Dental paresthesia: Nerve damage as a complication of wisdom tooth extraction or dental injection.

What is paresthesia?

Dental paresthesia is a possible postoperative complication associated with the removal of teeth (most frequently lower wisdom teeth), or in some cases receiving a dental injection.

(This condition can also be a post-op complication of root canal treatment or dental implant placement but that is not the focus of our coverage here.)

Causes - The onset of paresthesia is a result of nerve trauma. It involves the situation where during the patient's procedure a nerve lying in the immediate area has received some type of insult.

In most cases, the event involved has crushed, bruised, stretched or otherwise irritated the nerve. Less likely, it may have actually been nicked or severed.

Signs and Symptoms - As a result of the traumatic event, the person experiences a change in, or loss of, sensation in the tissues and structures that are serviced by the nerve. The lip, facial skin, tongue and lining of the mouth are all commonly affected areas.

Outcomes - The altered state typically persists for an extended period (days, weeks, months), ultimately resolving on its own without specific treatment. In some cases, the change in sensation that's noticed may be permanent, or only partially resolves.

Details.

As mentioned above, dental paresthesia may be a complication associated with tooth extraction or receiving a dental injection. We discuss each situation separately:

a) Paresthesia as a complication of tooth removal.

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

Tooth roots lying in close proximity to the Inferior Alevolar nerve.

Which nerves are usually affected?

The major nerves that lie in close proximity to 2nd and 3rd molars (wisdom teeth), and thus are at risk for receiving trauma or damage during the extraction process, are:

• The Inferior Alveolar nerve. - This nerve runs the length of the lower jawbone in its Mandibular canal (a tunnel-like structure through which the nerve and associated blood vessels run).
  

  The canal lies more or less in the center of the jawbone, at a level lying just below the roots of the teeth it holds (when they are fully erupted, thus explaining why the roots of impacted teeth tend to lie close to this nerve, see illustration above).

  At a point near its end, the Inferior Alveolar nerve gives rise to a branch called the Mental nerve. It exits the jawbone and runs to and services the tissues of the lower lip and chin region. (If the Inferior Alveolar nerve displays symptoms of paresthesia, this branch will too.)

• The lingual nerve. - This nerve runs through the soft tissues that cover over the inside surface of the lower jaw. It provides services for these tissues, and also branches off to and provides sensory perception for the tongue.

What can cause nerve trauma that leads to paresthesia?

Nerve bruising or stretching can result in significant levels of nerve irritation. Compressive forces may physically crush the nerve. Less likely, the nerve may have been partially or even completely severed.

• Compressive forces might be generated by the movement of the tooth as it's loosened up or removed, or by the extraction instruments being used. (An explanation of how teeth are removed.)
• The dental drill or hand instruments used to remove bone tissue or section the tooth during the extraction process may nick or sever the nerve.
  
• To gain access to the tooth, a gum tissue flap may need to be created. During events associated with incising and/or retracting this tissue, the nerve that lies within it may be traumatized or even severed.

b) Paresthesia associated with dental injections.

Other than surgical procedures, some cases of paresthesia are caused by routine dental injections.

Which nerves are most often affected?

The greatest risk of paresthesia lies with injections given to numb up lower back teeth. This is termed an inferior alveolar nerve block injection.

• The lingual nerve. - This is the same nerve mentioned above that runs through the soft tissues that cover the inside surface of the lower jawbone. 70% of cases involve the Lingual nerve.
• The Inferior Alveolar nerve. - This is the nerve mentioned above that runs through the jawbone's Mandibular canal. However, as related to injection paresthesia, the location at which the nerve is traumatized is prior to its entry into the bone (at a point during which it courses across the inside surface of the posterior jawbone).
  
• The Maxillary nerve. - While rare, this nerve that services aspects of the upper jaw may be affected.

▲ Section references - Smith

What creates injection nerve trauma?

The irritation or damage caused may be due to one or a combination of the following:

• Direct trauma caused by the needle itself.
  

  The largest gauge needle used in dentistry has a diameter of .45mm. In comparison, the size of the nerves that lie at risk is on the order of 4 to 7 times larger (on the order of the size of a spaghetti noodle).

  For this reason, a nerve receiving a nick is the most likely event, as opposed to being severed completely.

