Administration of osteocalcin accelerates orthodontic tooth movement induced by a closed coil spring in rats

The effect of local administration of osteocalcin (OC) on experimental toot h movement was examined in the rat. The maxillary first molar was first mov ed mesially with an initial tipping force of 30 g with a closed-coil spring anchored to the incisor for 10 days (n = 48). Three experimental groups (n = 8) were injected with purified rat OC at doses of 0.1, 1, and 10 mug, re spectively. The injection into the palatal bifurcation site of the first mo lar was repeated daily. The control groups (n = 8) were injected with rat s erum albumin (10 tg), phosphate buffered saline (PBS), or were not injected . Tooth movement was evaluated daily by measuring the inter-cuspal distance between the first and the second molars on a precise plaster model. The cumulative tooth movement (mm) in the 1-mug OC-injected groups was sign ificantly more than that in all of the control groups on day 9. The rate of tooth movement (mm/day) showed periodical elevation, with high values on d ays 1, 4, 7, and 9. Acceleration of tooth movement by OC was significant in the early experimental period. Subsequently, acceleration of early tooth m ovement by OC was histologically evaluated (n = 40). Each of four animals f rom the control (PBS, n = 20) and the experimental (1 mug OC, n = 20) group s was killed daily up to 5 days. A significantly larger number of osteoclas ts accumulated on the mesial alveolar bone surface in the 1-mug OC-injected group on day 3 than that observed in control group. These results suggest that administration of OC accelerates orthodontic tooth movement due to enh ancement of osteoclastogenesis on the pressure side, primarily in the early experimental period.