A numb tongue can be the result of lingual nerve damage during dental treatment. The nerve for sensation to the tongue is called the lingual nerve.
On the other hand, a numb lip or chin will usually be the result of inferior alveolar nerve damage. Sometimes it is caused by damage to the mental nerve, which is just under the gum between the two lower premolar teeth. It can feel like a numb mouth, although it affects just one side of the lower lip.
In routine dental procedures, it is very unusual for a numb tongue or a numb lip to be totally permanent. At times, it may take up to 18 months for complete return of normal sensation, but most cases need less than this.
This is due to the fact that nerve injuries during dental treatment rarely result in the nerve endings being separated by more than a millimeter or so. When the endings are close together like this, they can regenerate.
This is a very different situation to when nerves are damaged in some kind of major accident, involving power tools or a car smash.
When can this damage occur? The two most frequent procedures are during the removal of an impacted wisdom tooth, and the surgical placement of a dental implant in the lower jaw to replace a back tooth.
During impacted wisdom tooth removal, the tooth to be removed is usually buried under the gum. The lingual nerve for the tongue runs just under the gum next to the wisdom tooth, on the inside where your tongue rests against the gum.
To remove an impacted tooth, some bone around the tooth has to be removed before it can be taken out. During this procedure, the possibility of nerve damage resulting in a numb tongue will always at the forefront of the surgeon's mind.
He will protect the nerves around the tooth by using retracting instruments to hold the gum away from where he is working. However, it is still possible for the retracting instruments themselves to press on the lingual nerve during removal of the tooth. Rarely, the nerve may be injured more severely by cutting tools.
This will cause a numb tongue on the affected side. The degree of numbness, and how long it lasts, both depend on how badly damaged the lingual nerve is.
A lower wisdom tooth also normally sits just above the inferior alveolar nerve, which supplies your lower lip. Quite often, the nerve will lie right across the root tips. As the tooth is being removed, it is possible for the nerve to be compressed or crushed.
This will cause a numb lip and chin on the affected side. Again, the degree of numbness, and how long it lasts, both depend on how severe the nerve injury is.
During dental implant treatment, it is quite rare for the lingual nerve to be affected, because it lies to one side of the jawbone, in the gum next to your tongue. Getting a numb tongue from dental impalnt surgery is unusual.However the inferior alveolar nerve lies in the middle of the lower jawbone. When an implant is put in, it is possible for the tip of it to press on the nerve.
What sort of damage can occur?
A dental nerve can be affected in one of four ways:
1. Compression. It is possible for a nerve to be compressed, either between two instruments, or by an implant pressing down.
If the compression only lasts for a short time, (ie. a lingual nerve being trapped by a retractor), any numbness should wear off within a few weeks. A dental implant, however, will need to be "unscrewed" slightly or removed completely within 48 hours, to relieve the compression on the nerve.
The decision whether to remove the implant completely or whether to just back it out slightly depends on how severe the numbness is, and how quickly you get back to the surgeon.
If you go back to him within 24 hours with just a tingling sensation in your lip, he may choose to just back it up slightly. But if you go back to him with a numb lip and it's been more than, say, 30 hours, then he will probably want to take the implant out completely. Numbness of the lip and chin should then resolve within a month or so.
2. Crushing. This is the same as above, but more severe. Again, the numbness should wear off, but will take longer. Perhaps several months.
3. Partially severed. If the nerves are partially severed, there will be an initial complete numbness, followed by a gradual return of sensation. There will probably be a residual numbness like "pins and needles" that could take a long time to wear off, perhaps 12 months or longer.
4. Completely severed. If the nerve is completely severed, the numbness of your lip and chin on that side will be total. It will feel absolutely "frozen".
However, if the nerve endings are close together (as they usually are) then it is possible for some regeneration to occur. You will get some feeling back over a period of time.
Occasionally an oral surgeon may attempt to repair the damage by repositioning the nerve endings. This may encourage regeneration of the nerve. The only problem is, the success rate for this procedure is highest if it is done within 3 weeks of the nerve injury. But we need to wait longer than that to get an idea of how severe the problem is!
Monitoring a numb area by "mapping". Your dentist or surgeon can monitor a numb lip and chin by mapping the exact area affected. This involves gently touching the skin with a pointed instrument, to detect the exact border between normal sensation and numbness.
The borderline is marked with a fine water-soluble marker all around the edge of the affected area, and then photographed.
This is repeated every one or two weeks, and the photographs compared. It should be possible to see a gradual reduction in the size of the affected area.
It is very reassuring to the patient to see documentary evidence of improvement! It's more difficult to map a numb tongue, because it's hard to keep your tongue still, and the marker keeps getting rubbed off. But it IS possible!
A numb tongue or a numb lip are recognised as normal risks associated with lower wisdom tooth removal or implant placement in the lower jaw.
The important thing is that your dentist or surgeon has discussed this with you, to make sure you are fully aware of the risks. They should also ask you to sign a consent form, which confirms that you understand the risk of getting a numb tongue or a numb lip, as well as the benefits and alternatives.
If you end up with lingual nerve damage or inferior alveolar nerve damage as a result of dental surgery, and you were NOT warned of the possibility beforehand, you may have grounds for a dental malpractice claim.