Current status of temporomandibular joint disorders and the therapeutic system derived from a series of biomechanical, histological, and biochemical studies

Abstract

This article was designed to report the current status of temporomandibular joint disorders (TMDs) and the therapeutic system on the basis of a series of clinical, biomechanical, histological and biochemical studies in our research groups. In particular, we have focused on the association of degenerative changes of articular cartilage in the mandibular condyle and the resultant progressive condylar resorption with mechanical stimuli acting on the condyle during the stomatognathic function. In a clinical aspect, the nature and prevalence of TMDs, association of malocclusion with TMDs, association of condylar position with TMDs, association of craniofacial morphology with TMDs, and influences of TMDs, TMJ-osteoarthritis (TMJ-OA) in particular, were examined. In a biomechanical aspect, the nature of stress distribution in the TMJ from maximum clenching was analyzed with finite element method. In addition, the pattern of stress distribution was examined in association with varying vertical discrepancies of the craniofacial skeleton and friction between the articular disk and condyle. The results demonstrated an induction of large compressive stresses in the anterior and lateral areas on the condyle by the maximum clenching and the subsequent prominent increases in the same areas of the mandibular condyle as the vertical skeletal discrepancy became more prominent. Increase of friction at the articular surface was also indicated as a cause of larger stresses and the relevant disk displacement, which further induced an increase in stresses in the tissues posterior to the disks, indicating an important role of TMJ disks as a stress absorber. In a histological or biological aspect, increase in TMJ loading simulated by vertical skeletal discrepancy, which has already been revealed by the preceding finite element analysis or represented by excessive mouth opening, produced a decrease in the thickness of cartilage layers, an increase in the numbers of chondroblasts and osteoclasts and the subsequent degenerative changes in the condylar cartilage associated with the expression of bone resorption-related factors. In a biochemical or molecular and cellular aspect, excessive mechanical stimuli, irrespective of compressive or tensile stress, induced HA fragmentation, expression of proinflammatory cytokines, an imbalance between matrix metalloproteinases and the tissue inhibitors, all of which are assumed to induce lower resistance to external stimuli and degenerative changes leading to bone and cartilage resorption. Excessive mechanical stimuli also reduced the synthesis of superficial zone protein in chondrocytes, which exerts an important role in the protection of cartilage and bone layers from the degenerative changes. It is also revealed that various cytoskeletal changes induced by mechanical stimuli are transmitted through a stretch-activated or Ca2+ channel. Finally, on the basis of the results from a series of studies, it is demonstrated that optimal intra-articular environment can be achieved by splint therapy, if indicated, followed by occlusal reconstruction with orthodontic approach in patients with myalgia of the masticatory muscles, and TMJ internal derangement or anterior disk displacement with or without reduction. It is thus shown that orthodontic treatment is available for the treatment of TMDs and the long-term stability after treatment.

Mechanical Stress Induce PG-E2 in Murine Synovial Fibroblasts Originating from the Temporomandibular Joint

“…In healthy TMJ joints, the disc acts as a stress absorber, while enabling cooperative movement with condylar repositioning during jaw movement. When exceeding stress affects the joint, disc displacement may occur with transmission to the surrounding tissues [ 46 ]. As the TMJ is—apart from the knee and clavicular joints—the only synovial joint with an articular disc, research in this topic reveals important insights in understanding osteoarthritis [ 46 ].…”

“…When exceeding stress affects the joint, disc displacement may occur with transmission to the surrounding tissues [ 46 ]. As the TMJ is—apart from the knee and clavicular joints—the only synovial joint with an articular disc, research in this topic reveals important insights in understanding osteoarthritis [ 46 ]. TMJ OA is an important disease in orthodontics and a fundamental factor in the reduction of quality of life.…”

Comparative assessment of condylar position in patients with temporomandibular disorder (TMD) and asymptomatic patients using cone-beam computed tomography

“…[30][31][32] The condylar position was more posterior in anterior disk displacement with reduction, and more concentric and anterior in anterior disk displacement without reduction. 33 Yang et al selected a total of 52 TMJs with the anterior, concentric and posterior condylar position. 14 They traced the condylar movements by simulating mandibular movements with 3D CT data and a position tracking camera.…”

Cone-beam computed tomographic evaluation of the temporomandibular joint and dental characteristics of patients with Class II subdivision malocclusion and asymmetry

“…Our results regarding the relationship between mandibular first molar position and the condyle-glenoid fossa suggested that the condylar height was smaller when the mandibular first molar showed greater distal movement, and the glenoid fossa simultaneously moved deeper. Tanne et al 26 showed that the great compressive stresses produced in the anterior and lateral regions of the mandibular condyle subsequently increased with the vertical skeletal discrepancy. The decrease in condylar height and increase in glenoid fossa depth might be due to the stresses between the condyle and glenoid fossa exerted during the process of mandibular molar distal movement.…”