Advertisement

Effect of in vitro aging by water immersion and thermocycling on the mechanical properties of PETG aligner material

  • Benjamin A. Ihssen
  • Jan H. WillmannEmail author
  • Amr Nimer
  • Dieter Drescher
Original Article
  • 78 Downloads

Abstract

Purpose

The mechanical properties of orthodontic aligners made from thermoplastic polymers decrease over time in the intraoral milieu. However, there is a lack of information on this topic in the literature. Thus, the elastic properties of polyethylene terephthalate glycol (PETG) aligner films were investigated in vitro under extreme temperature changes simulated by thermocycling, environmental temperature and water absorption.

Materials and methods

A total of 60 specimens made from PETG aligner films (CA Clear Aligner, Scheu Dental, Iserlohn, Germany) were divided into three groups (immersed in distilled water, subjected to accelerated ageing by thermocycling, control). These groups were again divided and tensile testing was performed for all groups at 22 and at 37 °C. Young’s modulus (E), 0.2% offset yield strength (Rp02) and ultimate tensile strength (UTS) were evaluated. Water absorption was determined using an analytical scale.

Results

All treated specimens showed water absorption, whereby specimens that were thermocycled absorbed 48% more water than the immersed ones. Young’s modulus and UTS were significantly lower for all three groups at 37 °C compared to the corresponding groups tested at 22 °C. Thermocycled and immersed groups showed a significantly lower Young’s modulus compared to the control group tested at the same temperature. The mean Rp02 was statistically different when comparing the control group tested at 22 °C to the one tested at 37 °C.

Conclusions

The results of this study add to the understanding of the clinically well-known degradation of orthodontic aligners during wear time. Extreme alternating temperatures along with warming up to intraoral temperature and water absorption can reduce the material’s Young’s modulus and may therefore promote a decrease of resulting orthodontic forces.

Keywords

Orthodontic tooth movement Elastic modulus Artificial ageing Tensile strength Mechanical phenomena 

Der Effekt von In-vitro-Alterung durch Thermozyklierung und Wasserimmersion auf die mechanischen Eigenschaften von PETG-Alignermaterial

Zusammenfassung

Ziel

Die mechanischen Eigenschaften von kieferorthopädischen Alignern aus thermoplastischen Polymeren unterliegen einer zeitabhängigen Degradation im intraoralen Milieu. Diesbezüglich bietet die aktuelle Literatur nur unzureichende und kontroverse Informationen. Insbesondere betrifft dies die Frage, inwieweit die Materialdegradation von extremen Temperaturwechseln und Wasseraufnahme abhängt. Die elastischen Eigenschaften von Polyethyleneterephthalate-Glycol(PETG)-Alignerfolien wurde in einem In-vitro-Setup untersucht, unter dem Einfluss von extremen intraoralen Temperaturwechseln, simuliert durch Thermozyklierung, Umgebungstemperatur und Wasserimmersion.

Material und Methoden

Insgesamt 60 Probekörper aus PETG-Alignerfolie (CA Clear Aligner, Scheu Dental, Iserlohn, Deutschland) wurden in 3 Gruppen geteilt (Immersion in destilliertem Wasser, beschleunigte Alterung durch Thermozyklieren, Kontrolle). Diese Gruppen wurden wieder unterteilt und alle Gruppen wurden Zugtests unterzogen, bei 22 und bei 37 °C. Für jede Gruppe wurden der Elastizitätsmodul, die 0,2 %-Dehngrenze sowie die nominelle Zugfestigkeit ermittelt. Die Wasserabsorption wurde mittels Analysewaage ermittelt.

