Terminal hinge axis - Hobo point - Frankfurt horizontal relations

Aim of this investigation was to determine the spatial relations of the ter minal hinge axis of the temporomandibular joints toward Frankfurt horizonta l. The sample consisted of 50 examinees. Terminal hinge axis was located us ing Lauritzen's technique, on the left side efface for each examinee. Arbit rary point, as proposed by Sumiya Hobo, was measured and point Orbital was defined by palpation. On designated points steel pellets 0.25 mm in diamete r were stocked. Lathero - latheral cephalogram was obtained for each examin ee. Cephalograms were traced down on a transparent foil and points Orbital, THA - terminal hinge axis, Hobo and Porion. - as the uppermost point of th e metal ear rod of the cephalostat, were designated. Connecting points Orbi tal and Porion, Frankfurt horizontal was defined, and shortest distance tow ard points THA and Hobo, as well as between them were measured. Lines paral lel and perpendicular to Frankfurt horizontal were drawn through point THA. In a co-ordinate system defined in such a way, upper left quadrant was fir st, upper right second, lower right third, and lower left was fourth. Obser vation was made in which quadrant Hobo point was located. Measured values w ere statistically evaluated. Results revealed that Hobo point is located in first quadrant in 5 cases, in second in 7, third quadrant in 18, and in fo urth in 20 cases. That means that Hobo point is located lower to the THA po int in majority of our population. Points THA and Hobo were not identical i n any case. Mean values of variables showed that investigated points were i nferior to the FH. Measures of variability revealed great variability of bo th points toward FH, as well as for their mutual distance. It could be poin ted out that THA point should be defined kinematically during prosthodontic procedures, and that orientation in articulator's space should not be acco rding to the FH.