Ontogenesis of the Human Temporomandibular Joint

1. Development of the Condyles

¹ Institut de Medecine Dentaire, Universite de Geneve, Geneva, Switzerland

Embryogenesis of the mandibular condyles was assessed in a material of 12 human fetuses of ascending stages from 15 to 72-mm. crown-rump length. It was found that condylar cartilage formation was a phenomenon closely related to the morphogenesis of the entire mandible and skull. Secondary cartilage appeared simultaneously at all sites of the insertion of the masticatory muscles. At the same time, the anterior portion of Meckel's cartilage was incorporated into the mandibular body by a process of endochondral ossification. The condyle originated from a mesodermal condensation which was situated at the dorsal end of the dentary, in the vicinity of the proximal end of the lateral pterygoid muscle. This so-called condylar blastema appeared at the 24-mm. CR stage; at the early stages it contributed to the growth of the muscle and the dorsal prolongation of the dentary. At the 55-mm. CR stage, rapid osteogenesis led to the formation of a condylar head with no cartilage present. At the tenth week of fetal life (60 mm. CR), as the culmination of this growth spurt, chondrogenesis started at the dorsolateral portion of the blastema; concomitantly, the tendinous attachment of the lateral pterygoid muscle was differentiated, while, at the condylar neck, periosteal bone formation was proceeding. Endochondral ossification was not primarily involved in the formation of the condyles; it was still absent at the 72-mm. CR stage. Neither was there, up to this stage, any obvious developmental relations between condyle and temporal joint elements.

The late maturation of the condylar blastema was shown to coincide chronologically with the growth spurt of the prechordal segment of the cranial base.

Ontogenetically, the mandible is a "mixed bone"; it originated as a pure membrane bone, then incorporated elements of the Meckel's cartilage primordium, and finally developed at various sites secondary cartilage. Of these, only the condylar cartilage persisted to form ultimately the highly organized growth center of the mandible.