The mental foramen is a small hole in the lower jaw. "Foramen" is a medical term for any kind of natural hole in the body's skeleton. Its purpose is to provide a passage which the mental nerve and other veins pass through to supply the tissues of the mouth. It is used as a marker by dentists and other surgeons when doing work so as not to cause damage to any of the facial nerves.
The mental nerve also passes through the foramina. It is a three-pronged nerve which allows there to be feeling in the face. It runs from the spine up the neck and goes through the mental foramen. From there, it splits into three branches: two into the lower lip and one into the chin.
Since the mental nerve goes through the mental foramen, it can be affected by any disorder on the part of the surrounding nerve. Any kind of chin or bone trauma can disturb the mental foramen, pinching the nerve to the face. The resulting numbness is referred to as "numb chin syndrome," a blanket term since it can have many different causes.
Numb chin syndrome can result from cancer in the bones of the jaw. It can also be caused by any kind of trauma to the mental foramen, which can cause the nerve to be pinched. Any sudden facial numbness needs to be checked out by a doctor.
The mental foramen is usually located in the lower jaw just below the second premolar tooth. There is one of these openings on each side of the jaw. These foramini allow for passage of blood vessels into the mouth and face. This position varies slightly by ethnic group and also in individuals without teeth.
There have also been cases where a person has been discovered to have more than one mental foramen during jaw surgery. This condition is extremely rare. It is important, however, for x-rays to be taken before any kind of jaw surgery because of this possibility.
Before receiving dental surgery, a patient will often receive a "nerve block," which induces numbness in the face through anesthetic. This is achieved through injecting the antiseptic locally into the flesh below the tongue. The mental foramen is used as a kind of marker for dentists before they do the injection. Using their fingers, they will locate the mental foramen through the skin and then use that to guide them so that they do not inject the mental nerve directly.