Ergebnisse

Während alle behandelten Gruppen eine Wasseraufnahme zeigten, nahmen die thermozyklierten Probekörper im Mittel 48 % mehr Wasser auf als die in Wasser eingelegten. Alle 3 bei 37 °C getesteten Gruppen zeigten signifikant kleinere Elastizitätsmoduli und nominelle Zugfestigkeiten als ihre korrespondierenden bei 22 °C getesteten Gruppen. Die thermozyklierten und Immersionsgruppen hatten statistisch signifikant geringere Elastizitätsmoduli als die Kontrollgruppen, die bei gleicher Temperatur getestet wurden. Statistisch signifikant unterschiedlich war die mittlere 0,2 %-Dehngrenze nur beim Vergleich der bei 22 °C getesteten Kontrollgruppe mit der bei 37 °C getesteten Kontrollgruppe.

Schlussfolgerung

Die Ergebnisse dieser Studie tragen zum Verständnis der klinisch wohlbekannten Degradation von kieferorthopädischen Alignern während ihrer Tragezeit bei. Extreme wechselnde Temperaturen gemeinsam mit der Erwärmung auf Mundhöhlentemperatur und Wasserabsorption können den Elastizitätsmodul von PETG-Alignermaterial erniedrigen und deshalb einen Abfall orthodontischer Kräfte begünstigen.

Schlüsselwörter

Kieferorthopädische Zahnbewegung Elastizitätsmodul Künstliche Alterung Zugfestigkeit Mechanische Phänomene 

Notes

Funding

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors. Aligner raw material for specimen fabrication was provided by Scheu Dental, Iserlohn, Germany.

Compliance with ethical guidelines

Conflict of interest

B.A. Ihssen, J.H. Willmann, A. Nimer and D. Drescher declare that they have no competing interests.

Ethical standards

This article does not contain any studies with human participants or animals by any of the authors.

