel clear aligner treatments and validate their clinical relevance. This study aims to investigate the biomechanical responses of the teeth and corresponding anatomical structures in a multitude of common treatment scenarios. An anatomically detailed 3D reconstruction of human maxillary structure was developed, including teeth, periodontal ligaments, cortical bone, and trabecular bone. The 3D model was constructed through segmentation using multiple software packages such as 3D Slicer, Autodesk Meshmixer, and ANSYS SpaceClaim. Multiple finite element models were developed to investigate multiple clinical variables such as attachment shape, size, and aligner material selection utilizing ANSYS Mechanical software. The first study focused on the effect of the attachment shapes (flat: square, rectangle, trapezoid, and curved: ellipse, semicircle) on single molar movements, such as mesialization, extrusion, intrusion, and rotation. The effects of attachment shape and placement of tooth surface were studied on the mesialization of maxillary molars. Results showed that attachment placement on the buccal and lingual surfaces of the first molar demonstrated better control over tooth movements, incurring less tipping during mesialization and rotation. Flat attachments produced about 18% more displacement than curved attachments on average for all four types of tooth movements. This is due to having more surface area, but excess mesial tipping and anchorage loss were noted. The second study examined the effect of attachment size and shape during a space-closure treatment post the first premolar extraction. Results revealed that increasing attachments length from 2 mm to 5 mm may improve force application and increase displacement in the crown and root but may contribute to high strains in the periodontal ligaments (PDLs). The rate of effective movement in the desired direction for the canine, 2nd premolar, and 1st molar are 40%, 25%, and 17% on average, respectively. The third study elucidated the performance of different aligner materials on space-closure. Aligner materials simulated included thermoplastic polyurethane, Tera Harz, polycarbonate, and polyethylene terephthalate glycol. Results indicated that polycarbonate and polyethylene terephthalate glycol transmitted higher forces due to their high rigidity. The rigid plastics translated the crowns by about 60% more than thermoplastic polyurethane and Tera Harz. These findings provide a better understanding of the relevancy of clear aligner biomechanics along with key insight to clinicals for optimal attachment selection and placement coinciding with aligner material selection.

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