Which of the following indicates a need for further investigation in a root canal treated tooth?

The presence of radiolucency is a significant indicator that further investigation is needed in a root canal treated tooth. Radiolucency refers to areas on an x-ray that appear darker than the surrounding structures, indicating potential pathological changes such as infection, inflammation, or failure of the root canal treatment. This sign suggests that there may be underlying issues in the periapical region, which could require additional diagnostic measures such as more advanced imaging, retreatment of the root canal, or possibly surgical intervention.

Other factors, such as the absence of pain, presence of pain with normal x-ray findings, or no change in mobility, do not necessarily indicate an immediate need for further investigation. For instance, the absence of pain could signify that the tooth is healthy, while the presence of pain with a normal x-ray may require monitoring rather than immediate action, as pain can occasionally arise from other sources. Similarly, no change in mobility indicates stability, which does not inherently signal further complications. Thus, radiolucency stands out as a clear marker that necessitates further scrutiny.