Which of the following conditions would indicate bonded retainer failure?

Tooth mobility is a key indicator of bonded retainer failure because it often suggests that the retainer is no longer providing the necessary support to maintain proper tooth alignment. A bonded retainer serves to stabilize the teeth after orthodontic treatment, preventing movement. If the teeth exhibiting mobility are supported by the retainer, this suggests that the bonding of the retainer may have become compromised, allowing the teeth to move more freely than intended.

While visible decay, change in tooth color, and gingival hyperplasia can all impact the health of the teeth and surrounding tissues, these conditions do not specifically indicate that the retainer itself has failed. Visible decay might point to underlying issues but doesn’t directly reflect the mechanical integrity of the retainer. A change in tooth color could be caused by numerous factors, including diet or dental hygiene, rather than the state of the retainer. Gingival hyperplasia may arise from various causes, such as medication use or systemic conditions, and is not an exclusive sign of retainer failure. Hence, tooth mobility directly relates to the function of the bonded retainer, making it the most relevant indicator of failure.