To allow muscle attachments, the border of the tray should be?

The correct answer is that the border of the tray should extend about 3 to 5 mm cervical to the gingival margins. This extension is crucial for several reasons. Firstly, it ensures that there is an adequate space for the muscles of mastication and other functional movements without interference from the tray. By positioning the tray slightly below the gingival margin, it allows the impression material to capture the soft tissue anatomy accurately while avoiding distortion due to muscle movements.

This design consideration reinforces the need for a proper impression to ensure that the prosthetic device fits well and functions correctly in the oral cavity. Furthermore, extending the tray to this position helps in achieving a more precise detail of the impression, which is vital for the overall success of prosthetic rehabilitation.

In contrast, placing the tray farther than the demarcation between the soft and hard palate would not provide the necessary support for the impression material while potentially missing important anatomical details. Rigidly attaching the tray to muscle attachments would restrict the necessary movements and lead to inaccuracies, while aligning the tray exactly at the gingival margin may also inhibit the capture of vital soft tissue information needed for fitting the final prosthetic. Thus, extending the tray 3 to 5 mm below the gingival margin is the most