Which dental instrument is designed to adapt filling materials to the shape of cavities?

The flat plastic is specifically designed to adapt filling materials to the contours of cavities. This instrument features a flat, smooth working end that allows the dental nurse or dentist to shape and smooth filling materials, such as composite resins or glass ionomers, into the cavity's anatomy. The smooth surface helps to ensure a better adaptation of the material to the tooth structure, which is crucial for a well-sealed restoration that minimizes the risk of secondary decay and enhances the longevity of the filling.

In contrast, other instruments listed serve different primary functions. An amalgam plugger is primarily used to condense amalgam into the cavity preparation but does not shape the material in the same way the flat plastic does. A Ward’s caver is generally used for carving and contouring materials but does not specifically adapt materials as effectively for the early shaping of filling materials. The diamond bur is a rotary instrument used for cutting or shaping teeth and other dental materials but is not designed for the adaptation of filling materials. Therefore, the flat plastic emerges as the most appropriate choice for achieving the desired contouring of filling materials within cavities.