Patient with crowns on maxillary incisors that repeatedly loosen. No caries. Most probable cause?

Correct answer: C. Lingual surface interference during protrusion

• A. Lack of ferrule would more likely cause tooth/root fracture or recurring decementation from inadequate resistance form, but the specific clinical pattern described (repeated loosening without caries) points more directly to occlusal interference.
• B. Inadequate cement is a generic possible cause but does not explain a recurring, specific functional pattern as well as an identifiable occlusal interference.
• C. Correct. Lingual surface (protrusive) interference creates repeated excessive lateral/shear forces on anterior crowns during function, a recognized cause of repeated decementation.
• D. Nocturnal bruxism alone, without addressing the interference itself, doesn't fully account for this specific recurring pattern as precisely as a protrusive interference.