Applying Typodont To Compare The Dentition Changes In Closing Space Of Extractions Between Sliding Straight Wire Technique And Double Keyhole Loops

ObjectiveWe used the Heated-induced Typodont system and scanner to obtain the digital model.This study aimed to compare the 3D changes of the dentition between sliding straight wire technique and double key loops,and to explore further the effects of loading forces on the dentition under the same method.MethodsWe bonded brackets on the standard Typodont maxillary model without the extracted first premolar.The model alveolar part was made of sticky wax;the dental arch was made of resin crowns and metallic root teeth;the pars palatalis with three protrusions was cast by gypsum.The Studyal group A used a sliding straight wire technique to close extraction space,and was divided into two subgroups:group A1 without and group A2 with a rocking chair,respectively.Group B used double key loops technique,and was divided into two subgroups:group B1 loaded 30 degrees tip-forward bend on the anterior teeth,and group B2 loaded 30 degrees tip-back bend on the posterior teeth.In addition,250g and 300g forces were applied for both techniques.Corresponding force values were loaded with the traction hook and elastic chain in group A,with traction hook and ligated wire in group B.We overlapped the initial and the post-experiment digital models,and analyzed the displacement of the crown landmarks.According to the normal distribution test of the dataset,paired T-test or Wilcoxon signed rank analysis was performed.Result:1.In sagittal,for all the study groups,anterior teeth showed retrusion,and posterior teeth moved forward.Group A1 compared with group A2,B1,B2.At 250g force values,only group A2 U1,group B1 U1 and group B2 U3,U7 had statistical differences(P<0.05).At the 300g force value,only group A2 U7 and group B2 U1-U6 had statistical differences(P<0.05).Increasing force,there was no significant increase in the anterior teeth retrusion,and the advancement of posterior teeth increased accordingly in study groups.But except for the group A2 U6 and group B2 U7,there were no significant differences between posterior tooth changes(P<0.05).2.In the inclination of crown lip(cheek)tongue degree,the amount of anterior lingual displacement in A1 group was greater than A2,and at 250g,50%of comparison was statistically(P<0.05).With increasing force,the amount of crown lingual displacement increased in both two groups,but except for the edge point of U2 the difference was not significant(P<0.05).In all groups,only the B1 group anterior teeth showed lip inclination displacement.The B2 group anterior teeth were close to overall movement at 250g.With force increasing,the anterior in group B1 labial tilt decreased but had no statistically significant difference.While in the B2 group,U1 crown mild tongue tilt,U2,U3 can still achieve the overall movement,only the edge point of U2 was statistically significant(P<0.02).At 250g,only group A2 the posterior tooth region shifted to the inclination of crown tongue.The remaining three groups showed buccal shift towards displacement in the posterior teeth.At 3 00g,except for U5 and U6 in group A showed crown tongue inclination and U7 tooth showed crown buccal inclination.All posterior teeth crown in group B showed buccal inclination.3.In vertical,at 250g,the A1 group elongated the anterior and posterior teeth except U7.At 300g,it elongated the anterior and posterior teeth,and the posterior tooth elongation increased significantly(U6,U7:P<0.02).At 250g,the A2 group could achieve a certain degree intrusion in anterior and posterior teeth.At 300g,anterior teeth showed elongation and posterior teeth intrusion decreased.There was a significant difference in all teeth’ positions except U5 and U7(P<0.05).The B1 group could significantly lower the anterior teeth,and had small posterior teeth elongation.Increasing the force value,the anterior tooth intrusion was reduced but only the U2 had significant difference(P<0.03),and posterior teeth elongation increased significantly(P<0.02).In the B2 group,the posterior teeth intruded significantly,and showed minor anterior teeth extrusion.With the force value increasing,the changes of the anterior and posterior teeth were not statistically significant.Conclusion:1.When closing the clearance,the sliding method loaded rocking chair could reduce the degree of anterior tooth tongue inclination,posterior tooth advancement and elongation to some extent.The double-key group could lower the anterior and posterior teeth respectively and prevent the anterior crown from tongue inclining during adduction by the front and back tilt.Double key curve preset backward inclination can obtain relative strong posterior tooth anchorage,and preset forward inclination can obtain relative strong anterior tooth anchorage.2.Using larger force do not show an increase in the anterior tooth retrusion,but adversely affected the posterior tooth anchorage and the anterior tooth torque.