Prof. Doutor

RESEARCH REPORTS
Biological

Q. Huang1, D. Opstelten2, N. Samman1*, and H. Tideman1
1Department

of Oral & Maxillofacial Surgery, Faculty of Dentistry, Prince Philip Dental Hospital, 34 Hospital Road, and 2Department of Biochemistry, Faculty of Medicine, The University of Hong Kong, Hong Kong; *corresponding author, nsamman@hkucc.hku.hk J Dent Res 81(3):209-213, 2002

ExperimentallyInduced Unilateral Tooth Loss: Histochemical Studies of the Temporomandibular Joint

ABSTRACT
Occlusal abnormality may contribute to osteoarthrosis of the temporomandibular joint (TMJ). Since mechanical force may induce changes in the extracellular matrix, we tested the hypothesis that unilateral removal of teeth and the resulting unilateral mastication change the content of glycosaminoglycans(GAGs) in the TMJ condyle and disc. Lower-right-side teeth were extracted from 12 adult male rabbits, which were killed 3 or 6 weeks later. Three normal rabbits served as controls. Sections were analyzed for morphological changes and levels of sulfated GAGs in the condyle and disc. Unilateral removal of teeth led to thickening of the condylar cartilage, alterations in the morphology of chondrocytenuclei in the condylar cartilage and disc, and increases in levels of negatively charged ions in the hypertrophic layer of condylar cartilage. Small differences were observed, after unilateral removal of teeth, between the functional and nonfunctional sides of the TMJ. The results suggest that in response to mechanical stress, chondrocytes alter sulfated glycosaminoglycan (GAGs) synthesis anddegradation rates, resulting in an elevated level of sulfated GAGs in the condylar cartilage.

INTRODUCTION
osteoarthrosis is thought from an Temporomandibular joint (TMJ)altered joint morphology to resultstructural imbalance between predominantly chondrocyte-controlled anabolic and catabolic processes and leads to due to changes of the tissues concerned and joint remodeling (de Bont, 1996). Althoughthe etiology of TMJ osteoarthrosis is still not fully elucidated and is certainly multifactorial (Dijkgraaf et al., 1995; Haskin et al., 1995), occlusal abnormalities are considered as one possible factor contributing to TMJ osteoarthrosis (Kamelchuk and Major, 1995). Biomechanical factors such as occlusal and masticatory dysfunction, loss of posterior teeth, unilateral chewing patterns, andbruxism have been proposed to be involved in the initiation and progression of degenerative TMJ disease through absolute or relative overloading of joint structures (Haskin et al., 1995). Histological studies have shown that unilateral tooth extraction leads to changes in the TMJ. Studies in humans and rats show disturbance of the local microcirculation, wavy irregular fibers in the disc, smaller andcondensed chondrocytes in the condylar cartilage, and destruction of articular cartilage of the TMJ (Granados, 1979; Christensen and Ziebert, 1986; Fujita and Hoshino, 1989; Ma and Pi, 1993; Hu et al, 1996). Thickening of the TMJ articular cartilage in rats after unilateral and bilateral removal of teeth (Furstman, 1965), and in Macaca mulatta with occlusal splints (Gianelly et al., 1970), has alsobeen observed by light microscopy. TMJ cartilage is mainly composed of water, collagen, and proteoglycans. Over 90% of the weight of the proteoglycan molecule in the extracellular matrix of normal TMJ cartilage is made up of negatively charged glycosaminoglycans (GAGs), mostly sulfated GAGs (Muir, 1983; Dijkgraaf et al., 1995). Sulfated GAGs, found in tissues normally exposed to load, may bind tocationic dyes such as safranin O. Safranin O staining is increased in the condylar cartilage of rabbits with unilateral bite raise (Mao et al., 1998). With increased mechanical force on the rat TMJ, synthesis of GAGs is increased, as shown by autoradiography (Corpray et al., 1985). Analysis of these data indicates that TMJ chondrocytes respond to changes in mechanical force, leading to an...