As expressed in Part I of this article, an anterior-only appliance is an excellent choice for patients with muscle pain because it reduces muscle activity levels in clenching and excursions in most patients.
However, it does have two risks: developing an anterior open bite from anterior intrusion/posterior eruption and developing an anterior open bite from the mandible repositioning itself into a more retruded position. This is a continuation of the discussion on repositioning.
Who is at risk of mandibular repositioning? In my experience two different types of occlusions are at the highest risk for mandibular repositioning.
- Patients with extreme anterior shifts from their seated condylar position to their habitual intercuspal occlusion. I measure this shift on new patients at the initial exam, anytime the anterior shift is 3mm or more, I believe there is a much higher risk for mandibular repositioning.
- Patients with multiple bites. Anytime you ask a patient to bite and they respond by asking you, which bite do you want, or I don’t know where to bite, you have a very poorly defined intercuspal position and I believe a risk of mandibular repositioning with appliance therapy.
What do you do if this happens? First, make models and see if they hand articulate well. If they do, but the patient can’t get their occlusion to fit, you have a patient who has experienced mandibular repositioning.
Figures 6 and 7 above show a patient who only has occlusal contacts on her second molars, yet her models articulate perfectly except for the deciduous maxillary canine. Her repositioning isn’t from appliance wear; it is from degenerative joint disease that results in exactly the same appearance.
You now effectively have two choices if a patient repositions following appliance therapy. You can remove the appliance and hope the patient returns to their old occlusion, or continue appliance therapy to assure the muscles are relaxed and determine how to close the open bite. Typically the second option is the best because it will provide a stable mandibular position to create the new intercuspal position. As to how the open bite is closed, it may be through posterior equilibration or restorative, orthodontics, often intruding posterior teeth using implant anchorage, or potentially orthognathic surgery.
Having covered the primary risks of using an anterior only appliance to manage muscle pain, I would conclude by adding that anterior bite planes have been the most common appliance I have used for almost 35 years to treat patients with muscle pain, and in that time have experienced less then 10 open bites because of the appliance.
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