Overview of Mental Nerve Block
The mental nerve is responsible for sensation in the lower lip, the inner cheek, and the skin on the lower chin, but not the lower teeth. These areas are instead served by the incisive nerve. For this reason, numbing the mental nerve through local anesthesia is needed for a variety of treatments, like dental work and stitching up cuts on the lower lip and chin, which are common in the emergency room.
Blocking the nerve this way is less painful than numbing the area around the cut, which can lead to distorted soft tissues and swelling. The mental nerve block method is widely used by many healthcare workers, including dentists, skin specialists, plastic surgeons, and emergency room staff. There are two ways to do this procedure as discussed in medical documents: needle insertion through the skin (percutaneous) or inside the mouth (intraoral).
Although the approach from inside the mouth tends to be less painful than inserting a needle through the skin, non-dental practitioners typically use the latter method.
Anatomy and Physiology of Mental Nerve Block
The lower branch of the trigeminal nerve, which is the nerve responsible for sensations in the face, exits the skull through a hole called the foramen ovale. Right after this, it forms two more nerves, one that goes to helps control a muscle in your jaw and another one called the nervus spinosus. The lower branch of the trigeminal nerve then splits into two other branches called anterior and posterior branches.
The anterior branch serves mostly to control movement while the posterior branch primarily deals with sense of touch and has three different parts: one for sensation in the area in front of the ear, one responsible for sensation in lower teeth and another one for the tongue. The nerve for the lower teeth module enters the lower jawbone through a hole called the mandibular foramen, passes through a canal inside the jawbone, and exits through, another hole known as mental foramen. Here, it changes its name to the mental nerve. The nerve continues inside the lower jaw to provide sensation for the back teeth, eye teeth, and front teeth.
The mental foramen, the hole through which the nerve for lower teeth area exits, is most often found about halfway along the lower edge of the jawbone, usually level with the second pre-molar tooth. However, its location can vary from person to person, which makes it difficult to say precisely where it is. Depending on perspective, it can be seen either toward the front or back of the roots of the pre-molar teeth and it could be located above, at, or below the tip of the roots. Factors such as gender, age, ethnicity, and what method is used to locate it (touch, X-ray, or CT scan) can all cause these differences. Additionally, if a person has lost their teeth, this can cause the bone around the area to recede, placing the mental foramen closer to the top edge of the gum [6]. However, several studies have shown that, despite these variations, doctors can successfully numb the area by locating the foramen using touch and other landmarks.
Why do People Need Mental Nerve Block
A mental nerve block is a medical procedure typically used when someone has a cut on their lower lip or chin that needs to be treated. This treatment helps avoid causing more harm to the area, like swelling or changes to the soft tissues, which can result from injecting medication directly into the injury. For procedures near the center of the lower jaw, a mental nerve block may be given on both sides. This technique can also be used in skin surgeries. In particular, it can be a good choice for older patients or those with several health conditions to calm them down during a specific form of skin cancer surgery known as Mohs micrographic surgery.
Dentists also use the mental nerve block technique either on its own or along with a procedure called an inferior alveolar nerve block. Research has shown that nearly half of all patients experience numbness in their first molars (the large teeth at the back of your mouth), between 82% to 100% experience numbness in the premolars (the teeth after molars), and almost 40% in the lateral incisors (the second tooth from the center of the mouth). The chances of successfully numbing this area increase if the medication is injected inside of a small hole or opening in the jawbone for the second premolar and canine teeth. Injecting the medication outside of this small hole or opening is usually successful for skin and internal mouth procedures.
When a Person Should Avoid Mental Nerve Block
A mental nerve block is a type of local anesthesia used for certain dental procedures. However, there are certain situations when it should not be used:
* If the patient is allergic to the drugs often used for numbing – these are called local anesthetics.
* If the patient has an active facial infection or an oral infection, like herpes infection or cellulitis (a bacterial skin infection), the block isn’t safe to use.
* Some people simply can’t tolerate getting an injection inside their mouth, and in such cases, they can’t have a mental nerve block.
Equipment used for Mental Nerve Block
For a procedure called a mental nerve block, certain tools are needed. This procedure is aimed at numbing a part of your face by blocking the mental nerve. Here’s what the doctor uses:
* A small needle (25 to 30 gauge or smaller) – Very thin needle to minimize any discomfort
* A small syringe (2 to 5 mL) – This is used to inject the numbing medicine
* Local anesthesia (with or without epinephrine) – This is the medicine that will numb the area
* Gloves – Used by the doctor to keep everything clean and sterile
* Topical anesthesia if the approach is through the mouth – This would be a numbing gel or cream
* Topical antiseptic if the approach is from outside the mouth – This is used to clean the skin where the injection will be given [7]
Preparing for Mental Nerve Block
It’s best if the patient is sitting or lying down during the procedure. Their head should rest against a firm surface. This position helps keep the head steady and prevents it from moving, which is important during the procedure.
How is Mental Nerve Block performed
There are two commonly used methods to perform a nerve block, which is a technique to numb a specific area. These methods are the intraoral (inside the mouth) and extraoral (outside the mouth, also known as percutaneous). In a study comparing the two, it was found that the intraoral method, particularly when accompanied by a numbing cream, was less uncomfortable for the patient than the extraoral method. Both methods, however, were equally effective in numbing the skin.
The extraoral method involves the following steps:
- Locate the mental foramen (a small hole on the jawbone) using the left index finger
- Clean the skin with an antiseptic like isopropyl (rubbing alcohol)
- Insert a thin needle (27-gauge) into the skin, aiming roughly 1 cm toward the foramen
- Pull back on the plunger of the needle before injecting to make sure you aren’t in a blood vessel (this is called aspiration)
- If the patient experiences a tingling sensation (paresthesia), withdraw the needle to avoid injecting into the foramen directly
- Inject 1.5 to 3 mL of the local numbing medicine
The intraoral method proceeds as follows:
- Determine where the injection site will be
- Pair a topical numbing cream on the injection site for about 60 seconds
- Pull down the lower lip and insert a small needle parallel to the premolar, about 1 cm deep, again being mindful of not going too far and entering the foramen
- As with the extraoral method, withdraw the needle if the patient has a tingling sensation and remember to pull back on the plunger to avoid injecting into a blood vessel
- Inject 1.5 to 3 mL of the local numbing medicine
Patients tend to feel more comfortable when the injection is done slowly, and both methods are usually successful at blocking the nerve. You can test the success of the nerve block by asking the patient if they feel a pinprick sensation or light touch on their lower lip or chin. A successful block means they won’t feel these sensations.
Possible Complications of Mental Nerve Block
To successfully numb the mental nerve before a procedure, a doctor doesn’t need to insert a needle into the mental foramen (a hole on the lower jawbone through which the nerve passes). If fact, doing so might raise the chances of permanent nerve damage or accidentally injecting medicine into a blood vessel. Instead, the safest method is an extra-foraminal injection, where the needle is inserted just outside of the foramen. This technique still effectively numbs the skin and soft tissues in front of the nerve.
What Else Should I Know About Mental Nerve Block?
Using a ‘nerve block’ to numb the mental nerve (a nerve located near the chin) as it comes out of the mental foramen (a tiny hole in the jaw bone) can very effectively numb the skin and soft tissues of the same side chin and lower lip. This technique is relatively straightforward, safe and can be easily taught. The benefit of using this method is that it can avoid the need for deeper sedation or the risk of tissue changing shape that may occur with other local numbing methods. This can be particularly useful for minor procedures in an outpatient setting, like emergency care, dermatology, or surgery.
