Which material is commonly used to evaluate the fit of an RPD base at the placement appointment?

The evaluation of the fit of a removable partial denture (RPD) base at the placement appointment typically involves the use of PIP paste. This material is specifically designed for this purpose, as it is a thin, viscous paste that provides a clear indication of contact points between the denture base and the underlying soft tissue when pressure is applied.

When PIP paste is used, any areas where the paste is displaced indicate a discrepancy in fit that requires adjustment. The coloration and thickness of the paste help the clinician identify high spots or areas where the denture is not seating properly, allowing for precise modifications to enhance comfort and function.

In contrast, the other materials listed have different intended uses. Silicone impression materials are primarily used for creating accurate impressions for prosthetic applications rather than for assessing fit on the spot. Alginate is typically used for making preliminary impressions, not for fit evaluation, as it can distort easily. Automix polyether is used for detailed impressions and also focuses on capturing the precise shape of teeth and their surrounding tissues rather than checking the fit of an existing RPD. Thus, PIP paste stands out as the best option for evaluating RPD fit at the placement appointment.