• Hydrostatic pressure.
  

  The process of injecting a local anesthetic into soft tissue may result in the creation of pressure that compresses/traumatizes adjacent nerve fibers.

• Hematoma formation.
  

  The movement of a needle through soft tissues may rupture blood vessels, thus causing the release of blood. Constriction of the hematoma (swelling of clotted blood) that then forms may place pressure on nerve fibers that pass through it.

• Neurotoxicity of the anesthetic. - The nature of the anesthetic used may cause localized chemical damage to the nerve.
  

  Some studies suggest that local anesthetics used in dentistry as more concentrated solutions (such as 4% prilocaine or 4% articaine) are more frequently associated with the development of paresthesia than lower concentration formulations (such as 2% lidocaine).

▲ Section references - Garisto

Signs and symptoms of paresthesia.

Paresthesia is a sensory-only phenomenon (meaning symptoms involving muscles, like paralysis or spasm, are not involved).

In most cases, the nerve damage is not identified during the dental procedure itself but instead first noticed as a postoperative complication during the hours following.

Paresthesia - Signs and symptoms.

• The person experiences an altered, diminished, or even total loss of sensation.
  

  [While on this page we tend to use the word paresthesia as an all-encompassing term, most precisely it refers to experiencing abnormal sensations. This might include tingling, numbness or a "pins and needles" effect (similar to the feeling a person experiences when they have a tooth anesthetized for a dental procedure).

  In comparison, a diminished sense of feeling is termed "hypoesthesia." The total loss of sensation is referred to as "anesthesia." Some people experience "dysesthesia," the feeling of painful or unpleasant sensations.]

• The extent of the affected area reveals the region serviced by the damaged nerve(s), and hence which are involved. Inferior Alveolar nerve = lip, chin. Lingual nerve = tissue lining on the inside of jaw, tongue.
• One or more sensations may have been affected: touch, pain, proprioception, temperature or taste.
  
• The effects may affect a person's speech, chewing function or cause drooling. They may interfere with activities such as playing a musical instrument.
  

  Even when the effects experienced are just minor, they can be difficult for a person to cope with. Their quality of life may be significantly affected. Social interactions may be inhibited.

Other characteristics.

• For some people, the sensation they experience may be a persistent tingling, numbness or "pins and needles" effect (similar to the feeling they experience when having a tooth anesthetized for a dental procedure).

Characteristics unique to dental injection paresthesia.

On occasion, while receiving a dental injection a person may experience an "electrical shock" sensation as the needle makes physical contact with their nerve. (This would be most common with inferior alveolar nerve block injections, the type of "shot" used to numb up lower back teeth.)

Having experienced a shock is not necessarily an indication that paresthesia will occur but there is a relationship.

• As many as 15% of people who experience this sensation go on to experience some degree of paresthesia.
  
• 57% of people who ultimately do experience paresthesia did experience the shock effect.

▲ Section references - Smith

How long does the numbness/sensory loss of paresthesia 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 a short period, usually measured in one or two to several weeks.
• With cases lasting longer than 6 months, the condition is classified as being persistent.
  
• For a small number of cases, the loss (complete, partial or partially resolved) is permanent.

We discuss statistics and events associated with case progress and outcomes in greater detail below.

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).

Identifying risk using x-rays.

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

2-D vs. 3-D imaging

One difficulty associated with using x-rays to make this determination is that common dental radiographs are 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 determination can be made using the cross-sectional imaging possible with 3-D radiography, 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 too.

It does however come at a greater expense, both in financial terms and in the level of radiation the patient is exposed to.

Is 3-D x-ray imaging really necessary?

Only the dentist performing the patient's work can determine if this level of evaluation (and the added expense and radiation exposure it involves for the patient) is indicated.

We can report that studies (Deshpande, Kositbowornchai) have determined that traditional 2-D imaging can reliably provide a practitioner with a high level of information regarding the configuration that exists, especially when a multi-x-ray technique is used. But of course, it is not as definitive as 3-D imaging.

▲ Section references - Deshpande, Kositbowornchai

Risk according to 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.

• 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.

Clinician skill.

A research paper by Jerjes bluntly states that one of the main risks for developing permanent sensory loss as a complication of nerve damage experienced during tooth extraction was the surgical skills/experience of the operator.

