Active plates for treating positional anomalies can be fabricated in the maxilla and mandible and worn simultaneously to achieve the treatment objective. The dentitions are separated by occlusal guards so that the retentive components and active springs are not inadvertently activated and do not interlock or buckle during occluding. This offers the opportunity to join two appliances together for correcting an occlusal discrepancy. Elastics can be fitted to remedy a prognathic or retrognathic mandible. One appliance is firmly fixed in the maxilla, based on the principle of maxillomandibular anchorage, to correct the occlusal discrepancy in the opposing jaw by traction (Fig 10-60).
Guide planes for protrusive or retrusive movement are placed horizontally when the appliances are moved against each other with a screw. One of the two plates has no fixed retentive components so that the mouth can be opened when the appliance is being worn.
Guide planes can be attached to the anterior region or placed in the posterior region. Anteriorly placed, they are held angled downward and backward for protrusive movement; if retrusive movement is to be achieved, they are worked so that they slope upward and forward. With the mouth closed, the appliances slide into the desired position as if on an inclined plane. If a spring loop is now incorporated into an appliance within the guide plane, it can be bent out in order to be activated, and the malposition is gradually guided back to a state of equilibrium. When correcting an occlusal anomaly, correction of the dental arch form is necessary if the opposing occlusion is not harmonious in the corrected position because the dental arch is too narrow or too wide for the new position. This is when a double-plate comprising active appliances proves very beneficial, because adjustment of the dental arch can be achieved during occlusal correction.
For practical purposes, occlusal records of the desired position are taken (forced occlusions); if that is not possible, the desired position is established by hand. The models are mounted in a fixator in the appropriate position.