Objective:To analyze the effect of painless anesthesia instrument in relieving the pain during the treatment of acute pulpitis of molars. Methods: 100 patients of acute pulpitis of molars were collected randomly. According to the treatment order, the first 50 patients underwent traditional injecting anesthesia and used to be the control group. The last 50 patients underwent injecting anesthesia with STA painless anesthesia instrument. Primacaine Adrenaline were used as anesthetic drug in both the two groups...