References

  1. 1.
    Ahn HW, Ha HR, Lim HN, Choi S (2015) Effects of aging procedures on the molecular, biochemical, morphological, and mechanical properties of vacuum-formed retainers. J Mech Behav Biomed Mater 51:356–366.  https://doi.org/10.1016/j.jmbbm.2015.07.026 CrossRefPubMedGoogle Scholar
  2. 2.
    Alexandropoulos A, Al Jabbari YS, Zinelis S, Eliades T (2015) Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials. Aust Orthod J 31(2):165–170PubMedGoogle Scholar
  3. 3.
    Arici S, Arici N (2003) Effects of thermocycling on the bond strength of a resin-modified glass ionomer cement: an in vitro comparative study. Angle Orthod 73(6):692–696.  https://doi.org/10.1043/0003-3219(2003)073 CrossRefPubMedGoogle Scholar
  4. 4.
    Barany TTC (2003) Effect of thermal ageing on fracture characteristics of an amorphous copolyester (PETG). Int J Polym Sci 31(1):381–385Google Scholar
  5. 5.
    Barany T, Földes E, Czigany T (2007) Effect of thermal and hygrothermal aging on plane stress toughness of ployethylene terephthylate sheets. Express Polym Lett 1(3):180–187CrossRefGoogle Scholar
  6. 6.
    Boubakri A, Elleuch K, Guermazi N, Ayedi HF (2009) Investigations on hygrothermal aging of thermoplastic polyurethane material. Mater Des 30(10):3958–3965.  https://doi.org/10.1016/j.matdes.2009.05.038 CrossRefGoogle Scholar
  7. 7.
    Brezniak N, Wasserstein A (2016) Orthodontic root resorption: a new perspective. Angle Orthod 86(6):1056–1057.  https://doi.org/10.2319/0003-3219-86.6.1056 CrossRefPubMedGoogle Scholar
  8. 8.
    Scheu-Dental GmbH (2019) CA Clear Aligner Treatment Process. https://www.ca-clear-aligner.com/b2c/index.html. Accessed 10 Mar 2019Google Scholar
  9. 9.
    Canbek K, Karbach M, Gottschalk F, Erbe C, Wehrbein H (2013) Evaluation of bovine and human teeth exposed to thermocycling for microleakage under bonded metal brackets. J Orofac Orthop 74(2):102–112.  https://doi.org/10.1007/s00056-012-0123-y CrossRefPubMedGoogle Scholar
  10. 10.
    Chen Y, Lin Z, Yang S (1998) Plasticization and crystallization of Polyethylne Tereptherlate induced by water. J Therm Anal Calorim 52:565–568CrossRefGoogle Scholar
  11. 11.
    Daub J, Berzins DW, Linn BJ, Bradley TG (2006) Bond strength of direct and indirect bonded brackets after thermocycling. Angle Orthod 76(2):295–300.  https://doi.org/10.1043/0003-3219(2006)076 CrossRefPubMedGoogle Scholar
  12. 12.
    De Abreu Neto HF, Costa AR, Correr AB et al (2015) Influence of light source, Thermocycling and Silane on the shear bond strength of metallic brackets to ceramic. Braz Dent J 26(6):685–688.  https://doi.org/10.1590/0103-6440201300416 CrossRefPubMedGoogle Scholar
  13. 13.
    de Almeida Pdel V, Gregio AM, Machado MA, de Lima AA, Azevedo LR (2008) Saliva composition and functions: a comprehensive review. J Contemp Dent Pract 9(3):72–80CrossRefGoogle Scholar
  14. 14.
    Dhakal HN, Zhang ZY, Richardson MOW (2007) Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites. Compos Sci Technol 67(7):1674–1683.  https://doi.org/10.1016/j.compscitech.2006.06.019 CrossRefGoogle Scholar
  15. 15.
    Deutsches Institut für Normung (2012) Kunststoffe – Bestimmung der Zugeigenschaften – Teil 1: Allgemeine Grundsätze (ISO 527-1:2012). Beuth Verlag GmbH, Berlin (Deutsche Fassung EN ISO 527-1:2012 (Polymers—Determination of tensile properties—Part 1: Gerneral principals (ISO 527-1:2012); German Version EN ISO 527-1:2012))Google Scholar
  16. 16.
    DIN Deutsches Istitut für Normung e. V. (2012) Kunststoffe – Bestimmung der Zugeigenschaften – Teil 2: Prüfbedingungen für Form- und Extrusionsmassen (ISO 527-2:2012). Beuth Verlag GmbH, Berlin (Deutsche Fassung EN ISO 527-2:2012 (Polymers—Determination of tensile properties—Part 2: Testing conditions for moulding and extrusion materials (ISO 527-2:2012); German version EN ISO 527-2:2012))Google Scholar
  17. 17.
