When a fixed prosthesis is to be constructed, which impression material will not be used?

In the context of constructing a fixed prosthesis, alginate is typically not the preferred impression material due to its characteristics. Alginate is a hydrocolloid impression material that is mainly used for making initial impressions or study models, primarily because it is easy to use and relatively inexpensive. However, its dimensional stability is less reliable compared to other materials, and it can be affected by moisture and time, which may compromise the accuracy needed for definitive restorations like fixed prostheses.

In contrast, addition silicone, polyether, and polyvinyl siloxane are all elastomeric materials that offer superior detail reproduction and dimensional stability, making them suitable choices for the high-precision requirements of fixed prosthodontics. These materials are better suited for capturing detailed impressions of the prepared tooth and surrounding structures, ensuring a more accurate fit for the final prosthesis. Thus, while alginate may be useful in some dental procedures, it is not appropriate for creating impressions for fixed prostheses where accuracy is paramount.