▲ Section references - Jerjes, La Monaca

Oral surgeon vs. general dentist.

There are a number of procedural steps that can help to prevent nerve damage from occurring during lower wisdom tooth extractions. They include:

• Appropriate gum flap design, and careful manipulation. Minimizing the amount of bone removed from the back and tongue sides of the tooth. Sectioning the tooth into parts for easier removal. Making sure the path of tooth removal (as related to the curvature of its roots) is appropriate. Careful and appropriate socket debridement after the tooth has been removed. (La Monaca)

▲ Section references - Jerjes, La Monaca

C) Age as a risk factor.

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.

C) Dental injections.

The vast majority of cases of paresthesia resulting from dental "shots" involve those used to numb up lower back teeth (specifically inferior alveolar nerve blocks).

But as opposed to oral surgery where the patient's risk can be evaluated during their procedure's planning stage, there's no way for a dentist to anticipate beforehand which dental injections might result in this complication.

Paresthesia occurrence - Statistics.

a) As related to wisdom tooth extraction.

In a review of research studies evaluating paresthesia after wisdom tooth extraction, Blondeau found incident rates ranging from 0.4% and 8.4%.

One large study (Haug) 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).

b) As related to dental injections.

It's been estimated that roughly 1 out of 27,000 Inferior Alveolar Mandibular blocks (the type of dental injection used to numb up lower back teeth, and the one most associated with this complication) will result in paresthesia.

▲ Section references - Blondeau, Haug, Smith

How long does paresthesia last?

In most cases, a patient's paresthesia will resolve on its own over time, with the amount of time ranging from just a few days, to several months, to over a year. In some cases a person's sensory loss, complete or partial, is permanent.

Generalities about recovery.

A person's level of sensory loss, their potential for recovery (full or partial), and the timeline associated with it will all correlate with the type (nerve irritation, crushing, nicking or severing) and extent of the original injury. Unfortunately, these are factors that are usually unknown.

Experiencing altered or diminished sensation implies that the nerve is still at least partially intact, a situation that favors recovery. But the complete loss of sensation doesn't necessarily mean that the nerve has been completely severed. A nerve that's been crushed can display this same symptom.

a) As related to wisdom tooth extraction.

Spontaneous recovery.

In cases associated with wisdom teeth, Queral-Godoy 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 classification refers to cases where the patient's condition lasts longer than 6 months.)

Pogrel reviewed studies that had evaluated complications associated with wisdom tooth removal and found reported incidence rates of persistent paresthesia ranging between 0% and 0.9% for the Inferior Alveolar nerve, and 0% and 0.5% for the Lingual nerve.

Paresthesia recovery - General rules of thumb.

• If a patient's condition has not completely resolved within a two-month time frame, the probability of their having some degree of permanent sensory deficit increases (although full resolution may still occur).
  
• If some level of deficit still remains after nine months, it's unlikely that complete resolution will occur.

▲ Section references - Queral-Godoy, Pogrel, Bhat

b) As related to dental injections.

Spontaneous recovery.

In 85 to 94% of cases, spontaneous complete recovery typically occurs within 8 weeks.

Persistent paresthesia.

▲ Section references - Smith

What can be expected during recovery?

Signs of paresthesia resolution.

Recovery from paresthesia, just like with any type of healing, is a process. And for that reason, any progress toward returning to normal can be expected to be a gradual transformation over a period of time. However, as the statistics above indicate, the time frame involved can be quite variable, ranging from just days to many months, to over a year.

• As sensation in the area starts to reappear, the degree of detail it provides should sharpen over time, hopefully returning all of the way back to normal parameters.
• Since the nerve fibers that transmit different types of sensations have different structural characteristics, one type of sensation may make a quicker recovery than others. As examples, perceptions involving pain and temperature typically appear first (Strauss).
• As you might expect, the sooner the first signs of renewed sensation appear, the more favorable the chances are for complete recovery (see statistics above).
  
• It may be that no progress is experienced for a period of time (weeks, months), and then signs start to appear.

▲ Section references - Strauss

Why paresthesia recovery rates vary.