    Dupaix RB, Boyce MC (2005) Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG). Polymer (Guildf) 46(13):4827–4838.  https://doi.org/10.1016/j.polymer.2005.03.083 CrossRefGoogle Scholar
  18. 18.
    Elhaddaoui R, Qoraich HS, Bahije L, Zaoui F (2017) Orthodontic aligners and root resorption: a systematic review. Int Orthod 15(1):1–12.  https://doi.org/10.1016/j.ortho.2016.12.019 CrossRefPubMedGoogle Scholar
  19. 19.
    Eliades T, Bourauel C (2005) Intraoral aging of orthodontic materials: the picture we miss and its clinical relevance. Am J Orthod Dentofacial Orthop 127(4):403–412.  https://doi.org/10.1016/j.ajodo.2004.09.015 CrossRefPubMedGoogle Scholar
  20. 20.
    Elkholy F, Panchaphongsaphak T, Kilic F, Schmidt F, Lapatki BG (2015) Forces and moments delivered by PET‑G aligners to an upper central incisor for labial and palatal translation. J Orofac Orthop 76(6):460–475.  https://doi.org/10.1007/s00056-015-0307-3 CrossRefPubMedGoogle Scholar
  21. 21.
    Elkholy F, Schmidt F, Jager R, Lapatki BG (2016) Forces and moments delivered by novel, thinner PET‑G aligners during labiopalatal bodily movement of a maxillary central incisor: an in vitro study. Angle Orthod 86(6):883–890.  https://doi.org/10.2319/011316-37r.1 CrossRefPubMedGoogle Scholar
  22. 22.
    Fang D, Zhang N, Chen H, Bai Y (2013) Dynamic stress relaxation of orthodontic thermoplastic materials in a simulated oral environment. Dent Mater J 32(6):946–951CrossRefGoogle Scholar
  23. 23.
    Gale MS, Darvell BW (1999) Thermal cycling procedures for laboratory testing of dental restorations. J Dent 27(2):89–99CrossRefGoogle Scholar
  24. 24.
    Gay G, Ravera S, Castroflorio T et al (2017) Root resorption during orthodontic treatment with Invisalign(R): a radiometric study. Prog Orthod 18(1):12.  https://doi.org/10.1186/s40510-017-0166-0 CrossRefPubMedPubMedCentralGoogle Scholar
  25. 25.
    Gomez JP, Pena FM, Martinez V, Giraldo DC, Cardona CI (2015) Initial force systems during bodily tooth movement with plastic aligners and composite attachments: a three-dimensional finite element analysis. Angle Orthod 85(3):454–460.  https://doi.org/10.2319/050714-330.1 CrossRefPubMedGoogle Scholar
  26. 26.
    Goracci C, Margvelashvili M, Giovannetti A, Vichi A, Ferrari M (2013) Shear bond strength of orthodontic brackets bonded with a new self-adhering flowable resin composite. Clin Oral Investig 17(2):609–617.  https://doi.org/10.1007/s00784-012-0729-x CrossRefPubMedGoogle Scholar
  27. 27.
    Hahn W, Dathe H, Fialka-Fricke J et al (2009) Influence of thermoplastic appliance thickness on the magnitude of force delivered to a maxillary central incisor during tipping. Am J Orthod Dentofacial Orthop 136(1):12 e11–12 e17.  https://doi.org/10.1016/j.ajodo.2008.12.015 (discussion 12–13)CrossRefGoogle Scholar
  28. 28.
    Hahn W, Engelke B, Jung K et al (2010) Initial forces and moments delivered by removable thermoplastic appliances during rotation of an upper central incisor. Angle Orthod 80(2):239–246.  https://doi.org/10.2319/033009-181.1 CrossRefPubMedGoogle Scholar
  29. 29.
    Hahn W, Zapf A, Dathe H et al (2010) Torquing an upper central incisor with aligners—acting forces and biomechanical principles. Eur J Orthod 32(6):607–613.  https://doi.org/10.1093/ejo/cjq007 CrossRefPubMedGoogle Scholar
  30. 30.
    Hussein M (2018) Effects of strain rate and temperature on the mechanical behavior of carbon black reinforced elastomers based on butyl rubber and high molecular weight polyethylene. Results Phys 9:511–517.  https://doi.org/10.1016/j.rinp.2018.02.043 CrossRefGoogle Scholar
  31. 31.
    ISO International Organization for Standardization (2015) ISO/TS 11405:2015 Dentistry—Testing of adhesion to tooth structure. ISO International Organization for Standardization, Geneva, SwitzerlandGoogle Scholar
  32. 32.
    Kattan M, Dargent E, Ledru J, Grenet J (2001) Strain-induced crystallization in uniaxially drawn PETG plates. J Appl Polym Sci 81(14):3405–3412.  https://doi.org/10.1002/app.1797 CrossRefGoogle Scholar
