Development of the human temporomandibular joint. Computer-aided 3D-reconstructions

Computer-aided graphical three-dimensional reconstructions of histological serial sections of 12 human embryos and fetuses (25-250 mm Crown-rump lengt h (CRL)) were used to trace the prenatal development of the elements of the human temporomandibular joint. The primordia of the condylar and coronoid processes could be identified as two bony peaks at the dorsal ends of the m andible at the stage of 25 mm CRL. The primordium of the temporal bone alre ady existed at the stage of 37 mm CRL. The bone was apparent with a convex contour towards the condyle. The glenoid fossa was not yet visible. At 65 m m CRL, the osseous glenoid fossa could be distinguished at the enlarged tem poral bone formation. The glenoid fossa developed posteriorly and medially from the condyle and extended in cranial and anterior direction. The glenoi d fossa had various contours, changing from flat and slightly convex (65 mm CRL) to concave (250 mm CRL) with an articular tubercle. The distance betw een fossa and condyle increased proportionally. The lower joint cavity appe ared at an earlier stage (65 mm CRL) than the upper joint cavity (70 mm CRL ). Both cavities started development as isolated compartments fusing later on. The upper joint cavity followed the contour of the fossa, whereas the l ower joint cavity followed the form of the condyle. The biconcave shape of the articular disc as well as the attachment of the lateral pterygoid muscl e could be observed very early (70 mm CRL).