Most of the time when a dentist is going to work on a lower tooth he will administer a mandibular block. The signal that dentists use to determine whether a patient has achieved a mandibular block is a numb lower lip on the side of the injection. At that point the dentist usually believess the patient will be numb enough for the patient to feel no pain when a drlll touches the dentin of a tooth on that side of the mandible.
What should be done if the patients tooth still hurts when the drill touches it? Often a different type of injection should be used. Often intraligamental injections work when a mandibular block provides insufficient anesthesia. These injections are placed into the ligament surrounding a tooth and usually require a special type of anesthetic syringe that can deliver the solution with a higher pressure so that it can enter the ligamental space around a tooth.