Orthodontic Retention Of Lower Anterior Teeth Of Different Alveolar Bone Heights With Lingual Fixed Retainers In Different Positions:A Finite Element Analysis

Objective: This study explores the optimal placement of lingual fixed retainers in patients with alveolar bone resorption to minimize tooth movement and prevent excessive stress concentration on periodontal tissues.The aim is to maximize the preservation of orthodontic results,reduce chances of relapse,and maintain periodontal tissue health.The investigation evaluates the impact of alveolar bone height and retainer position on tooth displacement and Von Mises Stress in periodontal tissues under occlusal load,thereby providing a theoretical foundation for retention strategies in orthodontic patients with reduced alveolar bone height.Methods: A volunteer who had recently completed orthodontic treatment was selected,and CBCT image data was collected.Sixteen sets of 3D models of four different alveolar bone heights(without resorption,1/3 resorption,1/2 resorption,2/3 resorption)of the mandibular anterior region without retainer and with three different positions of mandibular lingual retainers(incisal 1/3,mesial 1/3,cervical 1/3)were created by Mimics,Geomagic Wrap and Solidworks software.The finite element model was then built with Hypermesh and Abaqus software,loaded with occlusal forces,and magnitude of tooth displacement and Von Mises Stress of PDL,mandible and tooth roots were analyzed.Results: 1.Successfully established three-dimensional finite element models of the mandibular anterior region with reduced alveolar bone height and different positions of lingual fixed retainers.2.Tooth displacement: tooth mobility increased progressively with the degree of alveolar bone horizontal resorption.Wearing a lingual fixed retainer significantly reduced tooth mobility of the lower incisor teeth,and tooth movement was minimized when the lingual fixed retainer was located in the incisal 1/3.However,the mobility of canine teeth slightly increased.3.The Von Mises Stress distribution of PDL:The stress in the PDL was highest at the cervical margin,with the max stress being central incisors > lateral incisors > canines.Stress concentration areas were prone to occur at the labial and lingual cervical margins.Stress gradually decreased from the cervical margin to the middle,but increased in the apical 1/3 area.As the alveolar bone height decreased,PDL stress increased significantly,as did the stress in the stress concentration areas.Wearing a lingual fixed retainer could lower the maximum stress in the PDL,with the most significant stress reduction when the retainer was located in the incisal 1/3.4.The Von Mises Stress distribution of alveolar bone: In all models,the stress was higher near the cervical margin on the labial and lingual sides of the alveolar fossa,decreasing downwards,with the maximum stress in central incisors > lateral incisors > canines.The maximum stress in the alveolar bone increased as the alveolar bone decreased,but wearing a lingual fixed retainer could lower this stress,with the most significant stress reduction when the retainer was located in the incisal 1/3.5.The Von Mises Stress distribution in the root:Wearing a lingual fixed retainer could reduce the stress in the apical stress concentration area,with the greatest reduction when the retainer was located in the incisal 1/3..Conclusions: 1.Under occlusal force loading,tooth mobility,Von Mises Stresses in PDL and alveolar fossa steadily increase with the degree of alveolar bone horizontal resorption.2.Under occlusal force loading,wearing a lingual fixed retainer considerably reduces the overall motility of the lower anterior teeth,resulting in a more uniform distribution of tooth motility and periodontal tissue Von Mises Stresses.3.The optimal position for the retainer appears to be the incisal third of the tooth,yielding the lowest overall tooth mobility and most uniform Von Mises Stress distribution in periodontal tissues.