Conceptually, full coverage appliances decrease elevator muscle activity in excursive movements if they are designed with anterior guidance, but do not reduce elevator muscle activity during clenching since they have posterior occlusion.
These appliances have a reputation for being the “preferred” appliance since they cover all the teeth in one arch and have occlusion on all the teeth as well. Because of this they can be considered the “safest” appliance to go to since there is not the risk of posterior eruption or anterior intrusion that an anterior bite plane has, but there are a few things you need to know about them.
We've gone over how all occlusal appliances are capable of protecting teeth from tooth wear, but certain appliances can have different impacts on muscles and joints. If your patient is a clencher, a full coverage appliance will not provide reduced muscle activity during clenching. In fact, a patient can clench harder on the appliance than they can on their teeth because the vertical is slightly open. However a full coverage appliance that has anterior guidance can reduce muscle activity when the patient is going through excursions.
Full coverage appliances can also allow the lateral pterygoid to release if you equilibrate the appliance with the condyle seated, if the appliance is not equilibrated this way the lateral pterygoid will not release fully since the appliance acts as a posterior interference. In addition a full coverage appliance can provide some support for joints that are symptomatic by altering the condylar position used to build the appliance and altering the anterior guidance, sometimes eliminating the guidance completely to provide support for the joints in excursions.
Like most appliances, there are some risks and a major contraindication with full arch maxillary appliances because some patients won't tolerate wearing them. Often times, patients can be sensitive to wearing a full-coverage device especially if they are required to wear it during waking hours.
You can create a lower full-coverage appliance, known as a full arch mandibular, that will take care of the same issues as an upper full-coverage appliance, but makes it easier to wear during the day and doesn't affect speech as much as the upper appliance. Also, there is always the risk that your patient's symptoms do not improve.
There are certain joint issues that can't be effectively treated with a full coverage appliance designed with a traditional occlusal schemes, and also patient's with muscle pain from clenching may not get any relief from a full coverage appliance.