Three-dimensional Finite Element Analysis Of Maxillary Molar Distalization With Miniscrew Anchorage

Objective This study aimed to establish a three-dimensional finite element model composed of the maxillary teeth,periodontal ligament,alveolar process,straight wire appliance,and buccal interradicular miniscrew implants,and analyze the mechanical characteristics of three conditions of maxillary molar distalization supported by minscrew implants,including(1)distalizing the second molar alone,(2)distalizing the first and second molars together,and(3)distalizing the entire maxillary arch en masse,and to provide biomechanics reference for maxillary molar distalization in clinical orthodontics treatment.Methods Computed tomography(CT)images of the maxillary teeth and alveolar process were created by cone beam CT(CBCT)scanning.A three-dimensional finite element model was constructed to simulate the maxillary teeth,periodontal ligament,alveolar process,straight wire appliance,and interradicular miniscrew implants,by using a series of computer aided design(CAD)software and finite element analysis software.Then simulate the three conditions of maxillary molar distalization in the finite element analysis software:(1)To simulate distalizing the second molar alone,2.5N was loaded to simulate the thrust created by Ni-Ti spring between the first and second molar.The hook and the miniscrew implant was fixed joint.(2)To simulate distalizing the first and second molars together,2.5N was loaded to simulate the thrust created by Ni-Ti spring between the second premolar and the first molar.The hook and the miniscrew implant was fixed joint.(3)To simulate distalizing the entire maxillary arch en masse,2.5N was loaded between the hook and the miniscrew implant.The displacement of each tooth and the von Mises stress distribution of the periodontal ligament was calculated by the finite element analysis software three-dimensionally.Results A high precise three-dimensional finite element model was established to simulate the maxillary molar distalization supported by interradicular miniscrew implants.The calculation results indicated that:(1)When distalizing the second molar alone,the second molar demonstrated apparently sagittal distalization and distal tripping,buccal tripping and mesial-out rotation,and distal intrusion,and the anchorage effect in the anterior segment worked well;(2)When distalizing the first and second molar together,the molars both demonstrated sagittal distalization and distal tripping,buccal tripping and mesial-out rotation,and distal intrusion,but with smaller inclination and displacement,and weaker anchorage effect in the anterior segment;(3)When distalizing the entire maxillary arch en masse,the force lead to slight expansion of the maxillary arch,apparent lingual inclination in the anterior segment,small amounts of distal tripping in the posterior teeth,and obvious intrusion of the incisors,while the distalization displacement decreased from the central incisor to the second molar.The maximum of the periodontal ligament von Mises stress of the above three conditions was 18 k Pa,14 k Pa,and 4k Pa.Conclusion In the molar distalization system aied by buccal interradicular miniscrew implants,(1)the displacement patterns and the periodontal ligament stress distribution in the maxillary arch affected by the different ways of molar distalization;(2)under the same distalization forces,more sagittal distalization displacement was found in one molar distalization rather than two molar together,and the anchorage effect in the anterior segment seemed better in the former,however,more inclination also existed there;(3)the torque of the anterior segment should be especially controlled in distalizing the entire maxillary arch en masse,for the possibility of apparent lingual inclination in the anterior segment.