Methods:The subjects were 20 healthy dentate volunteers and 24 complete denture wearers.
A study was made on the stability of the [n] position and the effect that the two phonation starting positions may have on this stability: the physiologic rest position [PRP] and the intercuspal position [ICP]. The vertical interocclusal distances (IOD) during continuous [n] phonation were measured at 4 points using kinesiograph: 1 sec.,2 sec.,3 sec. and 4 sec after the start of phonation, respectively. The average value at these 4 points was calculated as the IOD at the [n] position. The IOD at the PRP was also measured.
Results:1. In 20 dentate subjects, the [n] position was very close to the ICP in both cases of started from the PRP and the ICP (from the PRP : 0.4±0.3 mm, from the ICP: 0.2±0.4 mm), and was more stable statistically than the PRP (p<0.05). 2. In 24 complete denture wearers, the [n] position started from the ICP was very close to the ICP (0.1±0.2 mm), and was more stable statistically than the PRP (p<0.05). The [n] position started from PRP could be divided into 2 typical groups : in group A(14 subjects), the [n] position was closer to the ICP(0.5±0.4 mm), and in group B(10 subjects), it was closer to the PRP(3.3±2.0 mm). The freeway space of group B(3.3±1.8 mm) was larger than that of group A(2.0±0.8 mm) , but not significantly.
Conclusion:These results suggest that the [n] position is valuable in determining the occlusal vertical dimension although it could also be affected by the starting position and the freeway space.