Which restorative material is MOST radiolucent on radiographs?

Methyl methacrylate (acrylic resin) is the most radiolucent dental material — it has an attenuation coefficient similar to soft tissue, making it essentially invisible on radiographs. This can make it difficult to detect on periapical films. PMMA (polymethyl methacrylate) is used for denture bases and temporary crowns. Some composites now contain radiopaque fillers (barium, strontium) to improve radiographic visibility, but PMMA has no such additive.