Human Tooth Movement Velocity is Related to Stress Magnitude and GCF Cytokines

The stress applied and inflammatory cytokines are thought to be important to tooth movement. Objectives: To test the hypotheses that 1) stresses of low magnitude do not produce a lag phase in tooth movement, and 2) tooth movement velocity is related to stress magnitude and the amounts of inflammatory cytokines in gingival crevicular fluid (GCF). Methods: Eight human subjects participated in the 84 day study. Sixteen maxillary canine teeth received a continuous retraction mechanism that produced stresses of 13, 26, or 52 kPa. Three-dimensional tooth movement was measured using a three-axis measuring microscope and a series of dental casts made at 1 to 14 day intervals. Interleukin-1b (IL-1b) and interleukin-1 receptor antagonist (IL-1RA) in GCF from experimental and control teeth were compared using an "Activity Index" (AI) = Experimental (IL-1b/IL1-RA)/Control (IL-1b/IL-1RA). Results: Analysis of covariance showed a linear relationship between stress and amount of tooth movement in 84 days (p = 0.013). A lag phase was demonstrated only by canines moved using 52 kPa. For these teeth, the AI measured in the post-lag phase was nearly twice that measured in the lag phase (p = 0.005), and average tooth movement velocity in the post-lag phase was about twice that of the teeth moved by lower stresses. Over 60% of inter-individual differences in velocity were related to AI (p < 0.001). Conclusions: Teeth subjected to stresses < 52 kPa showed no lag-phase in tooth movement. Intra- and inter-individual differences in velocities of tooth movement were related to the stress magnitude and ratio of IL-1b and IL-1RA in GCF. Funding for this project was provided, in part, by the AAOF.