Long-wave cycles in the position of erupting human premolars.

OBJECTIVE: Unusual long-wave cycles in the position of an erupting human premolar were first noted by Trentini et al. [Trentini CJ, Brown WH, Paterson RL, Proffit WR. The application of Moire magnification to high precision studies of human premolar eruption. Arch Oral Biol 1995;40:623-9]. This report characterises them in detail and evaluates their significance relative to human tooth eruption. DESIGN: The magnitude and frequency of Trentini cycles were examined in high-resolution recordings of premolar eruption in patients without and with periapical infiltration of a vasoconstrictor or vasodilator, and the possibility of artifact due to the natural frequency of vibration of a tooth-PDL system or to building vibration was evaluated. RESULTS: The cycles are characterised by a magnitude of 1.3 +/- 0.5 microm and a frequency of 1.8 +/- 0.5 cycles per minute, with greater variation between than among subjects. They cannot be explained as a natural frequency phenomenon, and vibration from microseism is highly unlikely. The cycles disappear when blood flow to the periapical area of the tooth is interrupted and reappear when blood flow resumes. CONCLUSIONS: The cycles appear to reflect a physiologic rhythm, probably related to blood flow in the periodontal ligament. Because they are similar whether or not a tooth is erupting at a particular time, however, it appears that they are not a direct reflection of a blood flow-related eruption mechanism.

Response of erupting human second premolars to blood flow changes.

The effect of infiltration of a vasodilator and a vasoconstrictor [2% lidocaine (lignocaine) without or with 1:100,000 adrenaline (epinephrine)] above the root apex of human second premolars in the prefunctional stage of post-emergent eruption was evaluated for 11 teeth in eight children. On two consecutive days, 30 min of high-resolution data on changes in tooth position were collected for each participant during each of four sessions, two in the afternoon and two in the evening, using an optical instrument based on Moiré magnification with 0.05 microm resolution. The immediate reaction to the 1.8 ml injection was extrusion of the tooth, which lasted 2-4 min. After that, in the majority of teeth receiving a vasodilator, the reaction was an increased rate of eruption. In teeth receiving a vasoconstrictor, a decrease in eruption or intrusion was noted after the initial extrusion. The low-frequency Trentini cycles characteristic of erupting teeth were immediately obliterated in all teeth receiving injections. In the next few minutes, the cycles reappeared in teeth receiving the vasodilator, but did not reappear or reappeared only partially in teeth receiving the vasoconstrictor. It appears that vascular changes can influence the rate of prefunctional post-emergent eruption.