When the cotton is dislodged, it may cause secondary infection in the root canal causing pain, so it is recommended to go to the hospital in time to re-seal the medication after sterilization. Dental drilling cotton, often in order to temporarily seal the drug in the root canal, to eliminate the inhibition of bacteria in the root canal for the purpose, but when the cotton falls off, the oral saliva, food debris, bacteria will enter the root canal fermentation and reproduction, resulting in secondary infection in the root canal causing pain, the need to go to the hospital in a timely manner to clean the root canal disinfection and re-dose the temporary sealing. Tooth drilling and medication after cotton fall off, need to seek medical treatment as soon as possible to avoid causing inflammation or cause inflammation to expand the formation of periapical periodontitis exacerbate the pain.