Use of the Stuart Articulator in Obtaining Optimal Occlusion

Abstract

In the manufacture of jaw-writing devices, the first essential is a proper scribing mechanism. Wax-coated glass plates and sharp styluses were first used to make the writing records. The styluses were forced through the wax onto the glass tables by elastic loops. The inscriptions made in the wax on the tables were later etched by hydroflouric acid. More experimentation determined that such writing pens and inscription plates produced serious inaccuracies because of resistance. They were discarded because the wax offered resistance to the plowing motions of the styluses during the jaw movements made while setting the controls of the articulator. These sources of resistance made a “one-plus-one” addition of errors. This 200 per cent increase of inaccuracy could intervene enough to negate all needed accuracies in the steps taken to make a truthful counterpart of the moving relations of the jaws. The three principles of jawwriting devices are: they must be inflexibly attached to the jaws; the styluses must make their inscriptions frictionlessly; and the inscriptions of the writings must be capable of being made more permanent by a covering of transparent frictionless tape. Important comments on our findings are: pencils of graphite or ballpoint pens offer too much resistance against the inscription-receiving material of the tables; and the pressure contacts created by the elastic loops or springs necessary to make the inscriptions on the selected pad materials generate sufficient errors to make the data recorded little more than useless. Such inaccuracies do not help us reach our gnathologic goals. Other important features of the gnathokinographic facebow are as follows. (1) The inscription table should be on the maxillary arms and the magnetically controlled styluses should be on the mandibular arms of the jaw-writer in the condylar area. This provides a clearer understanding of the cranially oriented directions of the scribed lines of motion. When the scribers are fastened to the maxillary parts of the jaw-writing bows and the tables are on the mandibular, the written descriptions of the jaw motions are upside down and reversed from left to right and also from front to back. Dentist are often deeply confused about cusp and condylar paths because the engineers and the instrument designers place the pencils on the maxillary and the tables on the mandibular parts. (2) A jaw-writing device should have its writing styluses and recording tables near the condyles. They should be placed so that the inscribed records most nearly simulate the actual movements of points in the condyles which are inside the cranium. If they are put forward near the cheeks and nearly opposite the molars, the inscriptions then will simulate scribings of molars rather than those of condyles. Whenever possible the points of the styluses should actually be consciously selected points in the lateral extensions of the opening-closing axis of the mandible. The further the points of the styluses are set away from the opening-closing axis, the less they mimic the movements of the condyles. Gysi drew some weird conclusions about condyle “paths” because he misplaced his condyle tracers. 4 (3) Shortening the arms of the jaw-writer may carry the styluses too far forward and too near the median sagittal plane of the cranium. These two abbreviations reduce the magnification of the scribed lines. It reduces the magnification of the condyle motions which are surprisingly short to the inexperienced student. This reduces the accuracy capacity of the operator. A magnifying lens is needed to judge the sharpness of a photographic focus. One can state that an articulator is valueless if it is used with inaccurate casts, improper interocclusal records, and improper or insufficent jaw-writing records. Gnathologic results can be obtained only after many carefully taken steps. No perfection is absolute because some flaws creep in no matter how careful the dentist is. Perfection is the meticulous attention to detail, and as Michaelangelo noted, “Perfection is no trifle, but trifles make perfection.” Gibbs and Devda 2 used frictional devices to record mandibular movements. They never had any jaw movement recordings of the rotating condyles moving outward and forward in their sample of 50 recordings. Either the border movements are not obtained or more probably the friction in the recording device did not allow free movement of the recording bur drilling through plastic. In order to be a relational likeness of the jaw movements and positions, the instrument must also be a mechanical likeness. The movements of the mandible are three dimensional in character and incorporate in them a sequence of movement in one plane in proportionate movement in other planes. We should not be interested in shortcuts or quick, simple, and easy money making schemes to fool the poor patient who knows nothing of the intricacies and problems of the oral mechanism. We should be interested only in how well the patient is treated.