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Research Papers

Tensile Properties of the Mandibular Condylar Cartilage

[+] Author and Article Information
M. Singh

Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045

M. S. Detamore

Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045detamore@ku.edu

1

Corresponding author.

J Biomech Eng 130(1), 011009 (Feb 07, 2008) (7 pages) doi:10.1115/1.2838062 History: Received January 29, 2007; Revised June 08, 2007; Published February 07, 2008

Mandibular condylar cartilage plays a crucial role in temporomandibular joint (TMJ) function, which includes facilitating articulation with the temporomandibular joint disc and reducing loads on the underlying bone. The cartilage experiences considerable tensile forces due to direct compression and shear. However, only scarce information is available about its tensile properties. The present study aims to quantify the biomechanical characteristics of the mandibular condylar cartilage to aid future three-dimensional finite element modeling and tissue engineering studies. Porcine condylar cartilage was tested under uniaxial tension in two directions, anteroposterior and mediolateral, with three regions per direction. Stress relaxation behavior was modeled using the Kelvin model and a second-order generalized Kelvin model, and collagen fiber orientation was determined by polarized light microscopy. The stress relaxation behavior of the tissue was biexponential in nature. The tissue exhibited greater stiffness in the anteroposterior direction than in the mediolateral direction as reflected by higher Young’s (2.4 times), instantaneous (1.9 times), and relaxed (1.9 times) moduli. No significant differences were observed among the regional properties in either direction. The predominantly anteroposterior macroscopic fiber orientation in the fibrous zone of condylar cartilage correlated well with the biomechanical findings. The condylar cartilage appears to be less stiff and less anisotropic under tension than the anatomically and functionally related TMJ disc. The anisotropy of the condylar cartilage, as evidenced by tensile behavior and collagen fiber orientation, suggests that the shear environment of the TMJ exposes the condylar cartilage to predominantly but not exclusively anteroposterior loading.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Posterior view of a left porcine condyle with the articular condylar cartilage intact. (b) An enlarged superior view of condylar cartilage isolated from a right porcine condyle, displaying the different regions of the cartilage: anterior, posterior, superior, medial, and lateral.

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Figure 2

A superior view of condylar cartilage superimposed with the specimen preparation scheme. Three specimens from each condylar cartilage were tested, either in the mediolateral direction or in the anteroposterior direction. In the mediolateral direction, specimens were prepared from the anterior, superior, and posterior regions. In the anteroposterior direction, specimens were prepared from the medial, central, and lateral regions.

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Figure 3

Photograph of the custom-built tensile bath and grip assembly. Shown here is the bath (1) to which the lower grip (2) was clamped. The upper grip (3) was attached to the movable crosshead that carried a load cell (4) of 50N capacity. The temperature was controlled using an immersion heater (5) and a temperature probe (6), both connected to a temperature controller.

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Figure 4

Typical stress-strain response of a condylar cartilage specimen, when stretched to 20% strain. The example curve provided here belonged to a specimen from the superior region, tested in the mediolateral direction. The curve demonstrates a nonlinear region extending to approximately 6% strain, followed by a linear region.

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Figure 5

Example of a typical stress relaxation response curve fitted to the linear viscoelastic models. The specimen provided here was from the superior region, tested in the mediolateral direction. The solid line represents the experimental data, showing the biexponential stress relaxation behavior of the specimen. The Kelvin model could not provide a close fit for the entire data. Therefore, the Kelvin model was fitted to only the slow relaxation phase and was used to obtain the equilibrium modulus. Using this equilibrium modulus, the second-order generalized Kelvin model provided a close fit to the experimental data.

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Figure 6

Polarized light micrographs displaying the collagen fibers from the fibrous zone of condylar cartilage from a right condyle at 100× magnification (scale bar=100μm). The locations from where the micrographs were captured are shown in the schematic of condylar cartilage in R1:C1 (denoted by white dots). The three columns (C2-4) correspond to tensile specimens tested in the anteroposterior direction and correspond to the specimens from the medial, central, and lateral regions, respectively. The three rows (R1-3) correspond to tensile specimens tested in the mediolateral direction, where the middle row (R2) corresponds to the specimens from the superior region of the cartilage, and other two rows (R1 and R3) belong to regions close to the anterior and posterior edges of the cartilage. Micrographs from the peripheral regions (R1, R3, C1, C5) show that fibers ran in a ring-like fashion around the periphery. Micrographs from the interior regions (R2:C2-4) show that fiber orientation was predominantly anteroposterior inside the periphery. A: anterior, P: posterior, M: medial, L: lateral.

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Figure 7

Superior view of a left porcine condyle superimposed with a simplified schematic of macroscopic fiber orientation of the fibrous zone, where only the predominant fiber orientation is shown. The schematic is based on the polarized light micrographs and visual inspection of the articular surface of the cartilage.

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