Estimated and true hinge axis: a comparison of condylar displacements.

The purposes of the investigation were: i) to compare the condylar displacements from centric slides for 74 sets of casts mounted with an estimated versus a true hinge axis; ii) to determine the error in hinge axes location on the recording of condylar displacements from centric slides; and iii) to define the reproducibility of the Mandibular Position Indicator (MPI), a method of measuring condylar (in vitro) displacements from centric relation position. The findings revealed that routine use of the true hinge axis to obtain MPI readings for analysis of diagnostic casts is not warranted. The mean standard error of MPI double readings attributed to both hinge axes location was 0.4 mm for each component in the sagittal plane. Of the 0.4 mm of mean standard error, 0.2 mm was contributed by the lack of reproducibility of the MPI. The centric relation bite registration technique outlined in this study always captured a superior articulator position of the condylar mechanism. The condylar distractions and deflections from centric relation to maximum intercuspation were primarily in an inferior direction with a smaller posterior component.