Biomedical Engineering Reference
In-Depth Information
other pathological changes in the anterior and posterior bands could probably be induced by such
significantly high tensile stresses.
The maximum von Mises stresses of the condyle cartilages with anterior and posterior disc
displacements were approximately half as much as those in the base model, and the magnitudes
were close to the base model in models with medial and lateral disc displacements. However, the
stresses of the posterior articular eminences with various disc displacements were much greater
than those in the base model. The maximum von Mises stresses of the posterior articular emi-
nences with posterior and medial disc displacements were 59 and 46 times greater than the base
model, respectively. Moreover, the maximum tensile stress of the posterior articular eminences
occurred after posterior disc displacement and reached 5.08 MPa, significantly exceeding the
tensile failure stress (2.15 MPa) (Yi and Kang 2001). The significantly increased stresses in the
posterior articular eminence could cause flattening and perforation of the cartilage and possible
bone resorption.
In summary, various disc displacements could lead to an increase in stress in the discs and pos-
terior articular eminences, and the excessive stresses may lead to worse disc displacement. Intensive
disc displacements will also increase the magnitude of stresses and alter the stress distributions in
the TMJs. Therefore, an effective method to restore the normal position and function of the disc is
to treat TMD when initial symptoms are noticed, such as joint clicking.
22.4.2.3 disc Perforation
Similar to disc displacement, the interaction between the disc and the articular fossa-eminence was
much more intensive than that between the disc and the condyle in the model with disc perforation.
The maximum contact stresses occurred between the anterior condyle and the lower surface of the
intermediate zone of the disc and between the upper surface of the intermediate zone of the disc
and the posterior articular eminence, respectively. Therefore, the stress concentration was located
at the intermediate zone of the perforated disc (Figure 22.9). The stresses of all the bands of the
perforated disc were greater than the identical disc in the base model. The compressive stresses in
the anterior band of the perforated disc were much greater than the tensile stresses, inconsistent with
the tension-bearing structure. On the contrary, the posterior band of the perforated disc undertook
higher tensile stresses than compressive stresses, inconsistent with the pressure-bearing structure.
The maximum stress of the three bands of the perforated disc may not lead to continued perforation,
accordant with Stratmann's study (Stratmann and Schaarschmidt 1996). However, disc perforation
could lead to increased stress and unreasonable stress distribution, possibly inducing other patho-
logical changes to the perforated disc.
Max: 0.239MPa
Max:
0.615MPa
(a)
(b)
0
.02
.08
.2
.6
.01
.04
.1
.4
FIgure 22.9
(See color insert.)
The von Mises stress distributions of the normal and disc perforation
models (the maximum stresses were listed; units: MPa): (a) normal disc and (b) perforated disc.
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