[The effects on upper first molars by the face-bow construction. Consideration of utilizing the strain gauge method and the computer method of structural analysis].

Abstract

The present study was undertaken for the purpose of detecting the influence on upper first molars by the dynamic behavior originated in face-bow construction. Tests were made at occipital pull and cervical pull face-bows utilizing strain gauge method and the computer method of structural analysis. As for the occipital pull face-bow, a short outer-bow 35 mm frontward of a tube was bent 30 degrees upward and be pulled in that direction. As for the cervical pull face-bow, a medium outer-bow flash to tube, parallel to the inner-bow was pulled from 20 degrees downward. These two types of face-bows were divided into 4 types, those with loops at the back end (WL) and to those without loops (NL). In the strain gauge method, the force and moment to tubes was measured and compared with the values obtained from theoretical analysis. And in the structural analysis, the data of deflection was compared with each other. Those results indicated that 1. face-bow shows a different force to the molars and a different phase of deflection, according to the difference of it's force concentrative section. 2. the larger the deflection, the larger the deviation of forces on molars from theoretical values. 3. the way of setting loops against the direction of pull alters the phase of deflection of face-bow and the force on molars. 4. existance of loops at inner-bow affects as follows: (1) Reduction of moment of each type of face-bow. (2) Reduction of vertical force at occipital pull face-bow and it's increase at cervical pull face-bow. (3) Resistance for deflection of face-bows in the case of tractive force for closing loops.