By around 12 weeks in TMJ development, which structure forms?

• A. Articular disc
• B. Tooth enamel
• C. Glenoid fossa remodeling
• D. Condylar cartilage

Answer: (A)

In TMJ development, the key event is the formation of intra-articular structures within the developing joint capsule. By about 12 weeks, a distinct articular disc has formed between the condyle and the temporal bone, inside the capsule. This fibrous disc splits the joint into superior and inferior compartments, enabling both sliding and rotating movements of the mandible as development progresses. The other options don’t fit this timing or location: tooth enamel forms from tooth germs in the jaws, not within the TMJ itself; remodeling of the glenoid fossa occurs later as the temporal bone matures; and the condylar cartilage appears early as a growth center in the condyle but is not the discrete intra-articular disk that forms by this stage.