Evaluating occlusion using centric relation records at different vertical dimensions

Objectives:  The objective of this study was to evaluate the accuracy of occlusal mountings using centric relation records at different vertical dimensions using an arbitrary facebow and a kinematic facebow.

Methods: Five prosthdontists evaluators determined occlusal differences for two patients at the University of Texas Health Science Center.  Patients had alginate impressions made that were poured in Microstone.  On each patient a true hinge axis was established using a Denar(D) kinematic facebow.   A Whipmix(W) arbitrary earbow  was also used on each patient to transfer this relationship to an (W) articulator.  Centric relation was established for each patient using a leaf gauge at 3.00mm and 1.50mm. Five evaluators  determined the occlusal differences for each patient on the two different articulators.  The evaluators were asked to rate the discrepancies between the kinematic facebow and the arbitrary facebow from the two different records.  The rating was no difference, slight difference, and major difference.

Results: There was no statistical difference with ≥ 0.05 using Chi squared in the prosthodontists evaluations between the arbitrary facebow and the kinematic facebow at the two different relationships; however there was a significant difference ≤ 0.05 between the 3.00mm record and the 1.50mm record with the kinematic facebow.  The records for the arbitrary facebow and kinematic facebow are:  0,0 no difference, 5,0 slight difference, and  5,10 major difference for the 3.00mm record and 0,0 no difference, 5,5 slight difference, and 5,5 major difference for the 1.50mm.

Conclusions: The resulting occlusion when using a kinematic facebow after changing vertical dimension does not appear to be completely accurate.  Changing vertical dimension when using both the kinematic and an arbitrary facebow showed major differences in occlusion.  The study suggests that when changing vertical dimension a new centric relation record should be made at that vertical dimension.