Human interleukin-1β and interleukin-1 receptor antagonist secretion and velocity of tooth movement

The cytokines interleukin-1β (IL-1β) and IL-1 receptor antagonist (IL-1RA) probably play a part in orthodontic tooth movement. Here, the force magnitudes and the area of force application in the compressed periodontal ligament (PDL) were controlled and the velocity of tooth movement correlated with concentrations of IL-1β and IL-1RA in the gingival crevicular fluid (GCF). Seven individuals undergoing orthodontic treatment involving maxillary first premolar extractions and distal movement (bodily retraction) of the maxillary canines participated in the 84-day study. For each participant, continuous retraction forces were applied so that they received equivalent PDL stresses of 13 kPa for one canine and 4 kPa for the other. GCF cytokine concentrations from experimental and control teeth were expressed relative to total protein in the GCF and compared using an 'Activity Index' (AI) = Experimental (IL-1β/IL-1RA)/Control (IL-1β/IL-1RA). The results showed that the velocity of tooth movement in an individual was related to their AI. The correlation between AI and tooth movement was stronger from the distal (R_d = 0.78) than from the mesial (R_m = 0.65) of retracted teeth. The results demonstrate that equivalent force systems produce individual differences in cytokine production, which correlate with interindividual differences in the velocity of canine retraction.