An experimental evaluation of effects and side effects of asymmetric face-bows in the light of in vivo measurements of initial tooth movements.

By using a magnetic sensing system, the translational and rotational molar movements under the application of various asymmetric face-bows were measured two-dimensionally in human subjects to evaluate their primary effects and side effects. The asymmetric face-bow designs tested were three types of power arm face-bows, swivel offset face-bow, and internal hinge face-bow. Although all face-bow designs were considered to be effective in achieving asymmetric distalizations of the molars, they generated lateral displacements that may lead to an undesirable crossbite. The swivel offset face-bow may produce unexpected results and its fabrication is complicated. The internal hinge face-bow is remarkably effective for asymmetric molar distalizations. Unfortunately, it causes a strong crossbite tendency on the molar to be more distalized. Therefore the use of the power arm face-bow is thought to be relatively recommendable because it showed an acceptable asymmetric effect and is easily fabricated from a commercially available face-bow. It is concluded that all asymmetric face-bows generate lateral forces as side effects as long as the force delivery system with a combination of an asymmetric face-bow and a neck strap or head cap is applied. The current study suggests a method whereby the side effect of asymmetric face-bows can be eliminated.