Korean J Orthod.  2018 Sep;48(5):316-325. 10.4041/kjod.2018.48.5.316.

Effects of thermoforming on the physical and mechanical properties of thermoplastic materials for transparent orthodontic aligners

• Ryu JH
• Kwon JS
• Jiang HB
• Cha JY
• Kim KM

• KMID: 2421316
• DOI: http://doi.org/10.4041/kjod.2018.48.5.316

Abstract

OBJECTIVE
The aim of this systematic multiscale analysis was to evaluate the effects of thermoforming on the physical and mechanical properties of thermoplastic materials used to fabricate transparent orthodontic aligners (TOAs).
METHODS
Specimens were fabricated using four types of thermoplastic materials with different thicknesses under a thermal vacuum. Transparency, water absorption and solubility, surface hardness, and the results of three-point bending and tensile tests were evaluated before and after thermoforming. Data were analyzed using one-way analysis of variance and Student's t-test.
RESULTS
After thermoforming, the transparency of Duran and Essix A+ decreased, while the water absorption ability of all materials; the water solubility of Duran, Essix A+, and Essix ACE; and the surface hardness of Duran and Essix A+ increased. The flexure modulus for the 0.5-mm-thick Duran, Essix A+, and eCligner specimens increased, whereas that for the 0.75-/1.0-mm-thick Duran and eClginer specimens decreased. In addition, the elastic modulus increased for the 0.5-mm-thick Essix A+ specimens and decreased for the 0.75-mm-thick Duran and Essix ACE and the 1.0-mm-thick Essix ACE specimens.
CONCLUSIONS
Our findings suggest that the physical and mechanical properties of thermoplastic materials used for the fabrication of TOAs should be evaluated after thermoforming in order to characterize their properties for clinical application.

Keyword

Thermoplastic materials; Physical properties; Mechanical properties; Aligner

MeSH Terms

Elastic Modulus
Hardness
Solubility
Vacuum
Water
Water

Figure

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  Figure 1 A, Thermoforming machine (Biostar®; Scheu Dental, Iserlohn, Germany) and fabrication of specimens for evaluation of the effects of thermoforming on the mechanical and physical properties of different thermoplastic materials with varying thicknesses. B, Surface X was cut from the models and used as a specimen for analysis.

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  Figure 2 Comparison of water absorption (A) and solubility (B) before thermoforming (BT) and after thermoforming (AT) and among different thermoplastic materials. All tests were performed for 1.0-mm-thick Duran, Essix A+, Essix ACE, and 0.75-mm-thick eCligner. The same capital letters indicate no difference between materials at the 1% significance level. The same lower case letters indicate no difference between BT and AT at the 1% significance level. See Table 1 for the manufacturer of each product.

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  Figure 3 Comparison of Knoop hardness values before thermoforming (BT) and after thermoforming (AT) and among different thermoplastic materials. All tests were performed for 1.0-mm-thick Duran, Essix A+, Essix ACE, and 0.75-mm-thick eCligner. The same capital letter indicates no difference between materials at the 1% significance level. The same lower case letters indicate no difference between BT and AT at the 1% significance level. See Table 1 for the manufacturer of each product.

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