Many times I get asked if there is a connection between the vertical
dimension of an occlusal appliance and it’s effectiveness. The answer is
“yes” and “no”. There is scientific evidence that supports that the
activity of the elevator muscles decreases as we open the vertical
dimension of occlusion. The next questions to ask, are how the amount of
vertical change affects the amount of muscle activity reduction and the
duration of this affect. One of our goals in appliance therapy is to
reduce the activity of the elevator muscles. This reduction directly
affects the signs and symptoms associated with muscles, like headache as
well as having a positive impact in reducing joint loading which is a
percentage of the total force applied. With this in mind the fact that
the muscle activity of the elevator muscles decreases as we open
vertical dimension is most likely one of the reasons appliance therapy
works in helping our patients feel better. It may also contribute to
why during appliance therapy of short duration we see less evidence of
attrition. It may not be that the person has stopped or reduced the
amount of parafunction occurring, but that they are applying less force
and therefore not notching the appliance significantly.
Elevator
muscle activity decreases as we begin to open vertical, but beware that
at some point the force starts to rise again until we approach maximum
opening. The range of decreased activity seems to be more than 1mm of
opening and less that the patients vertical dimension of rest. The other
challenge to be aware of is that studies have shown this reduction in
elevator muscle activity to be transient, and that the body adapts and
the muscle force returns to baseline even at the new VDO. This
phenomenon means that we can not count on only the effect of changing
VDO to provide therapeutic benefit for our patients. Long lasting
benefits come from designing an appliance at the appropriate condylar
position and with the optimal occlusal design based on that patient’s
joint, muscle and dental condition.
Originally posted on www.leeannbrady.com