The normal range of jaw opening is between 40 and 50 mm. The initial 25 mm of opening is primarily achieved by rotation which occurs in the bottom half of the joints between the mandibular condyle of the jaw bone and the underneath surface of the disk. The remaining 15 to 25 mm is gained primarily through the forward gliding (anterior translation) motion that occurs between the upper surface of the disk and the temporal bone of the skull. Most people who suffer from TMJ hypermobility open beyond 50mm, and might experience what we call an “eminence click”. It can occur on one side or both, and is sometimes confused as being a disc displacement with reduction.
There is a pretty simple screen I use to assess if someone has systemic hypermobility when they see me for an evaluation. I look at excessive mobility in their elbows, knees, thumbs, pinky finger and lower back. I follow the Beighton 9 point scoring system. However, for those of you at home, the below questions have been shown to have pretty good accuracy to assess systemic hypermobility, and possibly you also suffer from TMJ hypermobility.
- Can you now or could you ever place your hands on the ﬂoor by bending forward with your knees straight?
- Can you now or could you ever bend your thumb to touch your forearm?
- As a child did you amuse your friends by contorting your body into strange shapes or could you do the splits?
- As a child or teenager did your shoulder or knee cap dislocate on more than one occasion?
- Do you consider yourself double-jointed?
Answering “yes” to any two questions indicates the presence of hypermobility with a high degree of accuracy. The sensitivity and speciﬁcity were 84% and 87%, respectively.
(Data from Beighton et al. and Hakim and Grahame.)
It has been found that 79% of patients with systemic hypermobility and clenching/grinding of teeth (or nail biting) go on to develop a TMJ problem. A control group with clenching/grinding but WITHOUT systemic hypermobility were found to have only a 16% chance of developing a TMJ problem. (Rocabado)
This is something that can definitely be managed very well with proper physical therapy and I have excellent success with. In my future blog post I will include some basic exercises you can at least do at home to limit some of the stress and dysfunction to your TM joints and hopefully prevent further progression of your condition.