The 3D Finite Element Analysis Of The Effect Of Gingival-Margin Design Of Clear Aligners On The Force Of Lower Anterior Teeth In Adult Patients With Periodontitis

Objective: To investigate the effect of gingival-margin length design of clear aligners on the lower anterior teeth with alveolar bone was absorbed to varying degrees,it provided a clinical reference for the design of aligners margin when used in adult patients with periodontitis.Methods: The 3D finite element models of clear aligners,lower dentition,periodontal ligament and alveolar bone were established.The models were divided into four groups according to the alveolar bone loss: A(normal alveolar bone height,),B(1.0mm less than normal height),C(2.0mm less than normal height),D(3.0mm less than normal height).Then each group wear four different gingival-margin clear aligners : aligner 1(scalloped cut at CEJ)、aligner 2(straight cut 1.0mm above the CEJ)、aligner 3((straight cut 1.5mm above the CEJ)、aligner 4((straight cut 2.0mm above the CEJ),for total of sixteen models.The stress distribution,displacement trend and dislocation force of lower anterior teeth were analyzed when intrusion 0.25 mm displacement was applied.Results: 1、Under intrusion loading,the stress distribution on the periodontal ligament of lower anterior teeth was approximately same in each groups,the height-stress concentrated in the tooth neck and apical region.As the degree of alveolar bone was absorbed increasingly,the stress of the periodontal ligament was gradually increased.As the margin of the aligners was shortened increasingly,the stress of the apical region decreases slightly,but the stress around the labial and lingual region increases.2、Under intrusion loading,the lower anterior teeth showed the displacement tendency of labial depression in each groups.As the degree of alveolar bone was absorbed increasingly,the displacement of the lower anterior teeth in three-dimensional was increased,As the margin of the aligners was shortened increasingly,the labial and lingual displacement of the lower anterior teeth was increasesd,and the trend of labial tipping became more obviously3、The margin of the aligners was shortened by 1.0mm,the average dislocation force of the lower anterior teeth was reduced about 11.17 ~ 21.01%;The margin of the aligners was shortened by 1.5mm,the average dislocation force of the lower anterior teeth was reduced about 20.40 ~ 34.71%;The margin of the aligners was shortened by 2.0mm,the average dislocation force of the lower anterior teeth was reduced about 27.42 ~ 45.90%.Conclusion: 1 、 Under intrusion loading,the stress distribution on the periodontal ligament of lower anterior teeth was concentrated in the tooth neck and apical region.as the degree of alveolar bone was absorbed increasingly,the stress of the periodontal ligament was significantly increased,and the dislocation force of the lower anterior teeth also increased to varying degrees.2、 When the clear aligners margin was shortened,we should strengthen the torque control of the lower anterior teeth.3、The shortened margin of the clear aligners had little effect on reducing the lower anterior teeth intrusion,and had significantly effect on reducing the stress of the periodontal ligament and the dislocation force of the lower anterior teeth.