Errors in mounting maxillary casts using face-bow records as a result of an anatomical variation

Abstract

The relationship of the teeth to the intercondylar axis and horizontal plane is transferred to the articulator by means of a face-bow record. In most semi-adjustable articulators, the horizontal plane to which the maxillary cast is orientated is the Frankfort plane or its near equivalent, the orbital-axis plane. For this purpose the infraorbital notch is used as the anterior reference point Clinical observations of Cantonese patients suggest that in some individuals the Frankfort plane may not be horizontal, with the result that the orientation of the casts in the articulator is incorrect with respect to the horizontal plane, and a preliminary study has been undertaken to investigate this range of variation. Lateral cephalometric radiographs were taken of 33 Cantonese male adult subjects in natural head posture. The cephalometric landmarks of the Frankfort plane were recorded relative to the true vertical axis and, by the use of a digitizer, fed into a computer for analysis. The results show that there is considerable individual variation in the orientation of the Frankfort plane. Variations ranging between +11° and -2° in relation to the horizontal were recorded. Large anatomical variations may make errors difficult to avoid when the manufacturers' recommended anterior reference point for a particular face-bow is the infraorbital notch. Clearly this is a source of potential error which should be recognized when treating this ethnic group. © 1985.