Position and anatomical landmarks
Infiltration is carried out with the patient in the supine position with the head in a slightly backward flexion position. The head is positioned in the midline.
In adult patients, the second bicuspid tooth is located and the mental foramen palpated and marked. The distance between the mental foramen and the midline is about 2.5 cm (see figure).
The surrounding area is disinfected and covered with sterile drapes. A needle (22-G) is inserted perpendicularly (under ultrasound guidance) just medial to the mental foramen until there is contact with bone. The location of the nerve is confirmed when the patient experiences reproducible paresthesia in the chin by stimulation with 50 Hz, 0.5 V. Subsequently, a pulsed radiofrequency current of 45 V lasting for 120 seconds is administered with no preceding local anaesthetic. The maximum temperature should not exceed 42°C, but if this occurs the output should be reduced. If necessary, a second treatment period of 120 seconds can be administered if the impedance is above 500 Ω, prior to injection of 1 ml NaCl 0.9% solution.
- The most serious complication of the injection is infection.
- Small subcutaneous bleedings may result in a temporary increase in pain after the injection.