OBJECTIVEThis study aims to investigate the temporal pattern of expression of vascular endothelial growth factor (VEGF) and new bone formation during midpalatal suture expansion osteogenesis for rapid maxillary expansion.

METHODSA total of44 New Zealand white rabbits were randomly assigned to 11 groups, namely, five experimental groups, five control groups, and one control 0 group. A Haas appliance was used for the rapid expansion of the midpalatal suture; rapid expansion was set for 2 weeks and fixed for 4 weeks. The tissue of the maxillary midpalatal suture was harvested on the day of installing rapid expansion (control 0 group), on weeks 1 and 2 for rapid expansion, and on weeks 1, 2, and 4 for fixed (experimental group and control group, respectively). The immunohistochemical method was used to detect distribution and expression of VEGF, and new bone formation was observed with periodic acid-Schiff.

RESULTSHigher VEGF expressions are observed after midpalatal suture distraction osteogenesis. Positive staining for VEGF is mainly noted in the vascular endothelial cells, and the active osteoblasts are at the edge of a newborn trabecular bone. A weak VEGF expression is detected among cells in the control group. The VEGF expression of the experimental group is higher than that of the control group in rapid expansion weeks 1 and 2 and in fixed weeks 1 and 2. The expression of VEGF in the experimental group increases significantly and peaks at fixed week 1, and then gradually decreases. The amount of newly formed bone in the experimental groups is always higher than that in the control group; moreover, it increases significantly and peaks at fixed week 2, and then gradually decreases.

CONCLUSIONThe mechanical strain created by rapid maxillary expansion generates a sequence of VEGF cellular events that lead to increased vascularization and subsequent new bone formation.