EMG stands for Electromyography. There are two types of EMG, surface EMG and
needle EMG. Surface EMG is generally
accepted as the gold standard for overall muscle function, whereas needle EMG is
more effective in nerve conduction experiments and biofeedback procedures. From this point on, I will be talking about
surface EMG.
Measuring EMG activity generally has 3 purposes….rest,
function, and parafunction. (We can also
evaluate muscle activity simultaneous to chewing and biting with mastication
analysis and T-scan). Generally, the
muscles measured in EMG are the Anterior Temporalis, Masseter, Digastrics (and
some supra-hyoid), and the SCM’s (Sternocloidomastoid). In evaluating rest, sometimes, it can be
important that muscles are hyperactive.
If muscles are hyperactive, it may be indicative that the condyles are
posteriorized, the mandible is posturing in a certain direction, or if there may
be an issue with head and neck posture.
In my opinion, resting EMG’s are highly, highly overrated, as the
information is much like acquiring a blood pressure. The data may change from one minute to the
next.
Where EMG becomes highly important and accurate is in the
evaluation of function and parafunction.
Function is evaluated by having the patient swallow. If activity is seen in the elevator muscles
(Temporalis and Masseter), it can be assumed that the teeth are touching when
the person is swallowing. However, if
there is no muscle activity, it can be assumed that there is some sort of tongue
thrust, which can be a mandibular posturing issue or airway issue. Swallows that are long in duration can also
be of significance and cause hyperactivity or spasms in the digastrics
muscles.
I really love the ability to see how the muscles are
functioning during a clench, we call this parafunction, because, clenching
doesn’t happen naturally, it is an activity that is usually induced by stress or
an airway issue. Some people even think
that it can be caused by a bad bite.
Looking at when muscles fire and with how much force can give us an idea
of how much force is being introduced into the system when someone clenches, and
how healthy the muscles are. Putting in
a splint or an appliance can give us immediate feedback as to if we are
improving muscle function or reducing overall muscle activity. It is my opinion that we should know the
immediate impact we are having on a person when we make a “nightguard” (or
whatever that is) or any type of appliance for someone.
Someone’s bite, or “occlusion” can be measured simultaneous
to their muscle firing through the T-scan/EMG link. This is extremely useful in restorative
dentistry and “occlusal equilibration.”
Knowing which tooth hits first, with how much force, and when the muscles
shut off makes for the most effective dentistry.
Muscles also play an important role in Mastication. If someone can produce a normal chewing
pattern, but has to do muscle gymnastics to do so, that is extremely useful
information because that is the exact patient who is an accident waiting to
happen! Next time, I will be covering
the use of T-scan to analyze a person’s bite.
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