Εffect of cleansers on the composition and mechanical properties of orthodontic aligners in vitro

Anna Iliadi; Vera Enzler; Georgios Polychronis; Timo Peltomaki; Spiros Zinelis; Theodore Eliades

doi:10.1186/s40510-022-00449-w

Εffect of cleansers on the composition and mechanical properties of orthodontic aligners in vitro

Prog Orthod. 2022 Dec 15;23(1):54. doi: 10.1186/s40510-022-00449-w.

Authors

Anna Iliadi^#¹, Vera Enzler^#², Georgios Polychronis¹, Timo Peltomaki^{3

4

5}, Spiros Zinelis¹, Theodore Eliades⁶

Affiliations

¹ Department of Biomaterials, School of Dentistry, National and Kapodistrian University of Athens, Athens, Greece.
² Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Plattenstrasse 11, 8032, Zurich, Switzerland.
³ Department of Oral and Maxillofacial Diseases, Tampere University Hospital, Tampere, Finland Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland.
⁴ Department of Oral and Maxillofacial Diseases, Kuopio University Hospital, Kuopio, Finland.
⁵ Faculty of Health Sciences, Institute of Dentistry, University of Eastern Finland, Kuopio, Finland.
⁶ Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Plattenstrasse 11, 8032, Zurich, Switzerland. theodore.eliades@zzm.uzh.ch.

^# Contributed equally.

Abstract

Background: The aim of the study was to investigate the effect of three aligner cleaners on the composition and mechanical properties of two types of orthodontic aligners.

Materials and methods: The cleaners tested were two alkaline peroxide solutions (Retainer Brite-RB; Retainer Cleaner-RC) and one peroxide-free (Steraligner-ST) and the aligners Clear Aligner (C, polyester) and Invisalign (I, polyester-urethane). The aligners were immersed in the cleaner solutions as instructed every day (15 min for RB, RC; 5 min for ST) for a two-week period. The acidity of the solutions was tested with a pH meter. The changes in the chemical composition of the aligners were studied by attenuated total-reflection Fourier transform infrared spectrometry (ATR-FTIR), while Instrumented Indentation Testing (IIT) was used for assessment of changes in Martens Hardness (HM), modulus (E_IT), elastic index (n_IT) and relaxation (R_IT).

Results: RB and RC were weakly acidic (pH = 6.3), whereas ST was mildly acidic (pH = 4.8). The ATR-FTIR analysis demonstrated evidence of acidic hydrolysis of C in ST and I in RB. The IIT-derived properties of I were not affected by the cleaners. However, for C a significant change was found in HM (all cleaners), n_IT (all cleaners) and R_IT (RB, ST). Although the chemical changes support a hydrolytic material deterioration, the results of mechanical properties may interfere with the material residual stresses during fabrication.

Conclusions: Caution should be exerted in the selection of aligner cleaners. The mild acidic cleanser was more aggressive to the polyester, whereas an alkaline peroxide to the polyester-urethane aligner.

Keywords: Aligners; Chemical alterations; Cleansers; Mechanical properties.

MeSH terms

Hardness
Humans
Materials Testing
Orthodontic Appliances, Removable*
Polyesters
Urethane

Substances

Polyesters
Urethane