Effect of material composition and thickness of orthodontic aligners on the transmission and distribution of forces: an in vitro study

Tarek M Elshazly; Christoph Bourauel; Ahmed Ismail; Omar Ghoraba; Mostafa Aldesoki; Damiano Salvatori; Hanaa Elattar; Abdulaziz Alhotan; Yasmine Alkabani

doi:10.1007/s00784-024-05662-x

Effect of material composition and thickness of orthodontic aligners on the transmission and distribution of forces: an in vitro study

Clin Oral Investig. 2024 Apr 19;28(5):258. doi: 10.1007/s00784-024-05662-x.

Authors

Tarek M Elshazly¹, Christoph Bourauel², Ahmed Ismail^{2

3}, Omar Ghoraba², Mostafa Aldesoki², Damiano Salvatori⁴, Hanaa Elattar⁵, Abdulaziz Alhotan⁶, Yasmine Alkabani⁷

Affiliations

¹ Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany. tarek.m.elshazly@gmail.com.
² Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany.
³ Biomaterials Department, Faculty of Dentistry, Ain Shams University, Cairo, Egypt.
⁴ Institut Straumann AG, Basel, Switzerland.
⁵ Orthodontic Department, Faculty of Dentistry, Suez Canal University, Ismailia, Egypt.
⁶ Department of Dental Health, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia.
⁷ Oral and Dental Research Institute, National Research Centre, Giza, Egypt.

Abstract

Objectives: To investigate the effects of material type and thickness on force generation and distribution by aligners.

Materials and methods: Sixty aligners were divided into six groups (n = 10): one group with a thickness of 0.89 mm using Zendura Viva (Multi-layer), four groups with a thickness of 0.75 mm using Zendura FLX (Multi-layer), CA Pro (Multi-layer), Zendura (Single-layer), and Duran (Single-layer) sheets, and one group with a thickness of 0.50 mm using Duran sheets. Force measurements were conducted using Fuji® pressure-sensitive films.

Results: The lowest force values, both active and passive, were recorded for the multi-layered sheets: CA Pro (83.1 N, 50.5 N), Zendura FLX (88.9 N, 60.7 N), and Zendura Viva (92.5 N, 68.5 N). Conversely, the highest values were recorded for the single-layered sheets: Duran (131.9 N, 71.8 N) and Zendura (149.7 N, 89.8 N). The highest force was recorded at the middle third of the aligner, followed by the incisal third, and then the cervical third. The net force between the incisal and cervical thirds (F_I-F_C) showed insignificant difference across different materials. However, when comparing the incisal and middle thirds, the net force (F_I-F_M) was higher with single-layered materials. Both overall force and net force (F_I-F_M) were significantly higher with 0.75 mm compared to those with a thickness of 0.50 mm.

Conclusions: Multi-layered aligner materials exert lower forces compared to their single-layered counterparts. Additionally, increased thickness in aligners results in enhanced retention and greater force generation. For effective bodily tooth movement, thicker and single-layered rigid materials are preferred.

Clinical relevance: This research provides valuable insights into the biomechanics of orthodontic aligners, which could have significant clinical implications for orthodontists. Orthodontists might use this information to more effectively tailor aligner treatments, considering the specific tooth movement required for each individual patient. In light of these findings, an exchangeable protocol for aligner treatment is suggested, which however needs to be proven clinically. This protocol proposes alternating between multi-layered and single-layered materials within the same treatment phase. This strategy is suggested to optimize treatment outcomes, particularly when planning for a bodily tooth movement.

Keywords: Biomechanics; Orthodontic force; Pressure sensitive film; Removable thermoplastic appliance; Stress analysis; Tooth movement.

MeSH terms

Biomechanical Phenomena
Humans
Orthodontic Appliance Design*
Tooth Movement Techniques* / methods
Treatment Outcome