Abstract: Objective To observe the three-dimensional(3D)changes of the dentition between sliding straight wire technique and double keyhole loops with heat-induced Typodont system and scanner, and to explore the effects of loading forces on the dentition under the same methodology. Methods Brackets were bonded onto a standard Typodont maxillary model, with the first premolar extracted. The sliding technique group was divided into two subgroups: straight arch group and cruve arch group. The double keyhole group was also divided into two subgroups: tip-forward group and tip-back group. The initial and post-experiment digital models were overlapped, and 3D changes were analyzed using crown marker points. Results (1)Sagittal Changes: in the straight arch group, at 250 g force value, there was significant difference in U1 between the curve arch group and tip-forward group, and in U3 and U7 between tip-back group(P<0.05). At 300 g force value, only U7 in the curve arch group and U1-U6 in the tip-back group had statistical differences(P<0.05). When the force was increased, there was no significant increase in the anterior teeth retrusion, and the advancement of posterior teeth increased accordingly in all groups. However, there were no significant differences between posterior tooth changes, except for U6 in the curve arch group and U7 in the tip-back group(P<0.05). (2)Crown inclination lip(cheek)tongue degree: the amount of anterior lingual displacement in the straight arch group was more significant than that in the curve arch group. Crown lingual displacement increased in both groups with increasing force. Under two force values, only the tip-forward group's anterior teeth showed lip inclination displacement. The tip-back group anterior teeth were close to overall movement at 250 g. Under 250 g at the posterior tooth region, only the curve arch group shifted to the inclination of crown tongue, while the remaining three groups showed buccal displacement. Under 300 g, U5 and U6 in the sliding technique group showed crown tongue inclination, and U7 tooth showed crown buccal inclination. All posterior teeth in the double keyhole group showed buccal inclination. (3)Vertical changes: at 250 g, the straight arch group elongated all anterior and posterior teeth except U7. At 300 g, the posterior tooth elongation significantly increased(U6, U7: P<0.05). At 250 g, the curve arch group achieved a certain degree of intrusion in anterior and posterior teeth. At 300 g, anterior teeth showed elongation, and posterior teeth intrusion decreased. The tip-forward group significantly lowered the anterior teeth and slightly elongated the posterior teeth. When the force was increased, the anterior tooth intrusion reduced, while posterior tooth elongation increased significantly(P<0.05). The tip-back group exhibited significant posterior tooth intrusion and minor anterior tooth extrusion. The changes in anterior and posterior teeth were not statistically significant with increasing force(P>0.05). Conclusion (1)The sliding technique group using the rocking chair reduces the degree of anterior tooth tongue inclination, posterior tooth advancement and elongation to some extent. The double keyhole group with a preset backward inclination provides relatively firm posterior tooth anchorage, while the preset forward inclination provides relatively firm anterior tooth anchorage. The double keyhole group effectively controls anterior and posterior teeth independently and prevents anterior crown tongue inclination during adduction due to front and back tilts. (2) Using larger forces does not lead to an increase in anterior tooth retrusion, but it adversely affects posterior tooth anchorage and anterior tooth torque.

Key words: Typodont, Closing gap stage, Sliding straight wire technique, Double keyhole loops, Three-dimensional changes