Which of the following is NOT a clinical sign of mobility in teeth?

The widened periodontal ligament (PDL) space is indeed a clinical sign of mobility in teeth. It indicates that there is a breakdown of the supporting structures around the tooth, often due to periodontal disease or trauma. As the periodontal ligament becomes compromised, the space between the tooth root and the surrounding bone increases, which is an observable characteristic in cases of tooth mobility.

Tooth mobility itself, which can be directly observed during a clinical examination, clearly indicates that the tooth is not securely anchored in the alveolar bone. Displacement during percussion is another aspect that reflects tooth mobility, as it demonstrates that the tooth can move within its socket when force is applied.

Gum recession, while it can be a related symptom or consequence of periodontal disease, does not directly indicate tooth mobility on its own. It is more of an indicator of periodontal health rather than a direct sign of the mobility of the tooth itself. Therefore, it is appropriate to conclude that the widened PDL space, tooth mobility observed, and tooth displacement during percussion are all clinical signs of tooth mobility, while gum recession does not serve this function in the context of assessing tooth mobility.