Tooth decay happens in five stages and can be prevented with good oral hygiene. In the first stage, the enamel loses minerals, which can be reversed with fluoride treatments. If untreated, it progresses to the second stage where cavities form, requiring fillings. In the third stage, decay reaches the dentin, causing sensitivity and possibly needing crowns. The fourth stage affects the pulp, often necessitating root canals. The final stage can lead to abscesses, severe pain, and may require tooth extraction. To prevent tooth decay, brush twice daily, avoid sugary foods, and visit your dentist regularly.