Which of the following could indicate the need for a functional reline based on border extensions?

The need for a functional reline based on border extensions is primarily indicated by a lack of appropriate border extensions. In removable partial dentures, the borders play a crucial role in ensuring stability, retention, and proper function of the prosthesis.

When the borders of the denture are inadequate — meaning they do not extend sufficiently to adequately engage the underlying tissues or accommodate the functional movements during activities such as chewing or speaking — it can lead to issues such as dislodgment or discomfort for the patient. Proper border extensions allow for the functional movement and dynamic adaptation of the denture, ensuring that it stays in place during use.

Other options, such as having a thick denture base, an unstable arch form, or overriding occlusal contacts, do not specifically relate to the effectiveness of border extensions in the same direct way. While they can affect the overall fit and function of the denture, they do not specifically indicate the need for a functional reline due to insufficient border engagement. Therefore, the correct choice highlights the importance of adequate border extensions for the effective performance of a removable partial denture.