Dentin can be regenerated. There is a layer of tissue similar to human stem cells on the inside of dentin, and when dentin is damaged, restorative dentin, or regenerated dentin, will appear after about 3 months of restoration. However, the regenerated dentin requires certain conditions, such as a calcium hydroxide base to help the repair, and avoiding stimulating the tooth with too cold or too hot water or food after filling, so that the dentin has a restoration period, and then new dentin will grow out. However, the new dentin is very slow and has certain conditions, if there is further bacterial attack, the regeneration of dentin will stop or even cause pulpitis.