Oral Nerve Blocks
Clinical uses: graft harvest for hypospadias repair (buccal or lower lip graft); lower lip/chin surgery
Technique:
A landmark-based technique
25g needle
tongue depressor to help with exposure
Buccal Block
The needle tip is inserted into the coronoid notch region of the mandible in the mucous membrane distal and buccal to the most distal molar. After (-) aspiration, 0.5-1.0 mL of chosen local should be injected. Our surgeon typically harvests from the left buccal mucosa, so we routinely only block the left side.
Occasionally, a surgeon will harvest the mucosa of the lower lip. The distal branch of the alveolar nerve, the mental nerve, supplies the innervation for the lower lip mucosa. The addition of bilateral inferior alveolar or mental nerve blocks should suffice in this circumstance.
Inferior Alveolar Nerve Block
The needle tip is inserted at the medial border of the mandibular ramus about 1/2 cm above the mandibular teeth adjacent to the coronoid notch and the pterygomandibular depression. The needle is advanced until bone is contacted, then withdrawn slightly. After (-) apiration, the LA is injected. One may incidentally block the lingual nerve causing anesthesia of the anterior 2/3 of the tongue. If the needle is placed too medially the medial pterygoid muscle can be injected, resulting in trismus. If needle is positioned too posteriorly, anesthetic may be put into parotid gland, causing transient facial paralysis of the facial nerve with temporary loss of facial expression, inability to close the eyelid and the drooping of the labial commissure. These can be avoided by blocking the more distal branch, the mental nerve.
CN: Coronoid Notch, IA: Inferior Alveolar injection site; B: Buccal Nerve injection site; PTD: Pterygotemporal depression
Mental Nerve Block
Indications: lower lip/chin surgery; mental graft (mucosa of lower lip for hypospadias repair)
Nerve blocked: Mental nerve, terminal branch of the inferior alveolar nerve
Coverage: Skin of the ipsilateral inferior lip and chin
Technique: Palpate for the foramen along the external mandible. Retract the lower lip outward and downward and insert the needle at the junction of mucosa and gum, in line with the second premolar. Direct the needle inferiorly toward the mental foramen and inject LA near, but not in, the mental foramen. Repeat on the opposite side if the operative region crosses midline.
The mental nerve exits the mandible at the mental foramen. The mental foramen has many variations, not only in size and shape, but also in location and the direction of the opening. In an cadaveric study by Kqiku et al, researchers found the most common position of the mental foramen was between the first and second mandibular premolars in 38% of the cases and in line with the long axis of the second mandibular premolar in 28% of cases. However, for many of patients, especially for hypospadias, they have yet to get their first tooth. In children before tooth eruption, Gershenson et al found that the foramen is somewhat closer to the alveolar margin; during tooth eruption, the MF descends to roughly halfway between the margin.
Mental Nerve
Kqiku L, Sivic E, Weiglein A, Städtler P. Position of the mental foramen: An anatomical study. Wiener Medizinische Wochenschrift. 2011;161(9-10):272-273
Gershenson, A., Nathan, H. and Luchansky, E., 1986. Mental foramen and mental nerve: changes with age. Cells Tissues Organs, 126(1), pp.21-28.