Tooth decay can be caused by oral hygiene and eating habits in life. To determine whether tooth decay is rotten to the nerve, it needs to be determined by the symptoms and certain techniques. When the tooth decay reaches the nerve, it will show the following symptoms: 1. When the tooth touches the irritating taste or temperature, such as acidic food, cold water, cold wind, and very hot food, the gum will feel painful, and the pain will last for a long time; 2. The tooth decay has been formed for a long time, and the cavity is deep; 3. When eating, it will be painful, and the cavity formed by the tooth decay will often be stuffed with food, and the pain will be relieved when the food is removed. The performance of the above three symptoms is the performance of tooth decay to the nerve. In addition, dental radiographs can be taken to clarify the degree of tooth decay and its specific location. After tooth decay appears, you should go to the hospital for treatment in time to prevent tooth decay from involving other teeth. Teeth are important and should be taken care of daily. Brush your teeth in the morning and evening, rinse your mouth after meals to remove the food residue on your teeth to avoid the formation of tooth decay; use toothpicks less often, as frequent use of toothpicks will make the gap between your teeth bigger and easily leave food, which is not easy to clean and will also cause your teeth to loosen; do not bite hard things, use your teeth correctly and go to the dentist for regular checkups.