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The norm of the temporomandibular joint on the x-ray
Last reviewed: 19.10.2021
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Temporomandibular joint - articulation formed by the head of the condylar process and the articular surface of the mandibular fossa of the temporal bone, is fully formed by 15-17 years. The articulating surfaces are separated by a cartilaginous articular disc on the upper and lower divisions. On the periphery of the head, constructed from trabecular spongy bone substance, the closing cortical plate passes. Its thickness in the anterior and posterior regions is 0.75-1.5 mm, over the upper surface 0.5-1 mm.
The compact layer covering the mandibular fossa is variable in different departments. In the posterior regions, a broad band of compact matter merges with the shadow of the pyramid of the temporal bone. The most thin is a compact layer in the central part of the articular cavity, anteriorly it passes into the cortical layer of the posterior stump of the tubercle. In the middle of the posterior part of the mandibular fossa, a stony-tympanic (glazer) fissure is visible, which extends toward the lumen of the external auditory canal. This gap serves as a guide between the extra- and intra-articular portions of the fossa.
The external auditory meatus is defined as a clearly contoured enlightenment of an irregularly rounded form 0.8-2 cm in diameter against the background of an intense shadow of the stony part of the temporal bone pyramid.
On the lateral tomogram in the state of physiological rest, the width of the X-ray joint gap in all sections is equal or somewhat wider between the anterior arch of the head and the posterior slope of the joint artery.
When the mouth is opened, the head moves downwards and forward along the posterior slope of the articular tubercle, reaches the apex of the tubercle or even enters the front ramp (in children).
For the purpose of analyzing tomograms and measuring different parts of the joint, they are repainted on tracing paper. To do this, draw a line connecting the lower edges of the articular tubercle and the external auditory canal, and perpendicular from the upper point of the articular fossa is lowered onto it. At an angle of 45 ° to the horizontal line at the intersection with the perpendicular, two more lines are drawn. The width of the articular gap between the articular tubercle and the front surface of the articular head is designated as the anterior section of the gap, between the bottom of the articular fossa and the upper surface of the joint head - as the upper part of the gap, between the posterior surface of the head and the posterior part of the articular cavity - as the posterior part of the joint space.
Involutive changes lead to aging of the cartilage, disruption of the function of the joint, the appearance of bone growth, against the background of osteoporosis, the cortical plates are clearly contoured.