[Study on the horizontal reference plane in prosthodontics. Establishment of the anterior reference point]

This study was made to obtain the anterior reference point for determining the horizontal reference plane in prosthodontics for transferring the model in the natural head position of each patient onto the articulator in dental clinics. The results thus obtained are as follows: 1. Measuring points in the sitting and standing postures were located below the orbital point, respectively. 2. The natural head position tended to shift upward significantly more frequently in the standing posture than in the sitting posture. 3. The natural head position in the standing posture varied less and was more restorable than in the sitting posture. 4. The natural head position in the mirror-viewing method varied less and was more restorable than in two other methods. 5. Between the three reference points in the natural head position, the measurements based on the orbital point and the inner canthus of the eye showed less variance than the measurements based on the ala of the nose. 6. The ratios calculated from the measurements based on the reference points in the natural head position showed slightly more variance than the measurements based on the reference points. 7. From the above, it can be said that the point 23.3mm below the inner canthus of the eye, which was the average of measurements taken with the mirror-viewing method in the standing posture, may be appropriate for use as the anterior reference point for transferring the model in the natural head position of each patient onto the articulator.