The Anatomy of Joints Related to Function
Verna Wright, Eric L. Radin in Mechanics of Human Joints, 2020
The menisci of the knee are perforated rings, but in other situations intraarticular disks may separate the joint cavity completely into two compartments. In these circumstances, different movements are facilitated on opposite sides of the disk. This is the case in the temporomandibular joint (Fig. 3B), where the intraarticular disk is complete and is attached to the circumference of the joint capsule. It conforms to the mandibular fossa on the temporal bone and can slide forward out of this depression, carrying the mandibular condyle with it. The disk has a direct connection to the posterior margin of the fossa, but this does not prohibit its anterior displacement because this attachment is significantly composed of elastic fibers; elsewhere, the capsule between disk and temporal bone is lax (52). Beneath the disk, movement between it and the mandibular condyle is constrained to rotation about a transverse axis by stout attachments directly to medial and lateral poles of the condyle. These attachments are analogous to the collateral ligaments of a hinge-type joint; anteriorly and posteriorly the “subdiskal” capsule is lax and permits the necessary movement (52).
Musculoskeletal system
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha in Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
The temporomandibular joint (TMJ) is a synovial condyloid joint formed between the head (condyle) of the mandible and the mandibular fossa of the temporal bone (Fig. 3.50). The anterior part of the mandibular fossa, with which the head of the mandible articulates when the mouth is opened, is termed the articular tubercle. The joint capsule is attached superiorly to the rim of the articular surface and inferiorly to the neck of the mandible. The capsule is strengthened laterally to form the lateral or temporomandibular ligament. Intrinsically there is an interarticular disc (meniscus) that divides the joint into the superior and inferior cavities. It is attached to the periphery of the capsule and is situated over the head of the mandible, projecting anteriorly towards the tubercle. A number of small muscles combine to produce depression, elevation, protrusion, retraction and lateral movements of the mandible. These movements are complex, and the action of opening the mouth results in the head of the mandible moving downwards and forwards. Excessive movement can result in anterior dislocation of the head of the mandible on the articular tubercle. The joint derives its blood supply from the temporal and maxillary branches of the external carotid artery.
Effects of introducing gap constraints in the masticatory system: A finite element study
J. Belinha, R.M. Natal Jorge, J.C. Reis Campos, Mário A.P. Vaz, João Manuel, R.S. Tavares in Biodental Engineering V, 2019
The temporomandibular joint (TMJ) is a synovial joint which articulates the jaw to the skull. It is composed principally by the mandibular condyle, the mandibular fossa, the articular disc, the capsule, the ligaments and the lateral pterygoid muscle. The articulating surfaces of the condyles and the mandibular fossa are covered with articular cartilage, which together with the synovial fluid allows for a very low coefficient of friction and a uniform transmission of compressive forces to the bone (Radin et al. 1971). The articular cartilage of the TMJ contains both collagen fibers type I and type II, which classifies it as fibrocartilage. Due to the low permeability of the tissue, compression forces rapidly increase fluid pressure, which in turn carries the major part of the load through hydrostatic pressurization (Mow et al. 2005). The collagen fibers of the cartilage, on the other hand, resist the stretching of the tissue from tensile forces (Hukins et al. 1984). The articular disc, also composed of fibrocartilage, lies between the mandibular condyle and the fossa, dividing the synovial joint in two. It distributes loads and dissipates the energy caused from impact loads. The disc allows for relative motion between the condyle and the temporal bone. In the case of the condyle, both translational and rotational motions are possible. The articular disc is connected to the articular surfaces through the joint capsule. The attachments of the joint capsule can be divided as shown in Figures 1–2 into medial, lateral, anterior and posterior attachments. These attachments give the disc a range of movement and at the same time avoid extreme displacements that may result in the dislocation of the disc.
Occlusal load modelling significantly impacts the predicted tooth stress response during biting: a simulation study
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Harnoor Saini, David C. Ackland, Lulu Gong, Oliver Röhrle
To this end, dental structures, including the first right mandibular molar enamel and dentin, the cortical and cancellous mandibular bone, and a section of the left and right mandibular fossa, were manually segmented from the CT scans using ITK-SNAP (version 2.4.0) (Yushkevich et al. 2006). Since dentin and cementum have similar mechanical properties (Shaw et al. 2004), these materials were combined into one structure. The thickness of the articular discs of the TMJ was defined from the width of the space between the mandibular condyles and the fossae. The periodontal ligament (PDL) geometry was based on the mandibular molar root geometry and defined as a uniform layer with an approximate thickness of 0.20 mm similar to other investigations (e.g. McGuinness et al. 1992; Toms and Eberhardt 2003). The maxillary first molar geometry was segmented from the micro-CT images. The rubber sample used in the biting simulations had dimensions 20x10x5mm (Röhrle et al. 2018).
Analysis of temporomandibular joint dysfunction in paediatric patients with unilateral crossbite using automatically generated finite element models
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Javier Ortún-Terrazas, José Cegoñino, Edson Illipronti-Filho, Amaya Pérez del Palomar
The temporomandibular joint (TMJ) is a complex mandibular articulator composed primarily of the TMJ disc, hyaline cartilages, and the disc attachments. The TMJ mainly develops during paediatric growth in response to the mechanical stimuli produced during chewing by the elevator (masseter, temporalis, medial pterygoid, and superior portion of the lateral pterygoid) and depressor (digastric, geniohyoid, mylohyoid, and the inferior portion of the lateral pterygoid) muscles (Bakke 2006; Chan et al. 2008). Healthy bilateral chewing occurs in an alternating manner: while one condyle compresses the TMJ disc with the mandibular fossa (working movement), the other moves the articular eminence forward (balancing movement) (Palla et al. 2003). While well-balanced chewing ensures proper development of both TMJs, unilateral crossbite (UXB) may result in morphological deformities in the TMJs.
Temporomandibular joint stability after two types of maxillary impaction surgery in patients with skeletal class II open bite due to condylar deformations: a preliminary study
Published in Orthodontic Waves, 2021
Koichi Fujita, Shuhei Minamiyama, Risa Usumi-Fujita, Susumu Omura, Hikaru Takasu, Yosuke Yamashita, Koji Honda, Haruki Imai, Toshinori Iwai, Makoto Hirota, Takashi Ono, Kenji Mitsudo
Recently, the occurrence of post-surgical condylar resorption or progressive condylar resorption (PCR) has received clinical attention as orthognathic surgery has gained popularity. The occurrence of PCR in association with mandibular osteotomies that aim at anterior mandibular advancement to increase the size of the small lower jaw is particularly high, with a global incidence of 6–20% [15]. PCR is defined as a progressive morphological change in the mandibular condyle and is accompanied by a significant reduction in the height of the ramus, resulting in symptoms such as maxillary protrusion, open bite, and facial asymmetry [16]. On the other hand, OA is a degenerative joint disorder characterized by the destruction of the mandibular joint tissue with cartilage and bone changes in the condylar head and mandibular fossa/articular ridge. In this study, we confirmed the condylar deformity using pre-surgical CT and used the term OA simply because we did not ascertain the presence or absence of progression over time.
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