The most important determining factor in a person's rate of recovery (and also how complete their recovery will be) is the nature and extent of the insult/damage that the nerve has received. As simple examples:

• A nerve that is still structurally intact (like those that have been bruised, stretched or compressed) can be expected to make a quicker, fuller recovery than one that has been severed.
  
• Nerves that have been nicked, as opposed to completely severed, have the quicker, more-favorable prognosis.

• What's generally referred to as a nerve is actually a bundle of individual nerve fibers. And as such, some fibers may have received a different type or extent of trauma due to their location in the bundle.
  

  (Following on with the examples above, bruised fibers would be more likely to make a quicker, more complete recovery than those that had been outright severed.)

Of course, in most cases the nature and extent of what's occurred isn't known. And as such, developing any specific rules about patient recovery rates are simply impossible to make.

Treating permanent paresthesia.

a) Testing and mapping - Establishing a baseline for comparison.

An important aspect of managing and treating a patient's paresthesia involves documenting the type, degree and extent of the effect that has been realized.

Doing so is important not just in evaluating the patient's sensory recovery but also in determining when and what type of further treatment, including microreconstructive surgery, might be indicated.

Testing / mapping the affected areas.

The following sensory tests are frequently performed, and those regions (lip, facial skin, tongue, etc...) that respond with no or altered sensation are recorded. (Where possible, pencil marks outlining the extent of the affected area are placed on the patient's skin and photographed. The picture can then be compared to future mapping.)

• Light Touch - A small cotton ball is brushed against the skin to see if it can be felt and if the patient can discern the direction of the ball's movement. Moist tissues (like the lining of the mouth) can be difficult to evaluate with this test.
  
• Sharp vs. dull discrimination - 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 pair of calipers having a pair of sharp points is systematically touched to the affected area, using various distance settings. The patient is asked if they are able to feel this 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.

Testing frequency.

After the results of a person's initial testing have been documented, comparisons can then be made periodically to evaluate the patient's progress towards returning to normal.

▲ Section references - Smith

b) Treatment with medications.

The use of some types of drugs may be beneficial in the management of nerve-related injuries. But there doesn't seem to be a wide-spread consensus or recommendation in published dental literature regarding the specific medications or regimens used with dental paresthesia.

Considering that most cases of paresthesia resolve on their own, possibly practitioners don't feel, or understand, a need for additional treatment therapies. Some of those mentioned in dental literature involve:

Anti-inflammatory medications.

The idea associated with the use of this type of drug is to help control inflammatory reactions that occur with the injured nerve that will tend to impede its recovery (swelling of nerve tissues, disruption of the nerve's associated microcirculation).

Two different classes of drugs might be chosen for this purpose. In some cases, they might be used in conjunction with each other.

• Steroids - Examples include oral dexamethasone or prednisolone.
  
• NSAIDS (nonsteroidal anti-inflammatory drugs) - An example would be ibuprofen/Motrin.

▲ Section references - Juodzbalys

An example.

A paper by Juodzbalys mentions a regimen of 800mg of ibuprofen 3 times daily for 3 weeks as a treatment assisting with the recovery of paresthesia resulting from dental implant placement.

Even in cases where the patient's doctor deems this approach appropriate, and the medication is appropriate for the patient's use, side effects such as gastric irritation and ulcer formation may occur, especially with long-term use.

Additional benefits.

Some cases of paresthesia (especially those caused by dental injection) may be due to pressure/compression directed on the nerve by local swelling. If so, an anti-inflammatory approach would assist in controlling this etiology.

Adrenocorticosteroids.

The use of adrenocorticosteroids (a type of steroid compound produced by the human body) early on after the patient's injury may help to minimize some types of neuropathy from forming during the healing process, thus promoting a more favorable outcome. (Juodzbalys)

c) Surgical repair. / Microsurgery.

In cases of persistent or permanent paresthesia, surgical repair may be possible.

Potential candidates.

It's clearly best stated that a decision to attempt a repair, and subsequently the timing for it, depends on the nature of the sensory change experienced (full or partial loss, painful, recovering, etc...) and therefore best evaluated by the doctor (oral-maxillofacial surgeon, neurosurgeon or micro-neurosurgeon) who will provide the treatment.