  33. 33.
    Kesling HD (1945) The philosophy of the tooth positioning appliance. Am J Orthod Dentofacial Orthop 31(6):297–304.  https://doi.org/10.1016/0096-6347(45)90101-3 CrossRefGoogle Scholar
  34. 34.
    Kohda N, Iijima M, Muguruma T, Brantley WA, Ahluwalia KS, Mizoguchi I (2013) Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances. Angle Orthod 83(3):476–483.  https://doi.org/10.2319/052512-432.1 CrossRefPubMedGoogle Scholar
  35. 35.
    Krishnan V, Davidovich Z (2015) Biological mechanisms of tooth movement vol 2. John Wiley & Sons, Ltd, Chichester, United KingdomCrossRefGoogle Scholar
  36. 36.
    Lombardo L, Martines E, Mazzanti V, Arreghini A, Mollica F, Siciliani G (2016) Stress relaxation properties of four orthodontic aligner materials: a 24-hour in vitro study. Angle Orthod.  https://doi.org/10.2319/113015-813.1 CrossRefPubMedGoogle Scholar
  37. 37.
    Nielsen LE, Landel RF (1994) Mechanical properties of polymers and composites, 2nd edn. Marcel Dekkar, Inc., New York.Google Scholar
  38. 38.
  39. 39.
    Align Technology, Inc. (2018) Q4 and 2017 Corporate Fact Sheet. http://www.aligntech.com/documents/Align%20Technology%20Corp%20Fact%20Sheet%202017%20Q4F.pdf. Accessed 9 Feb 2018Google Scholar
  40. 40.
    Align Technology Inc. (2019) Q4 and 2018 Corporate Fact Sheet. http://www.aligntech.com/documents/Align%20Technology%20Corp%20Fact%20Sheet%202018%20Q4.pdf. Accessed 3 Mar 2019Google Scholar
  41. 41.
    Richeton J, Ahzi S, Vecchio KS, Jiang FC, Adharapurapu RR (2006) Influence of temperature and strain rate on the mechanical behavior of three amorphous polymers: characterization and modeling of the compressive yield stress. Int J Solids Struct 43(7):2318–2335.  https://doi.org/10.1016/j.ijsolstr.2005.06.040 CrossRefGoogle Scholar
  42. 42.
    Richter C, Jost-Brinkmann PG (2015) Shear bond strength of different adhesives tested in accordance with DIN 13990-1/-2 and using various methods of enamel conditioning. J Orofac Orthop 76(2):175–187.  https://doi.org/10.1007/s00056-014-0281-1 CrossRefPubMedGoogle Scholar
  43. 43.
    Roylance D (2008) Mechanical properties of materials. MIT Massachusetts Institute of Technology, Massachusetts, USAGoogle Scholar
  44. 44.
    Ryokawa H, Miyazaki Y, Fujishima A, Miyazaki T, Maki K (2006) The mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Orthod Waves 65(2):64–72.  https://doi.org/10.1016/j.odw.2006.03.003 CrossRefGoogle Scholar
  45. 45.
    Schubert MA, Wiggins MJ, Schaefer MP, Hiltner A, Anderson JM (1995) Oxidative biodegradation mechanisms of biaxially strained poly(etherurethane urea) elastomers. J Biomed Mater Res 29(3):337–347.  https://doi.org/10.1002/jbm.820290309 CrossRefPubMedGoogle Scholar
  46. 46.
    Sheibaninia A (2014) Effect of thermocycling on nickel release from orthodontic arch wires: an in vitro study. Biol Trace Elem Res 162(1–3):353–359.  https://doi.org/10.1007/s12011-014-0136-z CrossRefPubMedGoogle Scholar
  47. 47.
    Simon M, Keilig L, Schwarze J, Jung BA, Bourauel C (2014) Forces and moments generated by removable thermoplastic aligners: incisor torque, premolar derotation, and molar distalization. Am J Orthod Dentofacial Orthop 145(6):728–736.  https://doi.org/10.1016/j.ajodo.2014.03.015 CrossRefPubMedGoogle Scholar
  48. 48.
    Sokucu O, Siso SH, Ozturk F, Nalcaci R (2010) Shear bond strength of orthodontic brackets cured with different light sources under Thermocycling. Eur J Dent 4(3):257–262CrossRefGoogle Scholar
  49. 49.
    Zachrisson YO, Zachrisson BU, Buyukyilmaz T (1996) Surface preparation for orthodontic bonding to porcelain. Am J Orthod Dentofacial Orthop 109(4):420–430CrossRefGoogle Scholar

Copyright information

© Springer Medizin Verlag GmbH, ein Teil von Springer Nature 2019

Authors and Affiliations

  1. 1.Department of OrthodonticsUniversity of DuesseldorfDuesseldorfGermany
  2. 2.Division of SurgeryImperial College LondonLondonUK

Personalised recommendations