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Dynamic Properties of Bovine Temporomandibular Joint Disks Change with Age

Department of Orthodontics, Hiroshima University Faculty of Dentistry, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan;
¹ Division of Mechanical Science, Department of Systems and Human Science, Osaka University School of Engineering Science;
² Department of Prosthetic Dentistry, Hiroshima University Faculty of Dentistry;

View larger version (19K): [in this window] [in a new window]   Figure 1. Block diagram of the dynamic viscoelastometer with a schematic representation of the relationship between stress and strain of a viscoelastic material (A), and an illustration showing the anatomy of the bovine TMJ disc and the location of the specimen dissected (B). The sinusoidal strain is produced by a tension control motor in the driver, and the stress and strain are measured by means of load and displacement detectors and transmitted to a data processor. In a viscoelastic material, the phase difference between stress and strain is somewhere between (/2 > > 0), and the complex modulus E* is resolved into two components, i.e., the storage modulus E' and the loss modulus E'', shown vectorially. Furthermore, the tangent of the phase angle () between stress and strain is a measure of the ratio of energy loss to energy stored during cyclic deformation.

View larger version (24K): [in this window] [in a new window]   Figure 2. The complex modulus |E*|, storage modulus E', and loss modulus E'' as a function of frequency in the young-adult (A), the adult (B), and the mature-adult groups (C). Error bars are standard deviations (for each group, n = 12). The frequency has a proportional effect on the values of the moduli. Complex modulus |E*|; x Storage modulus E'; and • Loss modulus E''.

View larger version (22K): [in this window] [in a new window]   Figure 3. Loss tangent vs. frequency. Error bars are standard deviations. Young-adult, Adult, and • Mature-adult groups.

View larger version (19K): [in this window] [in a new window]   Figure 4. Means and standard deviations of storage modulus E' and loss modulus E'' (A), and loss tangent tan (B) at 1.0 Hz. Asterisks: significance of differences among the groups (** p < 0.01) as tested with Student’s t test. The mature-adult group had significantly larger moduli than the younger groups.

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