Investigation into the behavior of symmetrically and asymmetrically activated face-bows

The distal and lateral forces and also the couples (in a transverse plane) delivered by the inner terminals of a face-bow have been derived analytically according to the complementary (strain) energy method for various face-bow configurations on the assumption that the terminals are rigidly held by the molar tubes and that the external forces acting are in the plane of the inner bow. The results of the theory have been checked experimentally with a specially designed apparatus in which two mild steel transducer pegs that carry three pairs of strain gauges were used to measure the force system delivered by the inner bow under a range of loading, both symmetrical and asymmetrical. Good agreement with the theory was obtained, confirming the validity of the theoretical analysis. It is concluded that force systems are dependent on bow geometry and that with increasing asymmetry of the external loading transference of the distal load to the power-arm side is accompanied by a shift of lateral force and couple to the opposite side.