Biomedical Engineering Reference
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as abnormal occlusion, joint trauma, bad habits (bruxism, clenching, unilateral chewing, etc.), loss of
posterior teeth, and psychological factors. Except for masticatory muscle disorders, TMD is related
to abnormal positioning between the disc and facies articularis of the condyle and articular fossa,
such as occurence with disc displacements, relaxation of discal attachment, and disc perforation.
TMD may be caused by abnormal loads in the TMJ. On the other hand, TMD could also lead
to abnormal stress distributions in the TMJ. Tanaka et al. evaluated the differences in stress dis-
tribution in the TMJ for models with and without anterior disc displacement during maximum
occlusion (2000) and jaw opening (2004). They also analyzed the regularity of stress distribution
in the TMJ during prolonged clenching and found that the maximum stress was located in the cen-
tral and lateral zones of the disc (Tanaka et al. 2008). del Palomar and Doblare (2007) simulated
anteriorly displaced discs with and without reduction during jaw opening. The results showed that
anterior displacement of the disc could lead to greater compressive stress in the posterior band of
the disc. They also compared the displacements and stress distributions of an anteriorly displaced
disc without reduction and a surgically repositioned one with those of a healthy disc during jaw
opening (del Palomar and Doblare 2006a). Roh et al. (2012) used MRI scans to study the relation-
ships between anterior disc displacement, joint effusion, and degenerative changes of the TMJ with
TMD. The results showed that anterior disc displacement was significantly related to degenerative
changes of the condyles and joint effusions in patients with TMD. Koolstra (2012) analyzed the
influence of friction on anterior disc displacement, and suggested that an increase in friction may
not be the cause of anterior disc displacement. These studies of TMD were focused on anterior disc
displacement. Other types of TMD should also be investigated, for example other directions of disc
displacements, relaxation of discal attachment, and disc perforation.
In this chapter, a 3D FE model of the human mandible, disc, and fossa-eminence complex was
developed based on CT images. The mandibular ligaments and the attachments of the discs were
considered. Bond, gap, and contact elements were used to simulate the interaction between the discs
and the cartilages in the TMJs. Differences between the three simulations were compared with the
stress analyses of the models under centric occlusion. Then the effects of different occlusal loads
(i.e., centric occlusion, anterior occlusion, and right side molar occlusion) on the stress distributions
in TMJ were analyzed. FE models of three types of TMD were developed: relaxation of discal
attachment (relaxation of anterior and posterior attachments), disc displacement (anterior, posterior,
medial, and lateral disc displacement), and disc perforation. The stress distributions in TMJs were
compared with a healthy TMJ.
22.2
ComParatIve reSearCh oF tmJ SImulatIonS
22.2.1
d
eVelopment
of
a
m
andiBle
and
tmJ m
odel
22.2.1.1 Finite element modeling
The geometry of the model was based on CT images of a volunteer with normal occlusion and
asymptomatic joints. The contours of the cortical and cancellous bone were digitized and imported
into ANSYS 8.0 (Swanson Analysis System Co., Houston, TX) for constructing the 3D model of
the mandible and the articular fossa-eminence complex. The teeth and periodontal tissues have
been shown to have little influence on the stress distribution in the mandible, far from the alveolar
bone (Hart et al. 1992). Because this study focused on simulations of the TMJs, the teeth were not
included in the models. Fibrocartilage layers were simulated on the articular surfaces of the con-
dyle and the temporal bone. Based on the anatomical structure, the thickness of the cartilage layers
varied from 0.2 mm at the crests of the condyle and the articular fossa to 0.5 mm at the anterior
surfaces of the condyle and the articular eminence (Pullinger et al. 1990). According to the shapes
of the articular surfaces and the anatomy of the disc (Hansson and Nordstrom 1977), the models
of the two articular discs were constructed with an anterior band of 2 mm, an intermediate zone of
1 mm, and a posterior band of 2.7 mm, as shown in Figure 22.1.
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