Mandibular reference position: chin-point guided closure vs. final deglutition

The study investigated two mandibular positions based upon computerized axiography recordings of hinge axis movements of 262 subjects. Next to the well-known guided closure position RP (reference position by chin-point guidance), the position of final deglutition (FD) was quantified. FD represented the hinge axis position at the end of the swallowing movement. The results elicited average linear distances of 0.32 +/- 0.43 mm on the right and 0.33 +/- 0.40 mm on the left side between both positions in the sagittal plane. The average distance in the frontal plane was 0.02 mm (right) and 0.04 mm (left). Approximately 46 per cent of FD recordings were found anterior and inferior to RP, and showed significant difference to posterior and anterior-superior FD recordings. The replicability of both positions was tested on 53 subjects and averaged 0.04 mm (FD) and 0.09 mm (RP). Average deviations of repeated recordings within the subject ranged from 0.07 to 0.47 mm (FD) and 0.07 to 0.57 mm (RP) for each spatial direction. The results of this study showed a relative coincidence of an average FD and RP Variation of FD in anterior inferior direction questioned the clinical reliability of FD to reassure the guided closure position.