As general rules regarding who might possibly make a candidate for surgical repair:

• Patients who experience anesthesia (complete loss of sensation) for 2 to 3 months with no improvement.
• Patients who experience paresthesia (altered sensation) for 4 to 6 months with no improvement for 2 months.
  
• Patients who experience dysesthesias (painful or uncomfortable sensations) for a minimum duration of 2 to 3 months.

▲ Section references - Juodzbalys

Timing.

Once again, it will be the nature of the patient's case that will determine when a repair might be best attempted. And that decision is best made by the doctor who will be performing the surgery.

As you'll see below, the possible timing for secondary repair (surgical repair made after the date of the patient's original injury) can vary widely, and it may affect the procedure's outcome. That suggests to us that the potential need for surgical repair should be discussed relatively early during the healing process so no window of opportunity that might have been an asset is lost.

• Surgery may be delayed until a point 6 to 12 months after the original injury, so to allow the healing process to continue to the point of its completion (no further improvement) before a decision is made.
  
• Some studies (see below) seem to have found that prompt repair increases the chances of case success. And in fact, it may be that the most favorable window for an attempted (secondary) repair lies at about three months after the original injury. (Juodzbalys)

• It may be that in situations where it is positively known (visualized) or highly suspected that the nerve has been severed that proceeding promptly with a repair provides the most favorable outlook.
  
• Despite what in hindsight might have been considered ideal for a patient's case, attempts made at a later time are thought to be capable of yielding reasonable results.
  

  (Notice that some of the studies we cite below report surgeries having been performed multiple years following the patient's original injury. We don't, however, know the outcome of these specific cases.)

Microsurgery success rates.

A paper by Pogrel reports that results for surgical intervention vary widely. 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 still considered the attempt worthwhile.

A sampling of findings reported by research studies:

• Strauss evaluated the outcomes of Inferior Alveolar nerve repair experienced by 28 patients treated by one surgeon.
  

  50% reported significant improvement in their condition, 43% slight improvement and 7% gained no benefit. The average wait period before a surgical repair was attempted was 6.6 months following the patient's initial injury.

• Bagheri evaluated the outcome of 186 Inferior Alveolar nerve repair surgeries performed by multiple surgeons. On average the surgeries were performed 10.7 months following the patient's initial injury, with the range being 0 to 72 months).
  

  It was determined that 81% of cases resolved favorably, resulting in either a functionally useful (partial) or complete recovery. The study noted a drop in case success for surgeries performed at a point 12 months and beyond the patient's initial injury.

• In an evaluation of 222 Lingual nerve microsurgeries performed by multiple surgeons, Bagheri reported 66% of cases experienced complete recovery, 25% functionally useful recovery and the remainder no or inadequate improvement.
  

  On average, the surgeries were performed 8.5 months after the patient's initial injury (range 1.5 to 96 months). The study noted that shorter intervals tended to improve case outcomes. It also found a significant drop in case success for surgeries performed at a point 9 months and beyond the patient's initial injury.

▲ Section references - Bagheri, Joudzbalys, Pogrel, Strauss

Update log -

02/06/2019 - Links to reference sources added.

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Topic Menu ▶  Wisdom Teeth (third molars).

• Wisdom teeth basics -
  
  • Which teeth are they? (pictures) | Impaction classifications. (diagrams / pictures)
  • FYI facts about getting your wisdom teeth out.
• Overview of valid reasons for 3rd molar extraction.
  
  • Pain / Tissue trauma / Cysts / Tumors / Root resorption of adjacent tooth.
  • Pericoronitis (infection surrounding a 3rd molar).
  • Other reasons: Tooth decay. / Gum disease.
• Reasons not to extract third molars.
  
  • Do wisdom teeth really need to be removed?
  • The fallacy of the 3rd molar/tooth crowding theory.
  • Using a wait-and-see approach with wisdom teeth.
• Extracting wisdom teeth -
  
  • Estimating surgical difficulty.
  • At what age should you have your surgery performed?
  • Conscious sedation techniques used with oral surgery.
  • Aftercare: First 24 hours. / Day after and beyond.
  • Wisdom tooth extraction costs (according to impaction type).
• Overview of common post-extraction complications.
  
  • Dry Sockets / Paresthesia (nerve damage)
• Related pages -
  
  • Topic: Tooth Extractions