Three-dimensional Analysis Of Molar Distalization By Using Removable Clear Appliance Combined With Micro-implant Anchorage

The rapid development of computer technology and three-dimensional reconstruction technology makes it popular in the field of orthodontics,resulting in the generation of removable clear appliance.The clear aligner becomes favorite with more and more adults because of its aesthetic,comfortable and clean advantages.In orthodontic treatment,molar distalization is a main measure to correct class ? malocclusion without teeth extraction.The clear aligner is as well widely used in molar distalization because of its especial mechanical system.However,due to the limitation of thermoplastic material,anchorage loss of anterior teeth may come along with molar distalization.The objective of this research is to evaluate the efficiency and three-dimensional characteristics of molar distalization by using removable clear appliance combined with micro-implant anchorage,in order to supply theoretical basis for design and clinical application of clear aligner.Objective:1.Discuss the influence of micro-implant anchorage on efficiency of molar distalization by staged digital model surperimposition.Explore the changing of efficiency of maxillary second molars on different treatment stages.Discuss whether a difference of efficiency existed between the first molars and the second molars.2.Discuss the three-dimensional characteristics of molar distalization by using removable clear appliance.3.Analyze the effect of micro-implant anchorage on anchorage reinforcement of anterior teeth.Methods:Part 1: Choose 15 adult patients with clear aligners,8 of them combined with micro-implant anchorage and 7 of them without micro-implant anchorage.Observational teeth consist of 30 maxillary first molars,30 maxillary second molars and 40 maxillary premolars.Initial and staged plaster molels were obtained and laser-scanned every ten pair of aligner.Calculate the distalization efficiency of teeth and staged efficiency of second molars in different treatment stages and the difference of efficiency of maxillary first and second molars by using digital model superimposition.Contrast that they have or not statistic difference between them.Part 2: Choose 12 patients on the basis of part one,consist of 24 maxillary first molars,24 maxillary second molars and 28 maxillary premolars totally.Calculate the position changes of molars in buccolingual and axial direction,as well as the changes of rotation.Contrast that they have or not statistic difference between them.Part 3: Choose 15 models on their twentieth aligner from part one,consist of 16 maxillary central incisors combined with micro-implant anchorage and 14 maxillary central incisors without micro-implant anchorage totally.Calculate the position changes of central incisors in sagittal and horizontal direction.Contrast that they have or not statistic difference between them.Result:1.No statistic difference was found between two groups on efficiency of second molars,first molars and premolars(P?0.05).Statistic difference was found between efficiency of second molars and first molars regardless of micro-implant anchorage(P?0.05).The difference of efficiency of second molars between the tenth stage and the twentieth stage has statistical significant when combined with micro-implant anchorage(P?0.05).2.No statistic difference was found between the second molars and the first molars in buccolingual direction as well in axial direction(P?0.05).No statistic difference was found about rotation change in the second molars as well as in the first molars(P?0.05).The changes of rotation of premolars has statistical significant(P?0.05).3.No statistic difference of central incisors was found between two groups in sagittal and horizontal direction(P?0.05).Conclusion:1.Upper molar distalization can be achieved effectively by removable clear appliance.The efficiency of molar distalization will be increased slightly but there is not statistic difference when combined with micro-implant anchorage.The efficiency of maxillary second molars will decrease along with the distal movement of follow-up teeth.2.Slight intrusion and buccal displacement existed during molar distalization.Buccolingual rotations were easily to happen in premolars during distalization.3.Anchorage loss of incisors can be decreased slightly when combined with micro-implant anchorage,pulling with canines.However,this traction mode is still difficult to achieve the ideal anchorage reinforcement.