Evaluating The Effect Of Double Keyhole Loops Torquing Anteriors With Alveolar Bone Loss—A FEM Study

Aim1.Setting up 3D finite element models of upper anteriors with alveolar bone loss during en-mass retraction with double keyhole loops.2.Through deforming wire of canine segment with continuous ligation on loop tops,explore effect of anterior torque control under different degrees of deformation.Analyze this force system's effect on anterior periodontal ligament with different degrees of alveolar bone loss.Methods1.Select an volunteer with healthy periodontal condition.We use CBCT scanning to collect data of maxilla,upper arch and other dentition data,utilize softwares to adjust treshold in order to establish initial 3D models.We use Geomagic Studio to set up properties of different tissue and gain 3D finite element models of upper anteriors with different degrees of alveolar bone loss by decreasing alveolar bone by 0mm,1mm,2mm,3mm.2.Open the distal loop by loading distal force with ligature.Continuously ligate mesial and distal loops till anterior wire plane is at 1°,3°,5°,7° angle to horizontal plane.Analyze trend of anteriors' relative movement and periodontal ligament's strain change by applying 3D finite element analysis on stimulation of upper en-mass anterior retraction.In this research,we load wire force on models of maxilla and dentition with 0mm,1mm,2mm,3mm alveolar bone loss.Results3.3D finite models of the maxilla,upper arches,and double keyhole loops in this research present high precision and fine geometric similarity.4.Anterior teeth with load of double keyhole loops all tip.Canines tip the most.5.The more we load force on mesial and distal of the loops,trend of anteri-or lingual crown torque in each condition and anterior vertical extrusion relatively decrease.6.Under the condition with no bone absorption,lateral incisors intrude as do-uble key hole loops deform.Under other conditions,lateral incisors all extrude.7.Canines rotate while retracting with double keyhole loops.In 3D dimensio-ns,canines displace the most.8.As alveolar bone decreases,trend of anterior crown and root movement re-latively increase.Trend of anterior extrusion and lingual root torque increase.Wh-en bone resorption goes under 1mm,equivalent strain on canine periodontal ligament reaches 3.01E-02 MPa.When bone resorption goes under 3mm,equivalent str-ain on lateral incisor periodontal ligament reaches 3.41E-02 MPa.They all surpass physiological limit of periodontal ligament.Conclusion1.As continuous labial arch,double keyhole loops have effect on each tooth.2.Double key hole loops control anterior better than canines3.As alveolar bone decreases,anterior crowns with same load and tendency of root movement tendency,anterior extrusion and lingual root torque movement all increase.Periodontal loss may further aggravate when alveolar bone level reaches a certain degree and force on periodontal ligament surpasses biological limit.