Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials


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Australasian Orthodontic Journal

Australian Society of Orthodontists

Subject: Dentistry, Orthodontics & Medicine


ISSN: 2207-7472
eISSN: 2207-7480





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VOLUME 31 , ISSUE 2 (November 2015) > List of articles

Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials

Alexandros Alexandropoulos / Youssef S. Al Jabbari / Spiros Zinelis / Theodore Eliades *

Citation Information : Australasian Orthodontic Journal. Volume 31, Issue 2, Pages 165-170, DOI:

License : (CC BY 4.0)

Published Online: 15-August-2021



Aim: The aim of the present study was to characterise the chemical and mechanical properties of contemporary thermoplastic orthodontic materials.

Materials and methods: Four thermoplastic materials were tested: Clear Aligner (Scheu-Dental), ACE and A+ (Dentsply), and Invisalign (Align Technology). Eight appliances were fabricated from each material and a small portion from each was analysed by ATR-FTIR spectroscopy. The appliances were cut and, following metallographic grinding and polishing, were subjected to instrumented indentation testing (IIT) employing a Vickers indenter. Martens Hardness (HM), Indentation Modulus (EIT), Elastic to Total Work Ratio (elastic index (ηIT)) and Indentation Creep (CIT) were determined according to ISO 14577-1. The mean values of the mechanical properties were statistically analysed by one way ANOVA and Tukey Kramer multiple comparison test at a = 0.05.

Results: ATR-FTIR analysis identified that Invisalign was a polyurethane-based material, whereas the others were based on polyester, polyethylene glycol terephthalate (PETG). Invisalign showed higher hardness and modulus values, a slightly higher brittleness and lesser creep resistance compared with the PETG-based products.

Conclusions: The materials tested showed significant differences in their chemical structure and mechanical properties and therefore differences in their clinical behaviour are anticipated.

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1. Bergström K, Halling A, Wilde B. Orthodontic care from the patients’ perspective: perceptions of 27-year-olds. Eur J Orthod 1998;20:319-29.

2. Ziuchkovski JP, Fields HW, Johnston WM, Lindsey DT. Assessment of perceived orthodontic appliance attractiveness. Am J Orthod Dentofacial Orthop 2008;133:S68-78.

3. Walton DK, Fields HW, Johnston WM, Rosenstiel SF, Firestone AR, Christensen JC. Orthodontic appliance preferences of children and adolescents. Am J Orthod Dentofacial Orthop 2010;138:698 e1-12; discussion 698-9.

4. Rosvall MD, Fields HW, Ziuchkovski J, Rosenstiel SF, Johnston WM. Attractiveness, acceptability, and value of orthodontic appliances. Am J Orthod Dentofacial Orthop 2009;135:276 e1-12; discussion 276-7.

5. Kravitz ND, Kusnoto B, BeGole E, Obrez A, Agran B. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. Am J Orthod Dentofacial Orthop 2009;135:27-35.

6. Simon M, Keilig L, Schwarze J, Jung BA, Bourauel C. Treatment outcome and efficacy of an aligner technique—regarding incisor torque, premolar derotation and molar distalization. BMC Oral Health 2014;14:68.

7. Vardimon AD, Robbins D, Brosh T. In-vivo von Mises strains during Invisalign treatment. Am J Orthod Dentofacial Orthop 2010;138:399-409.

8. Simon M, Keilig L, Schwarze J, Jung BA, Bourauel C. Forces and moments generated by removable thermoplastic aligners: incisor torque, premolar derotation, and molar distalization. Am J Orthod Dentofacial Orthop 2014;145:728-36.

9. Hahn W, Engelke B, Jung K, Dathe H, Fialka-Fricke J, KubeinMeesenburg D et al. Initial forces and moments delivered by removable thermoplastic appliances during rotation of an upper central incisor. Angle Orthod 2010;80:239-46.

10. Hahn W, Dathe H, Fialka-Fricke J, Fricke-Zech S, Zapf A, KubeinMeesenburg D et al. Influence of thermoplastic appliance thickness on the magnitude of force delivered to a maxillary central incisor during tipping. Am J Orthod Dentofacial Orthop 2009;136:12 e1- 7; discussion 12-3.

11. Kohda N, Iijima M, Muguruma T, Brantley WA, Ahluwalia KS, Mizoguchi I. Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances. Angle Orthod 2013;83:476-83.

12. Clements KM, Bollen AM, Huang G, King G, Hujoel P, Ma T. Activation time and material stiffness of sequential removable orthodontic appliances. Part 2: Dental improvements. Am J Orthod Dentofacial Orthop 2003;124:502-8.

13. Fang D, Zhang N, Chen H, Bai Y. Dynamic stress relaxation of orthodontic thermoplastic materials in a simulated oral environment. Dent Mater J 2013;32:946-51.

14. International Organization for Standardization. Metallic materials – Instrumented indentation test for hardness and materials parameters. ISO14577-1. Geneva: ISO, 2002.

15. Gracco A, Mazzoli A, Favoni O, Conti C, Ferraris P, Tosi G et al. Short-term chemical and physical changes in invisalign appliances. Aust Orthod J 2009;25:34-40.

16. Gardner GD, Dunn WJ, Taloumis L. Wear comparison of thermoplastic materials used for orthodontic retainers. Am J Orthod Dentofacial Orthop 2003;124:294-7.

17. Ryokawa H, Miyazaki Y, Fujishima A, Miyazaki T, Maki K. The mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Orthodontic Waves 2006;65:64-72.

18. Pascual AL, Beeman CS, Hicks EP, Bush HM, Mitchell RJ. The essential work of fracture of thermoplastic orthodontic retainer materials. Angle Orthod 2010;80:554-61.

19. Kwon JS, Lee YK, Lim BS, Lim YK. Force delivery properties of thermoplastic orthodontic materials. Am J Orthod Dentofacial Orthop 2008;133:228-34; quiz 328 e1.

20. Shahdad SA, McCabe JF, Bull S, Rusby S, Wassell RW. Hardness measured with traditional Vickers and Martens hardness methods. Dent Mater 2007;23:1079-85.