What Is Lockjaw?

Woman with jaw pain.
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If you think that lockjaw is actually tetanus, you would have the same misconception as many people. Lockjaw is actually a misnomer for tetanus, as it is the name of one of the symptoms that may be experienced if you have acquired tetanus. The actual name for lockjaw is trismus, and is associated with a variety of health issues related to the head and neck.

What Is Lockjaw?

Lockjaw refers to the condition of having difficulty opening your mouth due to spasms in the muscles that you use for chewing (mastication).

You can most likely open your mouth somewhere between 40-60 mm or 1.5 to 2.3 inches. While the distance you open your mouth isn't enough to diagnose lockjaw, if you are experiencing lockjaw, you may only be able to open your mouth less than 35 mm (1.4 inches).

A good way to look for a restricted mouth opening is to try the  three finger test.

  1. Place your index, middle, and ring finger together.
  2. Turn your three fingers so that they are vertical
  3. Try to place your three fingers between your front teeth.

If your fingers fit between your front teeth comfortably, then you most likely do not need to be concerned with trismus.

How Common Is Lockjaw?

With vaccinations, the incidence of tetanus has declined, and in the United States from 2001 to 2008, there were only 233 reported cases. While rare, lockjaw is a common symptom experienced if you have tetanus.

However, if you have had treatment for cancer of the head and neck (surgical or radiation) you stand a 5 to 38 percent chance of developing lockjaw.

Improved techniques in both surgical and radiation therapies are helping to improve the incidence of lockjaw. Temporomandibular Joint (TMJ) disorders can also result in lockjaw in as many as 86 percent of the cases.

Other Symptoms Associated with Lockjaw

While the most common symptom related to lockjaw is the inability to open your mouth fully, there are several other symptoms associated with the condition.

These include:

Treatment for Lockjaw

Early intervention is very important if you are experiencing lockjaw. Procrastinating treatment can result in contractures which are rigid and deformed joints that will not function appropriately. Common therapies include dental treatments, physical therapy, tools or devices to assist in range-of-motion. If you are experiencing difficulties talking or swallowing, you should also have speech therapy.

The most common and effective treatments for lockjaw are tools or devices that assist you in improving range-of-motion. These can range from using your own fingers to assist in opening your mouth to devices that continually open and close your jaw according to the parameters which you can set. Manually opening and closing your mouth using your fingers is the least effective method for treating lockjaw.

The continual passive motion (CPM) machines are the most costly of the devices. These machines are programmable to operate within the range that you specify. It is recommended that you use these machines for 4-6 hours a day for 4-6 weeks, as determined by your physician or physical therapist.

A very inexpensive tool is a tongue depressor. You can insert tongue depressor blades stacked on top of each other until you have a comfortable stretch. You gradually can then increase the number of tongue depressors that you use to gain a stretch. While this method is considered "old-school" studies still show that it has benefits over some other methods.

The method that seems to have the best support is the TheraBite. While still costly (around $400-$600), it has been shown to improve mouth opening by 1-1.5mm per week up to about approximately 10mm. A common practice with the TheraBite is to open and close the mouth seven times, holding for seven seconds. These exercises are then repeated seven times a day for 10 weeks. This is commonly referred to as the 7-7-7 protocol.

It is important to never push the exercises to pain, stretching to the point of pain is counter-productive in treating lockjaw.


Bensadoun, R.J., Riesenbeck, D., Lockhart, P.B., Elting, L.S., Spijkervet, F.K.L. Brennan, M.T. (2010). A systematic review of trismus induced by cancer therapies in head and neck cancer patients. Support Care Cancer 18:1033–1038. DOI 10.1007/s00520-010-0847-4

Centers for Disease Control and Prevention. (2011). Tetanus Surveillance --- United States, 2001--2008. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6012a1.htm.

Kamstra, J.I., Roodenburg, J.L.N., Beurskens, C.H.G., Reintsema, H. & Dijkstra, P.U. (2013). TheraBite exercises to treat trismus secondary to head and neck cancer. Support Care Cancer. 21(4): 951–957. doi: 10.1007/s00520-012-1610-9

Walker, M & Burns, K. (2006). Trismus: Diagnosis and Management Considerations for the Speech Pathologist. http://www.asha.org/events/convention/handouts/2006/1200_walker_melissa/

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