Background

Mostly, the buccal mucosa, lower lip, and the skin behind the jaw below mental foramen receive sensation from mental nerve. Unlike the incisive nerve that supplies premolars and other lower teeth this does not supply them.  

Therefore, the nerve block application of local anesthesia to the mental nerve is part of important procedures like dental operations and other restorations of lacerations to the lower lip and chin prevalent in emergency medicine. In comparison to local anesthetic infusion surrounding the laceration nerve blockade is less painful because it prevents deformation and tissue swelling that may result from local infiltration. It is unknown exactly what portions of healthcare workers utilize the mental nerve block, however it is utilized by the dentist, dermatologists, plastic surgeons, and emergency medical staff. There are two main techniques for performing the mental nerve block. These two techniques are adopted including the percutaneous technique and the intraoral technique. The intraosseous technique generally is less painful, however other clinicians prefer the extraoral method. 

Indications

This procedure is indicated in the following situations: 

1. Injuries to the lower lip, but especially when the wound crosses the vermillion border. 
2. Surgical excision of lesions or tumors on face. 
3. A laceration through the soft chin tissue extending from the lip anteriorly through the alveolar process and extending caudally to the mid-body of the mandible. 
4. Postherpetic neuralgia pain is reduced 

Contraindications

It is contraindicated in: 

1. Hypersensitive to local anesthetic 
2. Intolerable to intraoral injection 
3. Distortion in anatomy 
4. Patient is non-cooperative 
5. Patient is refusing 

Outcomes

This procedure offers excellent anesthesia for the soft tissues and skin of the lower lip and chin on the same side. In view of this, all members of the healthcare team should know the procedure and assisting in performing this procedure. Non-dentists must familiarize should become familiar with the intraoral approach to the mental block, as it has been shown to be less painful for patients compared to the percutaneous technique. 

Equipment

1. 5ml syringe 
2. Gauze pads 
3. Chlorapep 
4. Desired local anesthetic 
5. Ultrasound gel 
6. Enough light source 
7. Topical anesthetic 
8. Needle 25-27 gauge 
9. Gloves 

Patient preparation

The patient must be seated ideally or laid on supine with the head reclined against a firm surface. This stabilizes the head and prevents movement throughout the procedure. 

Patient positioning

Position the patient in a semi-reclining posture. Or, use an ENT/dental chair if it is available. 

Technique

Approach considerations 

This procedure involves inserting a needle into the mucosal fold of brain, usually between the first and second premolars. The needle should be inserted at the mucobuccal fold, with the foramen located around the apices of these teeth. The intraoral approach is generally less painful and may reduce discomfort. A short needle is used to minimize discomfort and the risk of complications. Before injection, the syringe is aspirated to check for blood vessels. The depth and dosage are carefully controlled to ensure adequate drug diffusion. Post-procedure instructions advise the patient to avoid biting their lip or cheek until the anesthesia wears off. 

Technical considerations

There are two techniques to perform a mental nerve block namely, intraoral and extraoral. These two methods were compared by Syverud et.al who concluded that the intraoral block with the application of topical anesthesia were less painful than that of the percutaneous injection. The procedures of the intraoral variety are better anesthetized via an intraoral approach, and skin anesthesia can be achieved with either and equal efficacy. 

Intraoral 

1. Identify the point of injection, apply anestehsia (topical) at the site for about a minute. 
2. Pull back the lower lip, and then puncture the premolar with a small-gauge syringe until it is about 1cm deep by placing the thumb slightly below the mental foramen. 
3. If the individual complains of parasthesia, take out the needle to prevent injecting into the foramen. Aspirate to make sure that the needle is not present in a blood vessel. 
4. Apply 1.5mL to 3mL of local anesthetic. 
5. Although the effectiveness of the anesthetic is comparable, it is often less painful for patients to get the injection slowly. 
6. Successful block is manifested by pinprick sensation in the chin and inferior lip with loss of light touch. 

Percutaneous 

1. Locate the mental foramen using left index finger. 
2. Clean the skin with a topical anesthetic such as isopropyl alcohol. 
3. A 27-gauge needle should be injected at the designated site, advancing it about 1cm towards the foramen. 
4. Aspirate to ensure that the needle is not in a blood vessel. 
5. If the patient complains of paresthesia, withdraw the needle to avoid injecting into the foramen. 
6. Administer 1.5mL to 3mL of local anesthetic. 

Ultrasound guided technique 

1. The linear ultrasound probe is placed transversely over the lower portion of the mandible at the level of the second premolar. Bone will be seen as a hyperechoic linear structure on the ultrasound image. 
2. Scan cephalad until a hypoechoic cleft is seen which is the mental foramen. This is normally below the second premolar. 
3. Aspirate and introduce anesthesia in a manner similar to the other blocks. 
4. It has been shown that the use of ultrasound guidance decreases the time of procedure and the number of needle passes. 

Complications

Complications for this procedure include: 

1. Intravascualr injection 
2. Needle fracture 
3. Neurapraxia 
4. Infection 
5. Bleeding. 

References

Mental Nerve Block – StatPearls – NCBI Bookshelf (nih.gov) 

References

Mental Nerve Block – StatPearls – NCBI Bookshelf (nih.gov)