Which instruments are typically used to place amalgams or composite resins into preps?

The correct choice is compactors, as they are specifically designed to condense and shape dental materials like amalgams and composite resins into prepared cavities. Compactors, also referred to as amalgam condensers, provide the necessary pressure to ensure that the material is tightly packed within the preparation, which is crucial for the longevity and effectiveness of the filling. Proper condensation helps eliminate voids and minimizes the risk of microleakage, ensuring a better seal and enhancing the restoration's durability.

In contrast, excavators are primarily used for removing decay and debris from the tooth preparation and are not suitable for placing restorative materials. Spoon excavators have a similar function, focusing on the removal of soft dentin and debris but are not typically utilized in the placement process. Scalers, on the other hand, are designed for supragingival calculus removal and have no direct application in placing amalgams or composite resins. Therefore, compactors are the optimal instruments for this task due to their design and intended use in handling and placing restorative materials effectively.