Accuracy of a predetermined transverse horizontal mandibular axis point

Abstract

Statement of Problem. The transverse horizontal mandibular axis point may be located most precisely by a kinematic process. However, an anatomical method of locating the axis is also an acceptable technique, and an easily determined point that is consistently close to the kinematic axis would simplify transfer of the arc of rotation from the patient to the articulator. Purpose. This in vivo study compared the location of an anatomically predetermined hinge axis point with the determined kinematic axis. Material and Methods. Forty subjects (27 males, 13 females; 23 to 47 years of age) with functionally acceptable occlusion and no detectable clinical signs of temporomandibular disorders participated in the study. The earpiece alignment flags on a mechanical SAM Axiograph III combination flag/face-bow were used to locate the right and left predetermined hinge axis points, 10 mm anterior to the earpiece. The right and left kinematic center of rotation was located as described by Lauritzen and confirmed with the PC Axiotron electronic Axiograph to within 0.25 mm. All points were transferred to 1 mm2 grid paper on the subject's skin. The distance between each predetermined and kinematic point was measured ±0.25 mm. Wilcoxon and Mann-Whitney tests were used to examine differences between the left and right axis points and potential significant differences between genders at a significance level of P<.05. The number of occurrences and the distance of the predetermined axis points from the kinematic axis also were described. Results. The mean distance between points was 1.1 mm on the right (range 0.0 to 3.0 mm), 1.2 mm on the left (range 0.0 to 3.0 mm), and 1.1 mm for all 80 points (±0.63). More than 96% of the predetermined points were within 2 mm of the kinematic axis, and 67% were within 1 mm. There was no significant difference between the right and left points and no significant differences based on gender. Conclusion. Within the limitations of this study, the results suggest that the predetermined axis point is well within the clinical norm for estimated location of the transverse horizontal mandibular axis. (J Prosthet Dent 2002;87:387-94.)