Mental Nerve Block


Article Author:
Danielle Betz


Article Editor:
Kathleen Fane


Editors In Chief:
Brian Downs
Ziad Katrib


Managing Editors:
Avais Raja
Orawan Chaigasame
Khalid Alsayouri
Kyle Blair
Radia Jamil
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Saad Nazir
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Sarosh Vaqar
Mark Pellegrini
James Hughes
Beenish Sohail
Hajira Basit
Phillip Hynes
Sandeep Sekhon


Updated:
6/1/2019 10:44:00 PM

Introduction

Local anesthesia of the face, mouth, and teeth is required for a variety of procedures. These include dental procedures and laceration repairs, along with several other surgical procedures. Facial nerve blocks are employed by dentists, dermatologists, plastic surgeons, and emergency room providers as a means of analgesia that is more comfortable than local infiltration, and that will not cause local tissue distortion. Local blocks can also negate the need for procedural sedation, which is particularly important in patients with multiple comorbidities. The mental and incisive nerves supply sensation to the lower teeth and skin of the chin and lower lip as well as buccal mucosa, making this nerve block useful for multiple procedures[1].

Anatomy

The third branch of the facial nerve, the mandibular nerve, splits into 2 branches, anterior and posterior. The posterior trunk has 3 branches, one of which is the inferior alveolar nerve which has sensory-only branches that traverse the mandibular canal to exit via the mental foramen. One of those branches is the mental nerve, which supplies sensation to the skin and buccal mucosa of the lip and the skin of the chin. The incisive nerve continues in the mandibular medullary cavity to the premolars, canines, and incisors.[1]

The mental nerve exits through the mental foramen bilaterally in the mandible. The mental foramen is typically located halfway between the upper (alveolar crest) and the lower edge of the mandible in direct line with the second bicuspid (premolar). Exact mental canal location, however, can be variable. In edentulous individuals, there is alveolar bone resorption which makes the location of the mental foramen closer to the alveolar crest in a majority of patients[2]. The location of the foramen has been found on a horizontal plane mesial, distal, or between the apices of the premolar roots. On a vertical plane, the foramen has been found above, at, or below the apex of the premolars. The variations are influenced by gender, age, race, and technique used for assessment (palpation, Panorex, CT). Given this variability, testing for anesthesia prior to the initiation of any procedure is important. Full anesthesia, however, has been demonstrated in multiple studies with localization of the foramen with palpation and landmarks alone.

Indications

Given the reliability and easy localization of the mental foramen, anesthesia of the mental nerve is particularly useful for dermatologic procedures. In the emergency setting, laceration repair of skin/buccal mucosa of the lower lip or chin can be performed without local injection, which can distort anatomy[1]. In most studies, all patients report lip numbness following mental nerve block. The technique can also be applied to dermatologic surgeries and has been used as an alternative to procedural sedation, which can be particularly risky in elderly patient or patients which multiple comorbidities[3]. Lacerations or surgeries near the midline may require bilateral mental nerve block.

Dentists use the mental/incisive nerve block either alone or in addition to an inferior alveolar nerve block[4]. Studies have shown that 47% of patients develop pulp anesthesia in the first molars, 82% to 100% develop pulp anesthesia to the bicuspids (premolars), and 38% of patient develop pulp anesthesia in the lateral incisors. There is a greater chance of success of incisive nerve block if the injection is given inside the foramen for the second bicuspid and the canine. There was no difference in the success of injection inside versus outside of the mental foramen in anesthesia of the first bicuspid.[5]

Contraindications

Contraindications to mental/incisive nerve block include:

  • Allergy to local anesthetics
  • Active facial or intraoral infectious lesions (herpes infection, cellulitis)

Equipment

  • Small-bore needle (25 to 30 gauge have been reported)
  • Small syringe (2 to 5 mL)
  • Local anesthetic (with or without epinephrine)
  • Gloves
  • Topical anesthetic if intraoral approach
  • Topical antiseptic if extraoral approach[3]

Personnel

This procedure can be done as a sole operator or with an assistant to retract the lower lip.

Preparation

The patient should ideally be seated or laying with their head placed back against a firm surface to stabilize the head and prevent movement during the procedure.

Technique

There are two described techniques for performing this nerve block: intraoral and extraoral (percutaneous). In one study, the intraoral approach with pre-application of topical anesthetic was shown to be less painful than the percutaneous approach[6].

