Which dental cement is classically described as radiolucent, potentially obscuring radiographic diagnosis?

Silicate cement, an older (now largely obsolete) anterior restorative cement, was notably radiolucent on radiographs, which could mimic or mask underlying pathology such as recurrent caries — a classic point of dental radiology trivia. Amalgam is strongly radiopaque, and modern composites/RMGIC are formulated with radiopacifiers specifically to avoid this diagnostic problem.