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

Sam Min; Chung-Ju Hwang; Hyung-Seog Yu; Sang-Bae Lee; Jung-Yul Cha

doi:10.4041/kjod.2010.40.1.16

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Min, Hwang, Yu, Lee, and Cha: The effect of thickness and deflection of orthodontic thermoplastic materials on its mechanical properties

Original Article

Korean Journal of Orthodontics

Korean Journal of Orthodontics 2010; 40(1): 16-26.

Published online: 28 February 2010

DOI: https://doi.org/10.4041/kjod.2010.40.1.16

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

Sam Min, DDS, MSD^a, Chung-Ju Hwang, DDS, MSD, PhD^b, Hyung-Seog Yu, DDS, MSD, PhD^b, Sang-Bae Lee, DDS, MSD, PhD^c, Jung-Yul Cha, DDS, MSD, PhD^d

^aGraduate Student, Department of Orthodontics, College of Dentistry, Yonsei University, Korea.

^bProfessor, Department of Orthodontics, College of Dentistry, Oral Science Research Institute, The Institute of Cranio-facial Deformity, Yonsei University, Korea.

^cReseacher, Department of Dental Biomaterials and Bioengineering, College of Dentistry, Yonsei University, Korea.

^dAssistant Professor, Department of Orthodontics, College of Dentistry, Yonsei University, Korea.

Corresponding author: Jung-Yul Cha. Department of Orthodontics, College of Dentisty, Yonsei University, 134, Shinchon-dong, Seodaemun-gu, Seoul 120-752, Korea. +82 2 2228 3103; jungcha@yuhs.ac

Received 30 June 2009 Revised 31 December 2009 Accepted 3 January 2010

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.

Keywords: Thermoplastic materials, Force, Stress, Repeated loading

Figures and Tables

Fig 1

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

Fig 2

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

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)).

Fig 4

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

Table 1

Prescription of materials used in this study

Essix ACE does not provide 0.5 mm thickness sheets.

Table 2

Condition of thermoform used in this study

Table 3

Thickness differentiation after thermoform (Unit : mm)

SD, Standard deviation; ΔThickness, thickness differentiation after thermoform.

Table 4

Factors associated with bending force and recovery stress (top) and multiple regressions for interaction among products, thickness, and deflection rate (bottom)

DF, Degree of freedom; Sig, significant; NS, not significant; SE, standard error. ^*p < 0.001.

Table 5

Comparative mean force according to three thickness levels and four deflection levels for four types of products

SD, Standard deviation. ^*p < 0.05.

Table 6

Comparative mean recovery stress according to three thickness levels and four deflection rates for four types of products

SD, Standard deviation.

Notes

This study was supported by a faculty research grant of Yonsei University College of Dentistry for 2008 (6-2008-0058).

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