A review of the literature showed that the outcome of orthognathic surgery may differ from the planned outcome, that casts mounted on semi-adjustable articulators show systematic errors of orientation and that there may be a causal connection between them.
It was demonstrated that the movements of casts mounted on, and moved relative to, a standard articulator produced movements of different magnitudes relative to the natural head position. A mathematical model was developed to quantify the difference and the predictions of the resulting equations were confirmed in a photographic study using image analysis.
The second stage of the study compared a standard and the orthognathic articulator. Plastic model skulls were mounted at different angulations to represent different natural head positions. Casts of the maxillary teeth of the skulls mounted on the orthognathic articulator accurately reproduced the occlusal plane angles of the skulls, but those mounted on the standard articulator showed systematic errors of up to 28º. Surgical movements of the maxilla were reproduced using perioperative wafers constructed on casts mounted on the standard and orthognathic articulators. The accuracy of the maxillary repositioning was assessed at five anatomical reference points on the skulls. The results indicated that the orthognathic articulator was significantly more accurate than the standard articulator
