Biomedical Engineering Reference
In-Depth Information
that is, relaxation of discal attachment, disc displacement, and disc perforation. The validated models
can be also used for studies of various clinical issues, such as the biomechanical effects of orthognathic
surgery, oral and maxillofacial surgery, oral implants, orthodontics, prosthodontics, and so on.
22.1 IntroduCtIon
The temporomandibular joints (TMJs), located between the condyle of the mandible and the articu-
lar fossa-eminence of the temporal bone, are unique joints in the jaw. The TMJs are the only bilat-
eral linked joints in the human body, and are necessary for chewing, swallowing, speech, and facial
expressions. Moreover, TMJs have been proven to be load-bearing joints and in remodeling all the
life. (Brehnan et al. 1981; Faulkner et al. 1987; Boyd et al. 1990; Throckmorton and Dechow 1994).
The joint loads produced by mandibular movement play an important role in the joints' structure
and function, and may be related to the etiology and treatment of TMJ disorders (Chen and Xu
1994; Chen et al. 1998; Tanaka et al. 2001a, 2004). Although some studies have measured TMJ
loads in vivo (Brehnan et al. 1981; Faulkner et al. 1987) and in vitro (Throckmorton and Dechow
1994), the stress distributions in these joints are still not well known because of the difficulties
in experimental measurements. The FE method has been largely used in dental biomechanics to
understand the stresses and the deformations in the normal mandibles (Hart et al. 1992; Korioth
and Hannam 1994a; Hu et al. 2003), to simulate the motions of the TMJ components (Chen and
Xu 1994; Devocht et al. 1996; Chen et al. 1998), to analyze the stress distribution in the two discs
and ligaments of each side during nonsymmetrical movements of a healthy joint (del Palomar and
Doblare 2006c), to analyze the differences in the stress distribution of the TMJ between subjects
with and without internal derangement (Tanaka et al. 2000, 2004; del Palomar and Doblare 2007),
and so on. The FE method has been proven to be a useful tool for evaluating the TMJ.
In the past three decades, many FE models of TMJs or mandibles have been constructed for
various biomechanical investigations. The articular surfaces of the condyle and the articular fossa-
eminence complex are covered with cartilage layers, which are separated by an articular disc. The
interaction between the cartilage layers and the disc is key for accurate simulation of the TMJ. The
disc and cartilage layers are bonded together in many mandibular models to analyze the stress dis-
tributions within the mandibles or the TMJs (Tanaka et al. 2000, 2001a; Hart et al. 1992; Korioth
and Hannam 1994a). In these models, the TMJs were treated as inactive joints that could not simu-
late the motions and the interactions of the joint components. Contact elements were introduced into
the two-dimensional (2D) FE models of the TMJ to simulate the interaction between the disc and
the articular surfaces (Chen and Xu 1994; Devocht et al. 1996; Chen et al. 1998). Similar research
using three-dimensional (3D) FE analyses has been reported (Tanaka et al. 2004; Beek et al. 2000,
2001). However, the single TMJ modeled in these studies failed to portray the linked characteristics
of the bilateral joints, and the load conditions were only applied through the condylar displacements.
Subsequently, contact elements were also used to simulate the upper and lower interfaces of the
discs in the 3D FE models of the mandible (Hu et al. 2003; del Palomar and Doblare 2006b, c, 2007;
Koolstra and van Eijden 2005). Gap elements have also been used to simulate the interfaces between
the articular disc and the cartilage layers in several FE models developed to analyze the stress dis-
tribution of the TMJs (Zhou et al. 1999; Castano et al. 2002). The normal behavior of the disc and
the articular surfaces could also be simulated using gap elements, whereas the tangential behavior
could not been simulated. Up to now, bond, gap, and contact elements have been used to simulate the
interaction between the disc and the articular cartilages. The type of modeling is very important in
order to obtain accurate results in stress analyses. The biomechanical environment in the TMJ is key
to understanding the origin and progression of TMD (Tanaka et al. 2004; del Palomar and Doblare
2007), so a verified model is also useful for clinical practice. Therefore, it is necessary to compare
the interaction in the TMJ with bond, contact, and gap elements (Liu et al. 2008).
TMD is the most common of TMJ diseases. The major symptoms of TMD are joint pain, abnor-
mal joint tone, and movement disorders of the mandible. TMD can be caused by many factors, such
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