Percutaneous

  • Identify the mental foramen (as described above in Anatomy)
  • Prepare the skin with topical antiseptic
  • Insert a small-gauge needle with a small syringe of anesthetic approximately 1cm toward the exit of the mental nerve from the foramen
  • Avoid intra-foraminal injection by withdrawing the needle if the patient reports paresthesias
  • Aspirate to exclude placement of the needle tip in the vasculature
  • Instill 1.5 to 3 mL local anesthetic*

Intraoral

  • Identify the mental foramen (as described above in Anatomy)
  • Retract the lower lip and apply a topical anesthetic to the base of the first bicuspid at the inferior labial sulcus for approximately 60 seconds
  • Insert a small-gauge needle with a small syringe of anesthetic to approximately 1 cm depth. This has been described as pulling the lip laterally, keeping the thumb placed just below the mental foramen as palpated previously. Then, direct the needle from the long axis of the second premolar in an anterior, inferior orientation
  • Avoid intra-foraminal injection by withdrawing the needle if the patient reports paresthesias
  • Aspirate to exclude placement of the needle tip in the vasculature
  • Instill 1.5 to 3 mL local anesthetic*

*Slow injection of anesthetic has been proven more comfortable to patients than brisk injection and anesthesia success is the same for rapid versus slow injection[5].

Complications

Needle entry into the mental foramen is not necessary for successful anesthesia of the mental nerve[7] and may increase the risk of permanent nerve damage. Dental providers have historically entered the foramen with improved anesthesia of the incisive nerve and anterior maxillary teeth. However, for anesthesia of the mental nerve, extra-foraminal injection is safest and still provides complete anesthesia to the skin and soft tissues anterior to the nerve.

Clinical Significance

Anesthesia via nerve block of the mental nerve just as it exits the mental foramen provides excellent anesthesia to the skin and soft tissues of the ipsilateral chin and the lower lip. This block is relatively easy to perform with landmarks, is safe, and is easy to teach operators. It can negate the need for procedural sedation or the risk of tissue distortion with local anesthetic in an outpatient emergency, dermatology, or surgical setting.

Enhancing Healthcare Team Outcomes

Nerve block of the mental nerve provides excellent anesthesia to the skin and soft tissues of the ipsilateral chin and the lower lip; as a consequence, all members of the healthcare team should be familiar with the procedure and assisting in performing this block. [Level V]


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Mental Nerve Block - Questions

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A 17-year-old kickboxer sustained a complex laceration (crosses the vermillion border) of the lower lip during a match. Which of the following anesthetic techniques would be best for the repair?



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A 17-year-old boy is skateboarding and has a fall, presenting to the emergency room with a deep laceration to his left lower lip. In preparation for placing sutures, the physician feels that performing a nerve block will be the most comfortable for the patient and facilitate the best cosmetic closure. What landmarks should the physician use to help anesthetize the area?



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A 24-year-old male presents to the emergency department with facial lacerations after a fistfight. He has multiple lacerations that need cosmetic repair, including lacerations to the upper lip, lower lip, eyebrow, and cheek. A mental nerve block is being considered. Which areas of the face will be affected by this block?



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A 17-year-old male presents to the emergency department after getting into a fight at a party. He has several contusions and lacerations to his face from sustaining punches, one of which is a through-and-through laceration to his lower lip which does not touch the vermillion border and is just right of midline. Which type of anesthetic and what technique are ideal for this laceration repair?



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A 17-year-old female fell and struck her chin on her coffee table, sustaining a 2 cm laceration to the right side of her chin. The plan is to repair the laceration and get set up for a mental nerve block. What is the anatomical location that should be used?

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Mental Nerve Block - References

References

A comparative study of the percutaneous versus intraoral technique for mental nerve block., Syverud SA,Jenkins JM,Schwab RA,Lynch MT,Knoop K,Trott A,, Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 1994 Nov-Dec     [PubMed]
The position of the mental foramen in dentate and edentulous mandibles: clinical and surgical relevance., Charalampakis A,Kourkoumelis G,Psari C,Antoniou V,Piagkou M,Demesticha T,Kotsiomitis E,Troupis T,, Folia morphologica, 2017 May 29     [PubMed]
Influence of injection speed on the effectiveness of incisive/mental nerve block: a randomized, controlled, double-blind study in adult volunteers., Whitworth JM,Kanaa MD,Corbett IP,Meechan JG,, Journal of endodontics, 2007 Oct     [PubMed]
Evaluation of the effectiveness and comfort of incisive nerve anesthesia given inside or outside the mental foramen., Joyce AP,Donnelly JC,, Journal of endodontics, 1993 Aug     [PubMed]
An evaluation of the incisive nerve block and combination inferior alveolar and incisive nerve blocks in mandibular anesthesia., Nist RA,Reader A,Beck M,Meyers WJ,, Journal of endodontics, 1992 Sep     [PubMed]
Regional nerve blocks of the face., Moskovitz JB,Sabatino F,, Emergency medicine clinics of North America, 2013 May     [PubMed]
Tan FF,Schiere S,Reidinga AC,Wit F,Veldman PH, Blockade of the mental nerve for lower lip surgery as a safe alternative to general anesthesia in two very old patients. Local and regional anesthesia. 2015;     [PubMed]

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