Immunohistochemical Analysis Of Root Resorption By Repetitive Orthodontic Force

Objectives: Repeptive orthodontic force is one of the risk factors of root resorption, and many investigators have reported that osteoclasts and odontoclasts in root resorption areas are critically regulated by RANKL and M-CSF. However, there is little information in the literature about the influence of repetitive orthodontic force on root resorption in experimental animal models. The purpose of this study was to investigate the longitudinal change of root resorption by repetitive orthodontic force immunohistochemically. Methods: Fifty-six 12-week-old male Wistar rats were used. The upper first molars were moved alternately to the buccal or lingual directions in 28 rats in the experimental group using an experimental appliance to produce repetitive orthodontic forces of 10g. In other 28 rats in a control group, the upper first molars were moved in only the buccal direction with a force of 10g using same appliance activated once a week. After 1, 3, 7,10,14,17 and 21 days, the animals were scarified. Then, the maxillae were resected and subjected to immunohistochemical analyses. The resorption area was quantified morphohistologically, and the number of TRAP-positive cells on the root surface was counted. The expression of RANKL and M-CSF was also examined by immunohistochemical staining.

Results: The amount of root resorption and the number of TRAP-positive cells were significantly greater in rats with repetitive orthodontic force than in the controls and increased time-dependently. The expression of RANKL was detected in resorption lacunae, odontoclasts, osteoclasts and stromal cells, also M-CSF was detected in odontoclasts, osteoclasts, and stromal cells in the experimental group.

Conclusions: It is shown that repetitive orthodontic force is one of the critical factors for severe root resorption. The cellular mechanism of orthodontic root resorption has a high association with the biologic activities of RANKL and M-CSF.