High-resolution observations of human premolar eruption.

Using an optical instrument based on the principle of Moire magnification to obtain resolution of less than 0.1 mu m, eruption of maxillary second premolars was observed during the prefunctional phase of eruption in 10 children. The participants were observed on four occasions for approx. 30 min each, once in the afternoon and once in the evening on two consecutive days. For all participants, a pulsatile movement of the erupting tooth was noted in concert with the arterial pulse. Significant variations in short-term eruption rates and patterns were observed, with a mean rate of 0.28 mu m/min over continuous 20-min periods but a range from -0.91 to 2.29 mu m/min. During most sessions net eruption occurred, but in several of the 30-min periods there was little movement or intrusion. An unexplained cyclic phenomenon was observed consistently, which had a period of 20-50 s and a range of magnitudes from 0.12 to 2.22 mu m. It seems clear that a discontinuous pattern of eruption occurs in short-term as well as longer-term observations.