Methods: Ten subjects (4 men - 6 women, ages 25 to 47) at the University of Texas Health Science Center at San Antonio were selected to evaluate this relationship. An arbitrary hinge axis location described by Denar(D) was used. The true hinge axis was established using mandibular clutches fixed to the patients with Aquaseal (polyvinylsiloxane impression material). A (D) kinematic facebow was attached to the mandibular clutch and the patient’s mandible was guided into a centric relation position. In this centric relation position the patient was instructed to open less than one half inch. The (D) kinematic facebow was adjusted until the exact location of the true hinge axis was established. The distance between the arbitrary and true hinge axis was measured using a digital caliper.
Results: No statistical significant difference p less than 0.05 using paired t-test was observed between the arbitrary hinge axis and the true hinge axis. The means for the right and left arbitrary hinge axis was 13.00 mm and 13.00mm. The means for the right and left true hinge axis was 2.14 mm and 1.76 mm and the range of the right hinge axis was 0.49mm to 4.69mm and the left hinge axis 1.46mm to 3.42mm.
Conclusions: Although there are similarities between the arbitrary hinge axis and the true hinge axis, there was still a difference between these locations. This study showed the mean distance from the arbitrary hinge axis to the true hinge axis was much less than the 5 mm currently accepted difference for use of the arbitrary facebow; and that all(100%) of the true hinge axis findings were less than this 5mm accepted difference.