Raymond B. Winstanley

Comparison of the replicability of routinely used centric relation registration techniques.

PURPOSE This study was conducted to determine statistically the most repeatable mandibular position of 3 centric relation methods. MATERIALS AND METHODS Three centric relation recording methods commonly reported in the literature were selected: bimanual mandibular manipulation with a jig, chin point guidance with a jig, and Gothic arch tracing. Fourteen healthy adult volunteers (7 males and 7 females), with an average age of 26.61 +/- 4.20 years and no history of extractions, temporomandibular joint dysfunction, or orthodontic treatment, were selected for the study. Accurate casts were mounted on an articulator (Denar D4A) by means of a facebow and maximum intercuspation silicone registration record. A mechanical 3-dimensional mandibular position indicator was constructed and mounted on the articulator enabling the operator to analyze the mandibular positions in 3 spatial axes (x, anteroposterior; y, superoinferior; z, mediolateral shift). Each centric relation method was recorded four times on each subject (at baseline, 1 hour, 1 day, and 1 week at approximately the same time of day). Records were transferred to the articulator, and data were extracted using a stereomicroscope modified to accept the mandibular position indicator. RESULTS Variability within subjects ranged from 0.03 mm (left-side z axis for the bimanual method) to 1.6 mm (left-side y axis for the Gothic arch method). To indicate the least variable (most repeatable) method a comparison was made using the F test. The bimanual method was the most consistent, showing between 10.11 (p = 1) and 0.438 (p = 0.005) times less variation than the Gothic arch method (the least consistent). The repeatability of the chin point guidance method was somewhere between the other 2 methods. CONCLUSIONS The results of this study showed that of the 3 centric relation methods evaluated, the bimanual manipulation method positioned the condyles in the temporomandibular joint with a more consistent repeatability than the other 2 methods, whereas the Gothic arch was the least consistent method.

Observations on the use of the Denar pantograph and articulator.

An investigation was undertaken to determine the reproducibility of articular settings from graphic records of simulated mandibular movement using the Denar pantograph and the Denar D4-A articulator. The results of the study showed that most of the articulator adjustments were reproducible with a reasonable degree of accuracy, although not quite to the extent one would hope for. The rear-wall and top-wall adjustments are of questionable value in reproducing mandibular movements with this technique, since the results for these adjustments in the present study were unreliable. However, familiarity with the technique gave better results, as shown in the third experiment. It would, therefore, seem that much of the basis for adverse reports depended upon results obtained by operators with insufficient experience in the technique.

Graphic tracings of condylar paths and measurements of condylar angles

A study was carried out to determine the accuracy of different methods of measuring condylar inclination from graphical recordings of condylar paths. Thirty subjects made protrusive mandibular movements while condylar inclination was recorded on a graph paper card. A mandibular facebow and intraoral central bearing plate facilitated the procedure. The first method proved to be too variable to be of value in measuring condylar angles. The spline curve fitting technique was shown to be accurate, but its use clinically may prove complex. The mathematical method was more practical and overcame the variability of the tangent method. Other conclusions regarding condylar inclination are outlined.

Hinge axis location on the articulator

Experiments were undertaken to determine the accuracy of hinge axis location using clinical methods on articulator. Errors were found to occur up to an area 2.4 mm in diameter, but most of results were more accurate than this. Results were better with an opening in the anterior region of the articulator of 15 mm rather than 10 mm. It would appear that better results could be obtained using a microdot pattern flag rather than a plain record blank to determine the rotation center. The first experiment gave good results, although only one participant had any previous experience of hinge axis location, and it is debatable whether or not this experience is necessary before satisfactory results can be obtained. The only statement which can really be made from these results concerning the value of previous experience is that with a plain flag, previous experience is more helpful for an articulator opening of 10 mm but not for an opening of 15 mm. The results of these experiments are in keeping with those of other investigators.

The Gothic arch (needle point) tracing and condylar inclination

The records of 11 patients referred for treatment of TMJ disorders were used to compare condylar inclination found by drawing a tangent and by using a mathematic technique. Needle point tracing angles were also measured for the same patients and were compared with the condylar inclination. It can be concluded that (1) the mathematic technique outlined records a more accurate condylar angulation, and (2) there is a great variation in condylar inclination values between patients and between left and right sides of the same patient, and (3) there is no direct relationship between condylar inclination and the needle point tracing angle.