trismus after dental injection

Trismus is a painful condition that tends to restrict normal mandibular function and movement. Generally, all conditions which can lead to the inability of opening the mouth within a normal range of 35 to 55 mm (40 mm average) may be addressed as Trismus. Several factors are responsible for this condition, ranging from a disturbance of the trigeminal nerve to life-threatening conditions such as tetanus.

Extraction of wisdom teeth (lower third molars) might also cause Trismus as a result of inflammation in the mastication muscles area or direct trauma to the temporomandibular joint (TMJ). However, it’s important to note that Trismus is not synonymous with tetanus (lockjaw) although they are closely related. 

Can It Happen At The Dentist?

For the majority of dental practitioners, it is routine to administer local anesthetics almost daily. Normally, the anesthetic effect is achieved with no adverse effects. However, it is possible for complications, even serious ones, to happen.

Trismus can happen as a result of inflammation following dental surgery or due to jaw hyperextension during the procedure. This could be due to the prolonged mouth opening during the dental appointment. If the needle injecting anesthetic inadvertently causes damage to the surrounding tissues, Trismus could also result.

Several problems can arise that include difficulty speaking, problems eating and swallowing, and oral hygiene issues. Those patients who don’t get prompt treatment could end up developing Trismus and edema following dental surgery.

How Can It Be Avoided?

As noted above, Trismus is associated with jaw infections. Trismus complications after injecting local anesthetic are rare and they may be averted by using short needles when doing maxillary posterior injections. Additionally, avoiding multiple injections in a short span of time can help. 

If any indication of infection appears, it is important that it’s addressed quickly. This includes swelling, pain, redness, and warmth in the affected area. The prevention of infection can help in preventing Trismus from developing. The prevention can be through the early institution of diverse treatment such as heat, exercises, analgesics, and muscle relaxants.

How Long Does It Last?

The most widely seen complication associated with local anesthesia is persistent pain at the injection site. Trismus is, however, more of a temporary complication rather than a permanent one. Nevertheless, the earlier treatment is started, the better are the chances for a faster and greater recovery.

A mouth that cannot open fully, is the trismus hallmark. If you are unable to fit 3 fingers that are vertically lined up between the bottom and top front teeth it could be another sign of Trismus.

Treatment options include:

  • Using jaw-stretching devices
  • Medical muscle relaxants
  • Physical therapy – jaw massaging and stretching
  • Applying heat to the affected area
  • Soft foods until Trismus symptoms disappear.

Some patients suffering from severe Trismus may experience an element of muscle spasm that Botulinum Toxin injection can improve.


Most affected individuals will normally notice some relief from Trismus-associated pain after 48 hours, although cases have been reported lasting two weeks. The bottom line is that the earlier a person seeks and receives treatment, the better they can expect the outcome to be. Therefore, you shouldn’t hesitate to seek professional help straight away the moment you notice any of the symptoms associated with trismus. The prognosis, if treatment gets delayed, is certainly not as good.

Author: Peter Mayhew

Peter is a dental hygienist in the city of Chicago, IL. In his free time he likes to write blogs and product reviews on anything dental health related.