ABSTRACT
Objective To study the influence of different moment-to-force ratios (M/F) and forces on canine displacement and periodontal ligament (PDL) stress. Methods A three-dimensional (3D) mandibular model was established based on CT images. The orthodontic force systems without a moment and with various M/F were applied to the canine for numerical calculation of its translation. An optimum force system to realize canine translation was validated by analyzing translation displacement of the canine in each case. Results The PDL stress increased with an increase in force magnitude in all cases. The PDL stress first decreased with an increase in the M/F before the M/F reached the optimum value (M/F=10.1 mm), and then increased with an increase in the M/F. The initial displacement of the canine was inclined movement, which was most close to translation when the precise optimum M/F was applied. Conclusions The canine movement requires an appropriate force to prevent root absorption, whereas the translation movement requires an optimal M/F value which is within the physiological range. Understanding the influence of force and moment on tooth translation can help to apply more reasonable orthodontic force system and design more reasonable orthodontic device.