Dental Injection and Complications: What You Should Know

Most people are aware that dental treatments require a local anesthetic injection to eliminate pain, but they may not fully understand the possible side effects that occur during or after the treatment process. Complications may occur in and around areas of the injection site and last anywhere from a few days to a few weeks. This article explains both common and rare side effects, their symptoms, and what can be done to prevent or manage them.

Issues related to Injection

Patients may experience burning sensation during the initial shot of anesthesia and it is one of the most commonly experienced symptoms. Burning sensation may probably occur due to the nature of the anesthetic medication or even when there is a temperature variation in the injecting liquid. It is usually mild and lasts until the duration of the shot, and resolves once the numbness sets in. Notify your doctor immediately if the sensation is unbearable so that he/she can act promptly before any internal tissue damage occurs.

Needle breakage, though exceedingly rare, may occur in scenarios where there is sudden movement during injection. When a patient moves quickly or suddenly, the broken needle fragment may fall out or even get trapped within the zone of injection. Patients are always advised to remain still during anesthesia administration and refrain from panicking when there is an incidence of breakage.

Persistent Anesthesia

Duration of anesthesia after the treatment is generally expected to last a few hours after the treatment and the effect fades off gradually within a few hours. But there are instances where the numbness can last longer than 24 hours of treatment due to trauma to the nerve by needle. This condition is called paresthesia where an entire region or a portion of the injected area (eg. part of tongue or lips) remains sensationless even after the numbing effect weans off. In some cases, there might also be abnormal increase in sensitivity to external stimuli like a hot or cold drink.

As a further complication, patients may unknowingly bite these areas due to lack of sensation and that may lead to unknown self-inflicted injuries. This condition mostly resolves in a few days but in some cases, it might last even up to six months. Rarely does it last longer than a year, but if it does, it is highly recommended to consult with an oral surgeon or neurologist. This complication commonly occurs when your dentist attempts to numb a portion of your lower jaw/teeth where part of your tongue, lower jaw skin, and lower lip get involved.

Restricted Mouth Opening (Trismus)

Tissue damage during needle prick or irritation caused by the injecting liquid are primary causes of restricted mouth opening after anesthesia. Repeated injections to achieve the numbing effect for a longer period during procedures can lead to this complication where one may not be able to open the mouth fully due to pain, swelling, and stiffness. It usually starts resolving one week after the procedure but in some patients, it might take up to 6 weeks or longer. Your doctor may suggest warm saline rinses or heat therapy in addition to pain killers and muscle relaxing medication to soothe the inflammation.

Swelling

There are several reasons for swelling to occur, and the exact root cause must be ruled out by a dentist to treat it appropriately and prevent further complications. A swelling with or without discoloration may appear during treatment when there is internal bleeding in the injected area, due to blood vessel damage. But it largely depends on the location of injection; some areas may suffer blood vessel injury, but they may not become swollen due to the thickness of the surrounding tissue. These swellings may be managed by the dentist at the time of treatment, by applying pressure. Swellings that occur after an extraction or root canal treatment are managed by applying cold packs to reduce inflammation and it is generally expected to subside within a week or two.

Another important type is the allergy-induced swelling, commonly known as angioedema. It happens when a person is allergic to anesthetic medication, and one may develop swelling in the eyelids, lips, tongue etc. This condition can even become life-threatening. In addition to providing anti-allergy medication, the doctor ensures that the patient is breathing, the respiratory pathway is clear of obstruction and consciously responsive.

Facial Nerve Paralysis

Although rare, this condition occurs when the medication liquid gets deeply injected into the salivary gland containing the facial nerve responsible for movement of facial muscles/features. After injection, the impacted facial nerve can temporarily lead to spasm of one side of the face, and the patient may not be able to close the eye on the affected side or control movement of facial muscles on this side. This complication is temporary, and its effects last only for a few hours. No medication or treatment is recommended as it usually resolves on its own without side effects.

References

1. Malamed, S. F. (2004). Handbook of local Anesthesia. Elsevier Health Sciences.

2. Malamed, S. F., DDS. (2018, September 13). Complications in local anesthesia. Dimensions of Dental Hygiene. https://dimensionsofdentalhygiene.com/article/Complications-in-Local-Anesthesia/#:~:text=Usually%2C%20the%20biggest%20problem%20in%20dentistry%20is%20when,which%20can%20lead%20to%20complications%20following%20the%20injection.

3. Angioedema. (2025, July 10). Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/22632-angioedema

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