Receptor activator of nuclear factor-kappa ligand, OPG, and IGF-I expression during orthodontically induced inflammatory root resorption in the recombinant human growth hormone-treated rats

Abstract

Objective: To investigate the effects of growth hormone (GH) on local receptor activator of nuclear factor-kappa ligand (RANKL), OPG, and IGF-I expression during orthodontically induced inflammatory root resorption in rats.

Materials and methods: Forty Wistar rats (gender: male; age: 7 weeks) were randomly divided into control and experimental groups. A force of 50 g was applied to move the right upper first molars mesially. The experimental and control groups received daily subcutaneous injections of recombinant human growth hormone (GH; 2 mg/kg) and equivalent volumes of saline, respectively. The rats were sacrificed on days 1, 3, 7, and 14. Micro-computed tomography-reconstructed images of the upper right first molars were used to survey root resorption and tooth movement. Horizontal sections of the maxillae were prepared for hematoxylin and eosin, tartrate-resistant acid phosphatase, and immunohistochemical staining.

Results: Resorption lacunae appeared on the compressed side of the distal buccal root of the right first molar on days 7 and 14. Compared with the control groups, GH-treated groups showed more RANKL-positive cells and osteoclasts on day 3 and more OPG- and IGF-I-positive cells and fewer odontoclasts on days 7 and 14. Indexes of root resorption were lower and tooth movement was faster in the GH-treated groups than in the control groups on days 7 and 14.

Conclusions: The inhibitory effect of GH on root resorption by heavy force might be mediated by RANKL/OPG and IGF-I. Short-term GH administration may be a method with which to reduce root resorption and shorten treatment time, especially in patients who are susceptible to root resorption.

Keywords: IGF-I; OPG; RANKL; Root resorption.

Figure 1.

(a) Intraoral photograph of the appliance. (b, c) H&E staining of unloaded root (b) and loaded root (c) on day 7. (magnification, 200×). D indicates dentine; PDL, periodontal ligament; and AB, alveolar bone. (d–h) Reconstructed three-dimensional micro-CT image showing root resorption and the distance of tooth movement on day 14; (d) unloaded root; (e) Loaded root; (f) No tooth movement in the appliance-free tooth; (g) Tooth movement in the control group; (h) Tooth movement in the experimental group; (i, j) Quantification of the ratio of the volume of root resorption craters (j) and tooth movement (i). * P < .05 compared with the control group. Arrow indicates root resorption lacuna.

Figure 2.

TRAP staining (magnification, 400×). On day 3, the osteoclasts (arrows) on the alveolar bone surface were more numerous in the experimental group than in the control group (d, a, g). TRAP-positive multinucleate odontoclasts (arrows) appeared on the root resorption lacunae on days 7 (b, e) and 14 (c, f), with fewer in the experimental group than in the control group (h). D indicates dentine; PDL, periodontal ligament; and AB, alveolar bone. * P < .05 and ** P < .01 compared with the control group.

Figure 3.

Immunohistochemical observations of RANKL and OPG expression in PDL cells (magnification, 400×). RANKL-positive cells (arrows) in the control (a) and GH-treated (b) rats on day 3; OPG-positive cells (arrows) in the control and GH-treated rats on days 7 (c, d) and 14 (e, f). RANKL-positive cells on day 3 (g) and OPG-positive cells on days 7 and 14 (h) were significantly increased in the experimental group. The RANKL/OPG ratio was greater in the experimental group than in the control group on day 3, but lower in the experimental group than in the control group on days 7 and 14 (i). D indicates dentine; PDL, periodontal ligament. * P < .05 and ** P < .01 compared with the control group.

Figure 4.

Immunohistochemical observations of IGF-I expression in PDL cells (magnification, 400×). IGF-I–positive cells (arrows) were significantly more numerous in the experimental group (b, d) than in the control group (a, c) on days 7 and 14 (e). D indicates dentine; PDL, periodontal ligament. * P < .05 and ** P < .01 compared with the control group.