What Is A Mental Nerve Block?
The mental nerve is a lower jaw nerve that mainly supplies sensation to parts of the oral cavity and the orofacial regions of the lower jaws like the lower lip, the buccal mucosa, the skin of the chin that lies ventral to the mental foramen, etc. Mental nerve blocks are beneficial when excellent anesthesia is required during dental surgical procedures like intraoral or lower facial laceration surgeries and repairs. It excludes the lower teeth including the premolar region that is innervated by the incisive nerve. Hence, local anesthesia to the mental nerve is employed in various dental treatment procedures required in emergency room traumas like laceration repair surgeries of the lower lip or the chin region.
A nerve blockage is comparatively less painful than infiltration around the laceration site. Hence, the mental nerve block has the potential to prevent any soft tissue distortion and swelling that is otherwise generated by local infiltration. Many healthcare clinicians and maxillofacial surgeons routinely employ mental nerve block techniques. Even general dentists, dermatologists, plastic surgeons, and emergency physicians routinely use this technique as per need. The block is often used by plastic and dermatologic surgeons in cosmetic procedures, proving to be an effective alternative to sedation in elderly patients throughout the last decade.
What Is the Anatomic Course of the Mental Nerve?
The mandibular branch of the trigeminal nerve (third branch) follows its course within the cranium and exits through the foramen ovale after which it branches into two nerves- a nerve to the medial pterygoid muscle and a nerve to the nervus spinosus. The trunk of the mandibular nerve further splits into anterior and posterior branches. While the anterior branch is primarily responsible for motor innervation, the posterior branch, which is sensory, is categorized into three divisions: auriculotemporal nerve, inferior alveolar nerve, and lingual nerve. These are the three major nerves of the lower jaw or the mandible. The inferior alveolar nerve traverses along the mandibular canal and exits through the mental foramen as the mental nerve. The incisive nerve on the other hand continues in the mandibular canal innervating the lower premolars, canines, and incisors.
What Is the Location, Assessment, and Efficacy of the Mental Nerve Block?
The mental foramen is an identifiable mandibular landmark located halfway between the alveolar bone crest of the lower jaw and the inferior border of the mandible, in a straight line from the second premolar or between the two premolars. However, it is hard to determine the exact position of the mental foramen owing to the high variance in the horizontal plane. The foramen identifies the mesial, distal, or inter-root region of the premolar roots. On the vertical plane, the mental foramen is usually alongside or below the apices of the mandibular premolars. The variation in the location of the foramen may be influenced by the patient’s gender, age, race, etc, and also by the operator's assessment tactics and dexterity. Ideally, manual palpation is required prior to mental nerve block. Physiologic aging, certain pathologic changes, and systemic conditions like alveolar resorption, typical in edentulous individuals, make the foramen closer to the alveolar crest which might require the oral surgeon to order panoramic imaging and CBCT to accurately locate the foramen. Despite the variability of the location of the foramen, studies have shown that complete anesthesia is achieved by locating the foramen just by palpation or landmark identification.
Dentists may prefer to use the mental or incisive nerve block either exclusively or in adjunct to the inferior alveolar nerve block which still remains the most potent mandibular anesthetic technique. Studies have also shown that approximately half of the patients develop pulpal anesthesia of the first molars. However, the main target of this block is the premolars with 82 to 100 % efficacy which reduces to 40 % in the lateral incisors.
What Is the Technique of Mental Nerve Block?
The mental nerve block, particularly useful in treating skin-based lacerations of the lower lip and chin, is associated with potential complications based on operator technique. In this block, first, the location of the mental foramen is identified by the operator.
The procedure starts by inserting a 27-gauge needle parallel to the premolar at about 1 cm depth with the thumb placed just below the palpated landmark. Aspiration is done to prevent any vascular reaction or injection. Also, the intra-foraminal injection should be avoided by withdrawing the needle if the patient reports paresthesia. About 1.5 to 3 mL of local anesthetic solution can be injected slowly to produce an anesthetic effect efficaciously and painlessly. The dentist or medical operator should avoid injecting into the injured site which may result in post-operative anesthetic complications like edema or soft tissue distortion. Surgical procedures near the mandibular midline may also require the practitioner to give a bilateral mental nerve block.
Conclusion
The mental nerve block is a relatively safe, simple, and operator-dependent technique used to anesthetize the lower lip and chin by dentists, dermatologists, and plastic surgeons. This, ideally, requires preoperative assessment by the surgeon in order to identify the landmarks. This block can also be employed as an alternative to procedural sedation in cosmetic surgeries to reduce any tissue distortion that may occur with a conventional infiltration in an outpatient emergency or surgical setting.
