Using EMG in Evidence Based Dentistry

I get a lot of people lately asking, "What is an EMG?"

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, and in Biometrics and Evidence Based Dentistry, we will be discussing surface EMG.

Why do we use EMG in dentistry? Simply put - to quantify rest. Using more biometrics based equipment in the dental office and diagnostical equipment can help dentists answer a lot of previously unknown questions in their cases.

We can measure EMG activity to evaluate muscle activity in function, such as chewing and biting, or to evaluate parafunctional activities (literally - 'outside' function, or abnormal function) such as clenching. EMG can also be used simultaneously with mastication (chewing) analysis and a computerized occlusal (bite) device.

During most EMG tests, the muscles that are being measured are the Anterior Temporalis (area above your ears towards your eyes), Masseter (cheek area), Digastrics (under the chin), and the Sternocleidomastoid (a support muscle in the neck). In evaluating rest, it can be noted if the muscles are hyperactive. If muscles are hyperactive, it may be indicative that the condyles are posteriorized, the mandible or lower jaw is posturing in a certain direction, or if there may be an issue with head and neck posture.

Where EMG becomes highly important and accurate is in the evaluation of function and parafunction. One example of a functional application 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.

Clenching is known as parafunction because it does not 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. By looking at the timing of when muscles fire and the amount of force, we can get an idea of how much force is being introduced into the system.

EMG tests can also give us prognostical data. Putting in a splint or an appliance can give us immediate feedback to see if we are improving muscle function or reducing overall muscle activity. As opposed to "hope dentistry" where dentists try a device and "hope" it works, it makes sense to use evidence based dentistry and a biometrics measurement to know the immediate impact we are having on a person when we make a "nightguard" or other appliance.

Someone's bite, or "occlusion" can be measured simultaneous to their muscle firing through EMG recordings and a link to computerized occlusal analysis. 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, or chewing. 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 a dental accident waiting to happen!

EMG is one of a number of biometrics tests that occur in the modern evidence based dentistry practice.