a. Bones. The temporomandibular joint derives its name from the two bones
that form the joint, the temporal bone and the mandible. The condyloid process of the
mandible and the mandibular fossa of the temporal bone form the joint. The condyle
moves (articulates) inside the fossa and makes the movements of the mandible
possible. It provides for up and down movements (elevation and depression), forward
and backward movements (protrusive and retrusive), and side-to-side movements
(lateral and rotational).
b. Articular Disc. The articular disc is a thin, biconcave, oval plate made of
fibrous tissue, located between the mandibular fossa and the condyle of the mandible
and the articular tubercle (posterior tubercle) of the temporal bone. The disc divides the
TMJ into upper and lower cavities, each having synovial membranes which secrete
synovial fluid to lubricate the joint. The edges of the disc are attached to the capsular
ligament and, in front, it is attached to the lateral pterygoid muscle.
c. Ligaments. A ligament is a tough, fibrous band that connects bones. There
are four ligaments that limit the extreme movement of the mandible. These are the
capsular ligament, the lateral (temporomandibular) ligament, the sphenomandibular
ligament, and the stylomandibular ligament.
d. Movements of the Mandible. The articulating joint of the mandible allows
for a combination of movements, such as hinge, lateral, and protrusive movements.
Different types of teeth perform various functions (incisors and cuspids for cutting,
bicuspids and molars for crushing) The articular disc is situated between the condyle
and the fossa to allow for the many different movements and functions required by
different teeth. To contain the TMJ and to seal in the synovial fluid, the TMJ is
encapsulated by the capsular ligament with a synovial lining. Thus, the TMJ is
protected from wear and can absorb minor blows to the jaw.
e. Use of Articulators. Articulators, metal instruments used in the making of
dentures, are designed to reproduce the movements of the mandible. The
temporomandibular joint and jaw movements vary widely from person to person.
Nonadjustable articulators are designed to reproduce the average articulation
measurement for most individuals. The vast majority of prosthetic restorations can be
accomplished using average jaw movements. For those situations where more precise
reproduction of jaw movements is required, adjustable articulators are available.