Final answer:
The most common primary tooth to become ankylosed is a mandibular molar due to the fusion of the tooth to the jawbone, often affecting the primary molars in the lower jaw (mandible).
Step-by-step explanation:
The most common primary tooth to become ankylosed is a mandibular molar. Ankylosis of teeth is a condition where a tooth becomes fused directly to the bone, preventing the tooth from erupting or moving normally. This can lead to various dental issues, including disrupting the eruption of permanent teeth. While ankylosis can occur with any tooth, it more frequently affects the primary mandibular molars compared to maxillary molars or canines. These teeth are held in their sockets by the periodontal ligament, and when ankylosis occurs, this ligament becomes compromised or even absent, thus fusing the tooth to the jawbone – typically seen in the mandible.