Screening for TMJ Dysfunction With Range of Motion Rulers

The American Dental Association (ADA) suggests that your dentist is the recommended professional to screen for TMJ dysfunction to his or her ability, and one of the quickest ways to screen for this dysfunction is to take a range of motion measurement of jaw opening.

Since the TMJ is the skeletal foundation of the craniofacial and masticatory system, a dysfunctional jaw joint can have adverse effects on the stability of the teeth and facial muscles.

Modern dentists have many ways that they can screen for TMJ dysfunction, including but not limited to:

  • Imaging (x-rays, MRI, CT scans)
  • Joint Vibration Analysis
  • Doppler
  • Auscultation (stethoscope)
  • Manual palpation
  • Medical history

A quick test that dentists may use to screen for TMJ dysfunction is to take a range of motion measurement. This is done using either a small range of motion scale ruler, boley gauge, or an orthodontic ruler.

What the dentist is looking for is to see if there is any restriction to opening the jaw. Like other joints in the body, the TMJ should be able to move freely without restriction. When there is dysfunction, like a restricted movement for example, it could signify that there is either a muscle problem or a locked jaw.

Locking Jaw

Dentists refer to a closed-lock jaw to the situation when the joint “disc” is stuck in front of the joint head (condyle), thus restricting movement upon opening. A range of motion scale measurement will show limiting at maximum opening. Typically, you should see a maximum opening of 40mm, or about the width of 3 fingers.

A limited range of motion in the jaw may suggest that there is a locked jaw, but it does not always mean that this is the case. As suggested, a limited range of motion can denote a muscle dysfunction, commonly seen in people who clench their teeth a lot and have sore facial muscles.

Dentists also use range of motion rulers to measure the distance that the jaw can move side-to-side. Known as lateral excursions, measuring the distance that the jaw can move side-to-side can tell the dentist if there is an issue with the jaw joint moving in and out of the proper position.

If the right jaw joint is dysfunctional for example, there may be issues moving the jaw to the left side. Abnormal chewing patterns using jaw tracking technology can also identify if there is dysfunction in either joint during masticatory movements.

Even with the abundance of advanced technology available for dentists, many will screen patients quickly at the exam with the aid of dental range of motion rulers.