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Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie

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01-11-2019 | Aligner | Original Article

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

Authors: Benjamin A. Ihssen, Jan H. Willmann, Amr Nimer, Dieter Drescher

Published in: Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie | Issue 6/2019

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 (R_p02) 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 R_p02 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.

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Title: Effect of in vitro aging by water immersion and thermocycling on the mechanical properties of PETG aligner material
Authors: Benjamin A. Ihssen
Jan H. Willmann
Amr Nimer
Dieter Drescher
Publication date: 01-11-2019
Publisher: Springer Medizin
Keyword: Aligner
Published in: Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie / Issue 6/2019
Print ISSN: 1434-5293
Electronic ISSN: 1615-6714
DOI: https://doi.org/10.1007/s00056-019-00192-8

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Springer Medicine

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

Abstract

Purpose

Materials and methods

Results

Conclusions

Keynote webinar | Spotlight on medication adherence

Springer Medicine

Abstract

Purpose

Materials and methods

Results

Conclusions

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