Aim: To observe pain-related behavior response to experimental tooth movement by different orthodontic forces. Methods: A total of 78 8-week-old male SD rats weighted( 266. 67 ± 20. 46) g were randomly allocated into control group and experimental group. The experimental group received a directed orthodontic force to the upper left molars at different magnitudes of force( 50 or 100 g). The pain-related behavior was evaluated on the first,second,third,fifth,seventh,fourteenth day. Results: There were signifi...