Study On Biomechanical Characteristics Of Different Loading Methods In The Closure Of The Extraction GAP In A Personalized Lingual Appliance

Background and objectives:In recent years,the development and application of digital technology in the field of oral cavity has made great progress in orthodontics and greatly promoted the development of digital aesthetic orthodontics.Representative of them--personalized tongue correction device,has the advantages of determining the therapeutic effect,wide indications,difficult malocclusion cases are also applicable,and can achieve the"perfect invisible"effect,favored by more and more patients and orthodontists.However,personalized lingual correction technology is also different from the traditional labial correction technology.The study on its biomechanical mechanism is not complete,and the therapeutic effect is still difficult to predict.Liu dawei et al.analyzed the biomechanical mechanism of closing the tooth extraction gap stage of the lingual correction system by sliding method by establishing a 3d finite element overall model containing teeth,periodontal membrane,alveolar bone and lingual correction bracket system,and simulated the closure of the tooth extraction gap by individual palatal force in clinical personalized lingual correction.The study found that with the increase of palatal side loading force value,tooth column appeared above the jaw in first molars width increases,the second molars and reverse horizontal arch effect,and the first molar teeth lingual inclination elongation,before fa r elongation and second molars in whole elongation as the main characteristics of the vertical direction of the"arch effect"^[1].For the maxillary anterior teeth,the lingual pallet is further away from the center of impedance in the vertical direction,so when the horizontal adduction is applied,the anterior teeth are more likely to slant toward the tongue.These problems are unfavorable to the final results of personalized lingual correction.How to better control the stability of tooth movement in adjunctive therapy is the key and difficult point of personalized lingual correction.In this study,a three-dimensional finite element model of personalized lingual correction was established to analyze the influence of different buccal and palatal loading modes and different lengths of traction hooks on the distribution of periodontal membrane stress and the overall tooth movement trend in the stage of personalized lingual correction with tooth extraction clearance closed.Methods:A healthy adult volunteer was selected to establish a three dimensional finite element model,.Four kinds of loading methods were simulated respectively,group A:Palatal side1.5 N,group B:buccal side 0.5 N+Palatal side 1N,group C:buccal side1.0N+Palatal side 0.5N,group D:buccal side 0.75 N+Palatal side 0.75N respectively,Combined with 2mm,3mm,4mm,5mm length traction hook respectively,16 groups of working conditions were established.The effects of different loading modes and different length of traction hook on the stress distribution and tooth movement trend of periodontal ligament were analyzed and compared.Results:The stress values of periodontal ligament in group A were higher than those in the other three groups.Inthe other three groups,the maximum stress value of periodontal membrane decreased with the increase of traction hook.Except for group A,the displacement values of X axis in the other three groups decreased gradually with the increase of the traction hook,and the tongue inclination was improved.In the buccal palatal side of the three groups at the same time,horizontal and vertical direction of the"arch effect"trend significantly improved.Conclusion:the application of buccal and palatine force and the extension of traction hook in closing the extraction space of the lingual correction system can reduce the stress level of periodontal membrane and effectively improve the lingual inclination of the anterior teeth,which is beneficial to the overall movement of the teeth.