What is the reason for the cupping lesions on the occlusal surfaces of posterior teeth?

"Cupping" (a concave defect at the center of the occlusal surface with surrounding enamel rim) is the pathognomonic sign of acid erosion. Gastric acid (pH Ôëê 1–2) dissolves the more mineralized enamel first, leaving a saucer-shaped dentinal crater. Attrition produces flat, matching wear facets; abrasion produces V-shaped cervical notches; bruxism produces flattened cusps with matching wear on opposing teeth. GERD points directly to erosion.