Abstract: Abstract: Objective To analyze the effect of different heights of the traction hook on the stress distribution on the maxillary incisors periodontal ligament and initial displacement and to discuss the mechanical mechanism in the process of J-hook traction in order to provide objective theory basis for clinical orthodontics. Methods Three-dimensional finite element models of the maxillary anterior teeth and the appliance werefirst established; the traction hook height was respectively 2,4,6,8,10 and 12 mm;a fixed angle of 30°was maintainedfrom the sagittal plane toward cheek and occlusal plane upward with 1.5 N; A seriesof stress distributionmaps and initial displacement maps were made. Results With the traction hook height increasing,the maximum principal compressive stress of central incisors became larger,and lingual inclination was down when traction hook height was less than 4 mm,while the labial inclinationwas down with hook height greater than 8 mm; the maximum principal stress of lateral incisordecreased at first and then increased,with the minimum stressvalueoccurred attraction hook height of 4 mm while the maximum stressvalueoccurred attraction hook height of 12 mm,andthe elongation tendency of lingual inclination increasedwith the height of traction hook increasing. Conclusions As towing hook height increases,the central incisors trend to lingually -down at firstand thenlabially -down; the lingual inclination elongationtendency of lateral incisor increaseswith the height of traction hook increasing.

Key words: maxillary incisors, dimensional finite element, J hooks, traction hook