Almost every week I get a question on fixed mandibular advancement appliances (FMAA). More and more clinicians, orthodontists and GPs are using them. We see more and more Herbst, Forsus, Advance-Sync and recently I even saw X-Bows.
I regroup those FMAA under the group of ‘’hyper-propulsors’’. How can you evaluate a new hyper-propulsor that is presented to you? First, let’s make it clear that the dental arches do not have a single clue of what is holding them forward when you are using an hyper-propulsor. The teeth, group of teeth and the dental arches only ‘’feel’’ the anchor points, the amplitude and direction of forces applied in regard to the center of rotation and the resistance or anchorage designed in the appliance. In regard to the anchorage built into the appliance, the hyper-propulsors will have side effects of different grading : an headgear effect only on the upper molars or on the entire upper arch, a flaring effect on the lower incisors, a forward displacement of the condyles that may not necessarely be stable on the long term.
We have to keep in mind that the side effects are not always beneficial for a particular patient. The worst effect is probably the flaring of the lower incisors that will necessitate more advanced mechanics to bring them back to proper torque if the case needs it. In conclusion, remember that the effects produced by hyper-propulsors are more dento-alveolar than skeletal. They must not be blindly used on all our Class II patients without proper diagnosis and treatment planning.