Oral paresthesia: Nerve damage as a complication of wisdom tooth extraction.

- What is it? | Who's at risk? - Statistics. | Signs and symptoms. | Testing, recovery, treatment.

What is oral paresthesia?

Paresthesia is one possible postoperative complication associated with wisdom tooth removal.

It involves a situation where tissues or structures in or around the mouth (lip, tongue, facial skin, mouth lining, etc...) have altered sensation due to nerve trauma that occurred during oral surgery. This damage might be the result of bruising, stretching, crushing or even severing the nerve.

How dental anatomy plays a role.

A person's potential for experiencing paresthesia has to do with the position of their tooth in their jaw, in relation to the location of surrounding nerves.

Illustration showing close proximity of a wisdom tooth's root and mandibular nerve.

If a nerve lies relatively close to the tooth, or in surrounding tissues that must be manipulated during the extraction process, the potential exists that it may be traumatized as the tooth is removed.

What causes the trauma?

The nerve damage that occurs can be caused by:

  • The tooth itself as it touches against the nerve.
  • The instruments (forceps, elevators, drills) used to remove the tooth or the bone tissue around it.
  • The instruments used to retract the soft tissues surrounding the extraction site during the procedure.

Which nerves are usually affected?

Most cases of paresthesia occur in conjunction with the removal of lower 3rd molars (wisdom teeth) and, to a lesser extent, 2nd molars (the next tooth forward in the jaw).

The nerves that frequently lie in close proximity to these teeth (and thus are at risk for damage during the extraction process) are:

  • The mandibular (inferior alveolar) nerve. - This nerve runs the length of the lower jaw. It lies in the center of the jawbone at a level near the tip of the roots of the teeth. Towards its end, it gives rise to the mental nerve that branches out and runs to the lower lip and chin area.
  • The lingual nerve. - This is actually a branch of the mandibular nerve. It runs on the tongue-side surface of the lower jaw and services the soft tissue that covers it. It also branches to, and provides sensory perception for, the tongue.


Signs and symptoms of paresthesia.

Signs.

Paresthesia is a sensory-only phenomenon and not accompanied by muscle paralysis.

In most cases, the nerve damage is not identified during the surgical process but instead as a postoperative complication.

Symptoms.

The patient will notice altered, diminished, or even total loss of sensation in the affected area. One or more senses may be involved (taste, touch, pain, proprioception or temperature perception).

The precise area affected is that service by the damaged nerve. In the case of the mandibular or lingual nerves, that means some aspect the person's lip, chin, mouth lining or tongue.

Other characteristics.

  • For some people, the sensation may be tingling or numbness, similar to the feeling they experience when having a tooth anesthetized for a dental procedure. The difference being that the sensation persists.
  • While muscle function is not affected, the sensory changes experienced can be difficult to deal with. They may affect speech or chewing function, or interfere with activities such as playing a musical instrument.
  • The patient's quality of life may be significantly affected.

How long does the numbness/sensory loss last?

For those patients who are affected, one of 3 scenarios will play out.

  • In most cases, the paresthesia is transient, resolving on its own after just a few days or weeks.
  • With some cases, the condition is best classified as being persistent (lasting longer than 6 months).
  • For a small number of cases, the loss is permanent.

See below for details and statistics.


Evaluating a patient's risk for paresthesia.

A) Location, location, location.

As discussed above, one primary risk factor for paresthesia is simply the proximity of the tooth being extracted to nearby nerves (and therefore increased likelihood that they'll be traumatized during the extraction process).

X-ray image showing a good chance of dental paresthesia complications.

Identifying risk using x-rays.

In the case of the mandibular nerve, the dentist's pre-treatment x-ray evaluation of the tooth can give a hint as to what configuration exists.

The outline of the canal inside the jawbone that houses the mandibular nerve can usually be seen on x-rays. And its apparent closeness to the roots of the tooth planned for extraction can be evaluated.

One difficulty with this technique lies in the fact that the typical x-ray image is just a 2-dimensional representation (a flat picture) of a 3-dimensional configuration. And for this reason, only an educated guess can be made about the precise relationship that exists.

