Martin A. Taubman, Editor
E. Tanaka1* and J.H. Koolstra2
of Orthodontics and Dentofacial Orthopedics, The University of Tokushima Graduate School of Oral Sciences, 3-18-15 Kuramoto-cho, Tokushima 770-8504, Japan; and 2Department of Functional Anatomy, ACTA, Amsterdam, The Netherlands; *corresponding author, etanaka@ dent.tokushima-u.ac.jp J Dent Res 87(11):989-991, 2008
Biomechanics of the Temporomandibular Joint
his article is in honor of the late professor Theo van Eijden, who passed away on February 28, 2007. During his career as chairman of the Department of Functional Anatomy at the Academic Centre for Dentistry Amsterdam, he was very productive in his contributions to our understanding of the biomechanics of the human masticatory system. First and foremost, however, he was a great inspiration for his fellow researchers, from both his own institute and beyond. Temporomandibular joint (TMJ) disorders were recognized in the early dental (Gysi, 1921) and medical (Costen, 1997 [reprinted from 1934]) literature as an individual source of facial pain. The function of this joint, however, was not regarded as important. For instance, initially, the TMJ was not considered to be a load-bearing joint. Also, the movement possibilities of the joint were poorly understood, as illustrated by a persistent belief in the concept of a more or less ‘predetermined’ instantaneous center of rotation (Grant, 1973). One of the major complicating factors in comprehension of the function of the TMJ is the presence of its disc, which, in certain circumstances, appears to be able to dislocate temporarily or permanently. In the latter case, this can lead to degeneration and may cause severe pain and/or masticatory dysfunction. The causes for such a disc displacement as well as its consequences are not yet understood. Treatment remedies for TMJ dysfunction include medication (for example, NSAIDs), conservative approaches (for example, splint therapy), and physical therapy. In addition, in end-stage disease, such as TMJ osteoarthrosis, surgery may be considered. This may range from disc removal to complete joint replacement. The decision for treatment modalities must be based on evaluation of the individual’s response to non-invasive management, his/her mandibular form and function, and the impact of the modality on the individual’s quality of life (Mercuri, 2006). Unfortunately, predictions about the latter must be based primarily on prior experience. Obtaining causal relationships is very difficult, because the joint cannot be reached easily, and there are few experimental methods that have been proven to be adequate for: (1) decreasing joint pain, (2) increasing
joint function, (3) preventing further joint damage, and (4) preventing disability and disease-related morbidity (Tanaka et al., 2008). If such information were available, it would enable dentists to manage patients with TMJ disorders correctly at earlier stages, such that the necessity for surgical treatment would decrease. In the field of orthopedics, a three-dimensional reconstruction system has already been developed as a powerful tool for diagnosis and treatment planning of bone fracture (Glitsch and Baumann, 1997; McLean et al., 2003). The latter, for instance, successfully developed a subject-specific threedimensional model of the lower extremity from an individual MRI and used it to predict neuromuscular control effects on three-dimensional knee joint loading during movements that can potentially cause injury to the anterior cruciate ligament in the knee. These investigators also demonstrated that this modeling was successful in simulating injuries caused by perturbed neuromuscular control, which can contribute to the prevention of damage to the locomotory system. The goal of TMJ research should be the development of a system to diagnose TMJ disorders and their etiology. This would include three-dimensional reconstruction...