Application of the model-positioning appliance for three-dimensional positioning of the maxilla in cast surgery.

During cast surgery the model-positioning appliance allows a controlled three-dimensional positioning of the maxillary incisors and of the entire maxilla in one- or two-jaw surgery. The model-positioning appliance is fastened, in place of the incisal pin or the incisal table, to the anterior end of the upper part of a semiadjustable articulator. Three reference points are marked with a pencil directly on three maxillary teeth. The reference plane during cast surgery is the hinge axis-infraorbital plane, which is represented by a parallel to the upper part of the articulator. All measurements during cast surgery are parallel or at a right angle to this reference plane. Three-dimensional adjustment of the maxillary cast is possible without measurements with a ruler and without the marking of reference points and drawing osteotomy lines on the base of the cast. Sawing cuts on the base of the cast corresponding to marked osteotomy lines is avoided. In this way errors are reduced and precision is increased. The advantage of model-positioning appliance is that the three reference points on the maxillary teeth can be adjusted simultaneously and that the relation of the whole maxillary dental arch to the mandibular dental arch can be controlled at the same time.