In which areas should alginate material be pre-injected before seating the tray for a master impression?

The correct choice highlights the importance of ensuring that alginate material is adequately applied to both rest seats and vestibules before seating the tray for a master impression.

Pre-injecting alginate into the rest seats is crucial because these areas are designed to support the partial denture and must accurately capture their contours to ensure a proper fit and function of the prosthesis. By filling these areas, the impression will more precisely reflect the relationship between the remaining teeth and the soft tissue, contributing significantly to the retention and stability of the future denture.

The vestibules, or the spaces between the lips and cheeks and the gums, are also key areas where alginate should be injected. These regions help define the borders of the denture and ensure that the impression captures the dynamic movements of the cheeks and lips, which influence the design of the partial denture.

Having sufficient material in these areas allows for optimal capture of details, ensuring that the final impression leads to a fully functional and aesthetically pleasing removable partial denture. Proper coverage in both locations helps prevent impression distortion and ensures that all necessary anatomical features are recorded accurately.