Effect of attachment configuration and trim line design on the force system of orthodontic aligners: A finite element study on the upper central incisor

Tarek M Elshazly; Christoph Bourauel; Mostafa Aldesoki; Damiano Salvatori; Abdulaziz Alhotan; Ludger Keilig; Ahmed Ghoneima

doi:10.1111/ocr.12779

Effect of attachment configuration and trim line design on the force system of orthodontic aligners: A finite element study on the upper central incisor

Orthod Craniofac Res. 2024 Mar 9. doi: 10.1111/ocr.12779. Online ahead of print.

Authors

Tarek M Elshazly^{1

2}, Christoph Bourauel¹, Mostafa Aldesoki¹, Damiano Salvatori³, Abdulaziz Alhotan⁴, Ludger Keilig^{1

5}, Ahmed Ghoneima²

Affiliations

¹ Oral Technology, Dental School, University Hospital Bonn, Bonn, Germany.
² Department of Orthodontics and Pediatric Dentistry, Hamdan Bin Mohammed College of Dental Medicine (HBMCDM), Mohammed Bin Rashid University of Medicine and Health Sciences (MBRU), Dubai, United Arab Emirates.
³ Institut Straumann AG, Basel, Switzerland.
⁴ Department of Dental Health, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia.
⁵ Department of Dental Prosthetics, Propaedeutics and Materials Science, Dental School, University Hospital Bonn, Bonn, Germany.

PMID: 38459802
DOI: 10.1111/ocr.12779

Abstract

Objectives: To use the finite element method (FEM) to investigate the effect of various attachment configurations and trimming line designs of orthodontic aligners on their biomechanical performance.

Method: A 3D upper jaw model was imported into 3D design software. The upper right central incisor tooth (Tooth 11) was made mobile, and its periodontal ligament (PDL) and bone structures were designed. Aligners were modelled with three distinct attachment configurations: No attachment, rectangular horizontal, rectangular vertical, and two trimming line designs; scalloped and straight extended, with a homogeneous thickness of 0.6 mm. These models were then imported into an FE software. Simulations were conducted for three different movements, including facial translation, distalization, and extrusion.

Results: Forces were recorded at 1.3-2.6 N during facial translation, 1.4-5.9 N in distalization, and 0.0-2.0 N in extrusion. The straight extended trimming line consistently generated higher forces than the scalloped design. Attachments had no significant impact on force components during facial translation but were more effective in distalization and extrusion. The combination of a straight extended trimming line with horizontal attachments exhibited the least stresses at the apical third during distalization, and the highest stresses during extrusion, suggesting superior retention.

Conclusions: Rectangular attachments offer limited benefits in facial translation, but horizontal rectangular attachments can intensify load in distalization and are crucial for force generation in extrusion. Horizontal attachments are preferred over vertical options. Additionally, the straight extended trim line enhances control of tooth movement and can replace attachments in certain cases.

Clinical relevance: These findings provide biomechanical evidence and an optimal protocol to guide clinical practice in planning diverse teeth movements. The emphasis is on the influence of attachment utilization and the specific design of aligner trimming lines to enhance control over tooth movement.

Keywords: biomechanics; orthodontic force; removable thermoplastic appliance; stress analysis; tooth movement.