Using Of Bracket Pre-tied Archwire For Orthodontic Extrusion Of Anterior Teeth With Root Or Crown-root Fracture

Objective: The purpose of this study is to describe an effective technique of bracket pre-tied archwire with portal loop for extrusion of subgingival or partial subgingival incisor roots,and analyze the convenience of operation,reconstruction of periodontal tissue(gingiva and alveolar bone)and the root traction angle.Methods: 15 subgingival(or partial subgingival)residual roots / crowns from 14 patients,who visited the orthodontics department of the Second Hospital of Hebei Medical University from July 2015 to October 2019,were involved in this study.The 0.019 × 0.025 in stainless steel square wire with pre-tied brackets was bending on a plaster working model including 2 to 3 normal teeth adjacent the target tooth,and then bonding the device on the teeth using light-cured resin.A lingual button was stick on the temporary crown neck of the target root for the orthodontic extrusion.The analyzation was performed for 1.The moving speed and traction time of the affected tooth before and after treatment;2.The relationship between the direction of the traction force and the root elongation;3.Whether the periodontal soft and hard tissues also migrate following the root movement;4.Whether the unnecessary movement occur on the adjacent teeth.Results: 1.The average traction time of 15 teeth was 3.6 months,the average traction speed was 0.68 mm / month(0.17 mm / week),and the average course of treatment(including the traction and retention time before removal)was 7.9 months,which all reached the expected traction effect.2.The traction of the application point in the direction of the tooth surface will cause the palatal inclination in the process of root elongation.The traction of the labial positive angle will help the root to extend substantially along the axis of the tooth.3.In the process of slowly moving the root with conventional orthodontic force,the soft and hard tissues attached to the neck of the tooth appear to go down different degrees of elongation along with the elongation of the tooth.When the reconstruction is obvious,gingival surgery is required to create the height of the gingival margin to make the morphology coordinated with adjacent teeth.4.The bracket pre-tied archwire does not cause abnormal movement of adjacent healthy teeth and is easy to remove and wear,which is conducive to periodontal inspection during treatment,bracket fall off and rebonding.Conclusion: Orthodontic light traction using bracket pre-tied archwire combined with portal loop is convenient to treat residual roots / crowns.This method can accurately control the traction distance,effectively prevent root tilting and abnormal movement of adjacent teeth,and help to stable the orthodontic result.On the other hand,low speed root elongation can sometimes lead to unnecessary positional and morphological changes of the gingival margin.