Teeth crumbling with red spots (which may indicate deep decay or nerve exposure, such as internal resorption) require urgent evaluation by a dentist. There are no over-the-counter medicines or supplements that can rebuild crumbling teeth. You need a professional clinical exam and X-rays to determine if you need crowns, root canals, or fillings. To manage symptoms until your appointment, use a high-fluoride toothpaste or a remineralizing paste containing hydroxyapatite to protect the remaining enamel. Rinse with an alcohol-free antibacterial mouthwash to prevent infection, and strictly avoid acidic, sugary, or hard foods. Please schedule a dental visit immediately.