The hinge axis concept: a radiographic study of its relevance.

The "hinge axis concept" maintains that the mandible moves around a transverse horizontal axis through both condyles. Since it was introduced in the 1920s it has had a profound impact on clinical dental practices all over the world. By use of the radiographic subtraction technique, we demonstrated that an increase in the occlusal vertical dimension of 4 to 7 mm in the retruded position resulted in a small positional change (range 0.31 to 1.84 mm) in an unpredictable direction. Pure rotation did not occur; however, the condylar displacement is probably of minor clinical importance in prosthodontic restoration.