😱 Have you heard about Dental Paresthesia? Discover its signs, symptoms, causes, and treatment before you’re at risk! The Oral Surgery DC Team
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.
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).
A person’s risk generally correlates with the positioning of their tooth.
A) The tooth’s roots may lie in close proximity to the primary nerve running through the jawbone (see illustration).
B) Or the position of the tooth may be such that surrounding soft tissues must be incised and reflected back so adequate access can be gained. If so, the prominent nerve running through these tissues may be traumatized or even severed.
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.
(Smith 2005) [reference sources]
What creates injection nerve trauma?
The irritation or damage caused may be due to:
- 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 are 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.
- 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 anesthetic that’s been injected may cause localized chemical damage to the nerve.
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.
(A diminished sense of feeling is termed “hypoesthesia.” The total loss of sensation is referred to as “anesthesia.”)
- 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 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.
- 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).
- Some people may experience “dysesthesia” (the feeling of painful or unpleasant sensations).
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.
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.
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.
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 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.
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 is indicated. But we can report that studies (Deshpande 2013, Kositbowornchai 2010) have shown 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 similar in how a dentist’s clinical skills are an important factor in reducing their patient’s risk for paresthesia (discussed next), a dentist’s experience in interpreting the telltale signs to be discovered on 2-D radiographs would be expected to be an important factor too.
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 / Clinician skill.
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.
A research paper by Jerjes (2010) 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.
Clearly, this is a primary reason why a general dentist will refer wisdom tooth extractions they anticipate will be challenging and thus lie beyond their skill level to an oral surgeon.
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.
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 planing 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 (2007) found 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).
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.
At this rate, it’s been estimated that during the course of their career a dentist will have 1 to 2 patients develop this complication. (Smith 2005)
How long does paresthesia last?
In most cases, a patient’s paresthesia will resolve on it’s 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.
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 full recovery.
(This classification refers to cases where the patient’s condition lasts longer than 6 months.)
Pogrel (2007) 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.
b) As related to dental injections.
In 85 to 94% of cases, spontaneous complete recovery typically occurs within 8 weeks.
Symptoms lasting more than 8 weeks are less likely to fully resolve.
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 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.
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.
Of course, in most cases the nature and extend 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.
Establishing a baseline for comparison.
Testing / mapping the affected areas.
As a way of documenting the extent of a patient’s condition, both initially and as recovery occurs, the affected area should 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, 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.
After the results of a person’s initial testing has been documented, comparisons can then be made periodically to evaluate the patient’s progress towards returning to normal.
Some sources suggest that evaluations should be conducted every 2 weeks for 2 months. Then every 6 weeks for the following 6 months. After that, every 6 months for 2 years, followed by yearly evaluation as long as full recovery has not occurred. (Smith 2005)
Surgical repair. / Microsurgery.
In cases of persistent or permanent paresthesia, surgical repair may be possible.
It’s difficult to know what to report in terms of what’s considered the best timing for the nerve’s attempted repair. It’s best said the a decision to attempt a repair, and subsequently the timing for it, depends on the nature of the sensory loss experienced (full, partial, recovering, etc…) and therefore best evaluated by the doctor (oral-maxillofacial surgeon, neurosurgeon or micro-neurosurgeon) who will provide the treatment.
- Surgery is frequently delayed until a point 6 to 12 months after the original injury, so to allow time for a repair to occur on its own if it will.
Some studies however (see below) seem to report that prompt repair increases the chances of case success.
- It may be that in situations where it is positively known (visualized) that the nerve has been cut that proceeding promptly with a repair attempt makes the best plan.
- Surgery may be attempted even much later on. The studies we cite below report surgeries having been performed multiple years following the patient’s original injury, although we don’t know the outcome of these cases.
Microsurgery success rates.
A paper by Pogrel (2007) 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 (2006) 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 surgical repair was attempted was 6.6 months following the patient’s initial injury.
- Bagheri (2012) 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 (2010) 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.
Much less information exists about the surgical repair of paresthesia resulting from dental injection. In some cases, long-term drug therapy is used to help these patients manage their condition.