Abstract: Objective: To provide the reference standard of suitable force for clinics through measuring the distance of maxillary canine movement under different durations and different forces. Methods: Thirty-two cases under the growth and development period were divided into 4 groups. Different orthodontic distal forces (50g, 100g, 150g and 200g) were pressured on the maxillary canine of right side in different groups. No force was pressured on the maxillary canine of left side. The moving distances of the whole canines were measured during different time periods. Results: The movement speeds of maxillary canine were significantly different during different time periods (P<0.01). The movement speeds were also significantly different under different forces (P<0.01). Interaction was present between force and time. Conclusion: The movement speeds of maxillary canine increased following the increased forces when the force was less than 100g. However, the movement speeds did not increase dramatically when the force was more than 100g.

Key words: Orthodontics , Tooth movement , Speed, Force magnitude