When seating an impression tray, which part should be seated first?

When seating an impression tray, the correct approach is to seat the posterior teeth first. This technique ensures a more accurate impression by helping the tray to comfortably fit into the mouth and allowing for proper alignment with the natural contours of the dental arch. By starting posteriorly, the operator can easily push the tray into place without causing discomfort to the patient, as the back of the tray can serve as a guide for the rest of it moving forward.

Additionally, seating the posterior aspect first helps to minimize air pockets and ensures that the impression material flows correctly into the space around all teeth. It also allows the operator to determine the tray's correct positioning more effectively before securing the anterior part of the tray. Therefore, starting with the posterior teeth is a critical step in achieving a precise and well-defined impression.