A more definitive picture can be gained using 3-D imaging, such as a Cone Beam CT scan. This technology is becoming more and more commonplace in the offices of oral surgeons, and even some general practitioners.

Risk and impaction type.

A tooth's precise orientation in the jawbone plays a role in paresthesia risk in two ways: 1) Tooth-nerve proximity. 2) It can greatly affect the surgical difficulty (and thus level of trauma) associated with removing the tooth.

As general rules:

  • Any lower wisdom tooth that's angled or positioned toward the tongue-side of the jawbone places the lingual nerve at greater risk.
  • Lower full-bony impactions, especially horizontal and mesio-angular ones (pictures), are the type of extraction most likely to result in trauma to the mandibular nerve.

B) Surgical factors.

Research has demonstrated that: 1) The dentist's level of experience, 2) The surgical technique they use, and 3) The amount of time they require to complete the extraction process - will each play a role in the patient's risk for experiencing paresthesia.

This is a primary reason why general dentists refer wisdom tooth extractions they anticipate will be challenging to an oral surgeon.

X-ray image showing how full root formation can make an extraction more difficult.

C) Age as a risk factor.

After the age of 25, a person's risk for experiencing paresthesia is generally considered to increase.

Relatively "older" patients (those over the age of 25, and especially over the age of 35 years) usually have wisdom teeth that have more fully formed roots and denser surrounding bone. Both of these factors tend to increase the difficulty of performing the tooth's extraction, and thus raise the level of trauma involved.

This is one reason why asymptomatic full-bony impacted wisdom teeth that show no sign of associated pathology are often left alone in people over the age of 35.

Paresthesia statistics.

In a review of research studies evaluating paresthesia after wisdom tooth extraction, Blondeau (2007) [reference sources] found reported incident rates ranging from 0.4% and 8.4%.

One large study (Haug 2005) evaluated the outcome of over 8,000 third molar extractions. It found an incidence rate of less than 2% for subjects age 25 years and older (as mentioned above, an age group that's relatively at-risk for this complication).


How long does paresthesia last?

In most cases, a patient's paresthesia will resolve on it's own over time. This can, however, take several months to over a year. In some cases, a person's sensory loss is permanent.

Spontaneous recovery.

In cases associated with wisdom teeth, Queral-Godoy (2005) found that most recoveries took place within the first 3 months. At 6 months, one-half of all of those affected experienced a full recovery.

Persistent paresthesia.

This state is typically classified as altered sensation that lasts longer than 6 months.

Pogrel's (2007) review of studies evaluating complications associated with wisdom tooth removal found reported incidence rates of persistent paresthesia ranging between 0% and 0.9% for the mandibular nerve and 0% and 0.5% for the lingual nerve.


Treating permanent paresthesia.

For those who experience persistent or permanent paresthesia, surgical repair may be possible.

In most cases, this attempt is not taken until 6 to 12 months after the original injury (so to allow time for a repair to occur on its own, if it will). The surgery can, however, be performed at an even later time frame.

Repair success rates.

Reported results for surgical intervention vary widely (Pogrel, 2007). Success rates appear to range between 50 and 92%, however some reported successes only involve partial recovery. Even if just partial recovery was achieved, many patients considered the attempt worthwhile.

Testing / mapping paresthesia.

As a way of documenting the extent of a patient's condition, both initially and as recovery occurs, the affected area can be mapped.

To do so, different types of sensory tests are performed, and those regions (lip, facial skin, tongue, etc...) that respond with no or altered sensation are recorded.

The mapping may include:

  • Light Touch - A small cotton ball is brushed against the skin to see if it can be felt. Moist tissues (like the lining of the mouth) can be difficult to evaluate.
  • Pin Prick - Areas are prodded with a pin or other sharp-pointed tool. The patient is asked if they can feel a sensation, and if so whether it feels sharp or dull. A comparison to the same location on the patient's unaffected side is made also.
  • Two-point Discrimination - A device having a series of paired sharp points, each a different distance apart, is systematically touched to the affected area. The patient is asked if they are able to feel its contact as one or two individual points.
  • Taste stimulation - Cotton balls soaked in saline (salt), sugar (sweet), vinegar (sour) or quinine (bitter) solution are drawn across the side of the tongue to see if a taste response is triggered.
 

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