Korean J Orthod.  2010 Feb;40(1):16-26. 10.4041/kjod.2010.40.1.16.

The effect of thickness and deflection of orthodontic thermoplastic materials on its mechanical properties

• Min S
• Hwang CJ
• Yu HS
• Lee SB
• Cha JY

• KMID: 1975619
• DOI: http://doi.org/10.4041/kjod.2010.40.1.16

Abstract

OBJECTIVE
The purposes of this study were to evaluate the force and stress depending on the type, deflection and thickness of the materials and to evaluate the mechanical properties of thermoplastic materials after repeated loading.
METHODS
Four types of thermoplastic products were tested. Force until the deflections of 2.0 mm and the stress when the materials were restoring to its resting position were evaluated. The mechanical properties of thermoplastic materials evaluated after 5 repeated loading cycles.
RESULTS
The interaction was observed between the thickness and the deflection (p < 0.05) from the regression equation. Thickness and amount of deflection rather than products and materials showed the largest effect on force and stress. In all products, at least 159 gf of force was required for more than 1.0 mm deflection or when materials with 1.0 mm thickness were deflected. The stress recorded was more than 19 gf/mm2. During repeated loading, each group showed significant difference on the force and the stress p < 0.01), 10 - 17% reduction of force and 4 - 7% reduction of stress in average.
CONCLUSIONS
Proper thickness of thermoplastic materials and deflection level of tooth movement should be decided for the physiologic tooth movement. Force decay after repeated loading should be considered for the efficient tooth movement.

Keyword

Thermoplastic materials; Force; Stress; Repeated loading

MeSH Terms

Tooth Movement

Figure

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  Fig 1 Biostar® (Scheu-Dental, Iserlohn, Germany) and fabricated dental model.

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  Fig 2 Experimental procedure used in this study. A, Universal test machine, Instron®; B, schematic diagram of 3 point bending test.

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  Fig 3 Increase in bending force and recovery stress level depending on the thickness and amount of deflection for all four types of products (Lt, Force (gf); Rt, recovery stress (gf/mm2)).

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  Fig 4 Graph showing bending force and recovery stress changes after repeated loading (Lt, Force (gf); Rt, recovery stress (gf/mm2)).

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