Anatomy
In the human brain, 12 paired and roughly symmetrical cranial nerves emerge from the back of the brain and travel through the head and face, providing nerve function (nerve innervation) to muscles, bones, and other tissues. Nerve innervation in the face comes from the facial nerve (the seventh cranial nerve) and the trigeminal nerve (the fifth cranial nerve).
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The facial nerve provides motor innervation to the muscles that help us make facial expressions, while the trigeminal nerve is responsible for sensory innervation to the face and motor innervation to the muscles used in chewing. The branches of the trigeminal nerve further branch into different nerves to provide information from one or more of your fives senses. The alveolar nerve, which the mental nerve branches into, is one of them.
Structure
The trigeminal nerve has three sensory branches:
Ophthalmic nerve Maxillary nerve Mandibular nerve
The largest of these branches is the mandibular nerve, which is necessary for jaw movement as well as sensory innervation mainly to the jawline, lower lip, and chin.
It divides into four motor and sensory branches: the auriculotemporal nerve, buccal nerve, inferior alveolar nerve, and lingual nerve. The inferior alveolar nerve, which runs along the lower teeth, plays both sensory and motor roles.
The inferior alveolar nerve further divides into:
Mylohyoid nerve: Connects to muscles in the lower part of the faceDental nerve: Innervates molars and premolars in the lower jawIncisive nerve: Innervates the canines and incisors in the lower jawMental nerve: Plays a sensory role in the lower, forward part of the face
Location
The mental nerve is purely sensory and has a rather short course. It divides from the inferior alveolar at a small opening in the jaw bone called the mental foramen, which is just beneath the premolars. It passes through the foramen, and beneath a muscle at the corner of your mouth called the depressor anguli oris or triangularis, the mental nerve divides into three parts:
The first branch runs down to the chin. The second and third branches run upward to innervate the mucous membrane of your lower lip and gums.
All of these branches communicate with the facial nerve.
Anatomical Variations
The mental nerve has some slight variations to its course. While three branches are standard, some people have more while others have fewer.
Some people also have multiple mental foramina (plural of foramen), which cause the mental nerve to branch in different ways. These variations are believed to be influenced by age, race, and sex, and are more common in people with other structural abnormalities in their jaw or face.
Sometimes, before a procedure involving anesthesia of the mental nerve, doctors will use imaging, such as X-rays or computed tomography (CT) scan, to ensure they know where the mental nerve is. Other times, they’re able to find it simply by palpating (feeling) the area.
Function
The mental nerve serves a purely sensory function:
The first branch of the mental nerve provides feeling to the skin on your chin. The other two, as they run along the lower teeth, innervate the gums of your incisors and canines, as well as the mucous membrane and skin inside your lip (buccal mucosa).
As with all nerves, you have one on each side. In the case of the mental nerve, there can be some crossover function—meaning the nerve on the left may provide some sensation to the structures on the right, and vice versa.
The Mental Nerve’s Role in Surgery
The mental nerve most often comes into play in plastic surgery and dentistry. In plastic surgery, anesthesia of the mental nerve is common during surgical reconstruction of the chin. During some chin surgeries, it’s common for the patient to be awake, and a nerve block of the mental nerve prevents them from feeling what’s going on.
Surgeons may also use mental nerve blocks when working on the jaw or lower lip.
When dentists work on the front portion of your lower jaw, they may use a mental nerve block alone or in combination with a block of the inferior alveolar nerve or the incisive nerve.
Associated Conditions
The mental nerve is vulnerable to damage due to:
Accidents during some surgeries and dental procedures (though this is uncommon) Injuries to the jaw Dental problems Less often, metastatic cancer
It can also be caused by some diseases of the central or peripheral nervous systems, including:
Multiple sclerosis Diabetic neuropathy Sarcoidosis Sjögren’s syndrome Trigeminal neuropathy Lyme disease
Nerve injury can cause paresthesia (altered nerve sensation such as tingling or burning) or numbness. Numbness or decreased sensation in the chin and lower lip is sometimes referred to as numb chin syndrome, or mental nerve neuropathy.
While it’s often minor and doesn’t have a large impact on daily activities, numb chin syndrome can be a serious problem for some people, interfering with their ability to:
Eat and drinkSpeakKissShave or apply makeup
Treatment
The treatment for mental nerve damage depends on the cause and severity of the symptoms. It may not require any treatment. If it does, drugs that may be used include:
Corticosteroids Benzodiazepines Tricyclic antidepressants Anti-neuralgic medications
Some studies suggest that vitamin B complex or vitamin B12 may be effective treatments as well.
In some cases, surgery may be required.
