The effect of continuous intrusive force on human pulpal blood flow

The purpose of this study was to examine the effect of continuous intrusive force application on human pulpal blood flow (PBF). Recordings were made of 13 vital upper left central incisors in 13 healthy participants (experimental group, n = 8; control group, n = 5) who had clinically healthy tooth crowns and periodontal tissues. PBF was recorded by means of a laser Doppler flow meter (LDF) with an opaque rubber dam applied to the teeth. The basal blood flow in the pulp (BBFP) was compared during three observation periods: (1) before orthodontic archwire engagement; (2) during wire engagement (control group: no application of force; experimental group: continuous intrusive force of 0.5 N); and (3) after the removal of the wire. In the experimental group, brief intrusive forces (magnitude 0.5, 1.0, and 2.0 N) were applied to the incisal edge of the examined teeth to determine their effect on acute changes in PBF. The results obtained were as follows: (1) the BBFP in the experimental group was significantly reduced during the period of continuous intrusive force application (P < 0.05), which was followed by recovery after the removal of the wire. (2) Brief intrusive force produced a significant reduction of PBF (P < 0.05), but the reduction rate (percentage) did not differ significantly during the observation periods. The results indicate that the measurement technique shown in this study could detect PBF change produced by continuous orthodontic force application.