Figure 2: Immunohistochemistry analysis of HIF-1α protein expression in rat dental pulp tissue after orthodontic force. HIF-1α protein was weakly stained in control group (a). (b–e) HIF-1α protein expression became strongly stained after 1, 3, and 7 d of orthodontic force and reached the peak level at 2 w group. Then HIF-1α protein expression weakened in the 4 w group but was still higher than the control group (f). Arrows indicate the vessel wall (images on the left: magnification ×200, bar = 100 μm; images on the right: magnification ×1000).