The Morphogenesis of the Human Temporomandibular Joint and Its Associated Structures

¹ School of Dentistry, University of Washington, Seattle, Washington

Several conflicting theories proposed by previous investigators regarding the prenatal development of the temporomandibular joint indicated the need for further study of the subject. The prenatal development of the temporomandibular joint and its related structures were studied in a total of 25 human embryos and fetuses, 13 to 370 mm. in crown-rump length, or approximately six weeks to full term. These were prepared for serial sectioning.

Ossification of the mandibular element of this joint first appeared during the sixth-week stage; whereas, in the temporal element, it appeared during the eighth-week stage. The temporal element, however, soon reached the mandibular development rate and, by the 12th-week stage, the joint elements had initially situated at some distance from each other and were developing in opposite directions, finally reaching their closest approximation.

The greatest changes in the joint region occurred between the tenth and 12th week. This coincided with the close approximation of the two skeletal elements. Preskeletal tissue appeared in several regions to form secondary cartilaginous growth centers. Condylar cartilage, appearing at the tenth-week stage, accounted for a gross morphologic change in the mandible. The peculiar ossification pattern of the condylar cartilage seemed to determine the direction of growth of the condylar cartilage. Both joint cavities, also appearing during this interval, subsequently defined the articular disk.

Highly vascular mesenchyme was found to be closely related to the formation of the capsule, anterior rim of the articular disk, and retrodiscal pad. The thin central portion of the articular disk, being quite distinct long before skeletal approximation and joint cavitation, was thought to be a derivative of the condylar blastema. This ruled out the possibility of a direct formation by compression of intra-articular tissue.

The role of the external pterygoid muscle in the joint's formation was complex. At the seventh-week stage, it outlined a region that was destined to be the future dorsal end of the mandible. Both the external and internal pterygoid muscles demonstrated a partial attachment to Meckel's cartilage. Beyond this stage, the external pterygoid muscle was not seen to attach to Meckel's cartilage, but its fibers, now lying horizontally, followed the dorsally developing condylar process to its final position. There was no evidence at any stage that this muscle either was attached to the malleus or contributed to the articular disk.

This article has been cited by other articles:

				J.F. Rodriguez Vazquez J.R., M. Velasco, and J. Jimenez Collado Relationships between the Temporomandibular Joint and the Middle Ear in Human Fetuses Journal of Dental Research, January 1, 1993; 72(1): 62 - 66. [PDF]

				R. D. Coleman Temporomandibular Joint: Relation of the Retrodiskal Zone to Meckel's Cartilage and Lateral Pterygoid Muscle Journal of Dental Research, May 1, 1970; 49(3): 626 - 630. [PDF]

				C.H. Tonge The Time-Structure Relationship of Tooth Development in Human Embryogenesis Journal of Dental Research, September 1, 1969; 48(5): 745 - 752. [Abstract] [PDF]

				R. A. Yuodelis Ossification of the Human Temporomandibular Joint Journal of Dental Research, January 1, 1966; 45(1): 192 - 198. [PDF]