Strain rate dependent orthotropic properties of pristine and impulsively loaded porcine temporomandibular joint disk
Section of Biomaterials, Department of Adult Restorative Dentistry, UNMC College of Dentistry, 40th and Holdrege Streets, Lincoln, Nebraska 68583-0750, USA. Journal of Biomedical Materials Research
10/2001; 57(1):25-34. DOI: 10.1002/1097-4636(200110)57:13.0.CO;2-H
The purpose of this study was to characterize the tensile stress-strain behavior of the porcine temporomandibular joint (TMJ) disk with respect to collagen orientation and strain rate dependency. The apparent elastic modulus, ultimate tensile strength, and strain at maximum stress were measured at three elongation rates (0.5, 50, and 500 mm/min) for dumbbell-shaped samples oriented along either anteroposterior or mediolateral axes of the disks. In order to study the effects of impact-induced fissuring on the mechanical behavior, the same properties were measured along each orientation at an elongation rate of 500 mm/min for disks subjected to impulsive loads of 0.5 N. s. The results suggested a strongly orthotropic nature to the healthy pristine disk. The values for the apparent modulus and ultimate strength were 10-fold higher along the anteroposterior axis (p < or = 0.01), which represented the primary orientation of the collagen fibers. Strain rate dependency was evident for loading along the anteroposterior axis but not along the mediolateral axis. No significant differences in any property were noted between pristine and impulsively loaded disks for either orientation (p > 0.05). The results demonstrated the importance of choosing an orthotropic model for the TMJ disk to conduct finite element modeling, to develop failure criteria, and to construct tissue-engineered replacements. Impact-induced fissuring requires further study to determine if the TMJ disk is orthotropic with respect to fatigue.
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- "Collagen fibers form a ring-like alignment around the periphery of the TMJ disc, with a strong anteroposterior alignment through the intermediate zone   . Correspondingly, the tensile strength and stiffness of specimens tested in the anteroposterior direction are an order of magnitude greater than those in the mediolateral direction   . The compressive stiffness of the disc is at least an order of magnitude less than the tensile stiffness , but still appears to be related to collagen. "
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ABSTRACT: Understanding structure-function relationships in the temporomandibular joint (TMJ) disc is a critical first step toward creating functional tissue replacements for the large population of patients suffering from TMJ disc disorders. While many of these relationships have been identified for the collagenous fraction of the disc, this same understanding is lacking for the next most abundant extracellular matrix component, sulfated glycosaminoglycans (GAGs). Though GAGs are known to play a major role in maintaining compressive integrity in GAG-rich tissues such as articular cartilage, their role in fibrocartilaginous tissues in which GAGs are much less abundant is not clearly defined. Therefore, this study investigates the contribution of GAGs to the regional viscoelastic compressive properties of the temporomandibular joint (TMJ) disc. Chondroitinase ABC (C-ABC) was used to deplete GAGs in five different disc regions, and the time course for >95% GAG removal was defined. The compressive properties of GAG depleted regional specimens were then compared to non-treated controls using an unconfined compression stress-relaxation test. Additionally, treated and non-treated specimens were assayed biochemically and histologically to confirm GAG removal. Compared to untreated controls, the only regions affected by GAG removal in terms of biomechanical properties were in the intermediate zone, the most GAG-rich portion of the disc. Without GAGs, all intermediate zone regions showed decreased tissue viscosity, and the intermediate zone lateral region also showed a 12.5% decrease in modulus of relaxation. However, in the anterior and posterior band regions, no change in compressive properties was observed following GAG depletion, though these regions showed the highest compressive properties overall. Although GAGs are not the major extracellular matrix molecule of the TMJ disc, they are responsible for some of the viscoelastic compressive properties of the tissue. Furthermore, the mechanical role of sulfated GAGs in the disc varies regionally in the tissue, and GAG abundance does not always correlate with higher compressive properties. Overall, this study found that sulfated GAGs are important to TMJ disc mechanics in the intermediate zone, an important finding for establishing design characteristics for future tissue engineering efforts.
Available from: Kyriacos Athanasiou
- "Previous biomechanical examinations have highlighted the TMJ disc's anisotropic and heterogeneous properties. Tensile strength and stiffness correlate with local collagen orientation, with greater values present in the central region when tested in the anteroposterior direction relative to the mediolateral direction (Shengyi and Xu, 1991; Beatty et al., 2001; Detamore and Athanasiou, 2003b). Compressive properties vary topographically; the relaxation modulus of the medial region is highest, while the posterior and anterior bands appear to support the highest instantaneous loads (del Pozo et al., 2002; Kim et al., 2003; Allen and Athanasiou, 2005, 2006a). "
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ABSTRACT: The temporomandibular joint (TMJ) disc plays a critical role in normal function of the joint, and many disorders of the TMJ are a result of disc dysfunction. Previous quantitative TMJ characterization studies examined either the human or a specific animal model, but no single study has compared different species, in the belief that differences in joint morphology, function, and diet would be reflected in the material properties of the disc. In this study, we examined topographical biochemical (collagen, glycosaminoglycan, and DNA content) and biomechanical (tensile and compressive) properties of the human TMJ disc, and also discs from the cow, goat, pig, and rabbit. Regional and interspecies variations were identified in all parameters measured, and certain disc characteristics were observed across all species, such as a weak intermediate zone under mediolateral tension. While human discs possessed properties distinct from those of the other species, pig discs were most similar to the human, suggesting that the pig may be a suitable animal model for TMJ bioengineering efforts.
Available from: David Marx
- "Although the high prevalence of disc displacement in otherwise asymptomatic adults has led some researchers to propose that it is a non-pathological variation of anatomy,19,20 disc displacement is absent mostly in the young, increases with time through adolescence and early adulthood, and thus precedes the precocious time-line of DJD in the TMJ.21–23 It has been postulated that the propensity to develop DJD of the TMJ depends on the health of the disc,22 which is anisotropic with respect to mechanical fatigue.24 "
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ABSTRACT: The likelihood of development of degenerative joint disease (DJD) of the temporomandibular joint (TMJ) is related to the integrity of the TMJ disc. Predilection for mechanical failure of the TMJ disc may reflect inter-individual differences in TMJ loads. Nine females and eight males in each of normal TMJ disc position and bilateral disc displacement diagnostic groups consented to participate in our study. Disc position was determined by bilateral magnetic resonance images of the joints. Three-dimensional (3D) anatomical geometry of each subject was used in a validated computer-assisted numerical model to calculate ipsilateral and contralateral TMJ loads for a range of biting positions (incisor, canine, molar) and angles (1-13). Each TMJ load was a resultant vector at the anterosuperi or-most mediolateral midpoint the condyle and characterized in terms of magnitude and 3D orientation. Analysis of variance (ANOVA) was used to test for effects of biting position and angle on TMJ loads. Mean TMJ loads in subjects with disc displacement were 9.5-69% higher than in subjects with normal disc position. During canine biting, TMJ loads in subjects with disc displacement were 43% (ipsilateral condyle, p=0.029) and 49% (contralateral condyle, p=0.015) higher on average than in subjects with normal disc position. Biting angle effects showed that laterally directed forces on the dentition produced ipsilateral joint loads, which on average were 69% higher (p=0.002) compared to individuals with normal TMJ disc position. The data reported here describe large differences in TMJ loads between individuals with disc displacement and normal disc position. The results support future investigations of inter-individual differences in joint mechanics as a variable in the development of DJD of the TMJ.
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