Study Of The New Fixed Occlusal Splint Appliance Combined With Miniscrew Anchorage For Molar Intrusion

Objectives: The biomechanical effects of the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion were studied by 3D finite element analysis.Through the clinical application of this method,the 3D dentition model and CBCT before and after the treatment were analyzed,and the curative effect and safety of the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion were evaluated,providing a theoretical basis for its clinical application and promotion.Methods: Part 1: In clinical practice,CBCT scan data of a 35-year-old female patient with complete maxillary dentition,unilateral first molar,and second molar need to intrude at the same time,good dental adjacency and periodontal health were selected.Mimics,Geomagic,and 3-matic software were applied to build and deal with the new fixed occlusal splint appliance and the corresponding dentition,periodontal membrane,alveolar bone,and miniscrew 3D model,using Abaqus finite element analysis software,under the different conditions of whether there was miniscrew anchorage combined with molar intrusion,the stress distribution of overerupted molars and anchorage teeth,the maximum von Mises stress of periodontal membrane at each tooth position and the displacement trend of anchorage teeth were compared.Part 2: 12 Stomatological Hospital Affiliated with Kunming Medical University from 2020-2023,due to molar loss,maxillary molar overerupted was required to be intruded for subsequent repair treatment were selected.Using the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion.A total of 49 molar teeth were measured,including 19 molar teeth(7 maxillary first molar,12 maxillary second molar)and 2 mesial anchorage adjacent teeth.The control group included a total of 15 antimaxillary healthy molars that had not been treated in the sample population.3D digital models and CBCT images of dentition before and after orthodontic treatment were obtained.Model overlap and CBCT analysis were performed to study the changes of crown displacement in 3D direction,root length,and alveolar bone height before and after treatment of overerupted molars and adjacent anchorage teeth,and statistical analysis was conducted.Results:Part 1: 3D finite element analysis of the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion1.The 3D finite element model of the new fixed occlusal splint appliance for molar intrusion(Model 1)and the 3D finite element model of the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion(Model 2)were established.The established model can reflect the situation of two different anchorage systems realistically and is highly similar to the clinical application,and the results have good credibility.2.The new fixed occlusal splint appliance can effectively disperse the reaction force of the intruded molar to each tooth position.After the combination with miniscrew anchorage,the stress distribution,the maximum von Mises stress value of the periodontal membrane,and the displacement trend of the overerupted molars were not significantly different due to the same intrusive force along the long axial root of the teeth.The stress on the anchorage teeth is significantly reduced,the displacement trend is significantly decreased,and the maximum von Mises stress of the periodontal membrane at each anchorage tooth position is significantly decreased.The maximum von Mises stress of the periodontal membrane of the adjacent second premolar decreased from 0.07537 Mpa to 0.01135 Mpa,and the maximum von Mises stress of the periodontal membrane of the first premolar decreased from0.04305 Mpa to 0.00751 Mpa.3.The new fixed occlusal splint appliance intruding molars,the movement of anchorage teeth generally shows a rotation trend.The adjacent premolar and the cusp are overerupted and mesial tilts,and the incisor tilts to the lip and intruded.The displacement of the posterior teeth on the opposite side was small,and the displacement after the combined miniscrew anchorage was not significant.Part 2:The clinical study of the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion1.After the new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion about(5.56±0.82)months,the intrusion of the first and second molar were(2.16±0.40)mm and(1.94±0.39)mm(P<0.05).Compared with the control group,there was no statistical significance in the horizontal and sagittal movement of overerupted molars,and there was no statistical significance in the three-dimensional movement of adjacent anchorage teeth.2.There is a small amount of absorption in the root of the overerupted tooth after intrusion.The change of mesial buccal root length was(-0.49±0.10)mm,the change of distal buccal root length was(-0.43±0.09)mm,and the change of palatine root length was(-0.44±0.10)mm(P<0.05).There was no statistical significance in root length of anchorage adjacent teeth and alveolar bone height of anchorage adjacent teeth and overerupted molars compared with the control group.Conclusions:1.After the miniscrew anchorage was included in the molar intrusion with the new fixed occlusal splint appliance,the stress distribution and displacement trend of the overerupted molar had no significant change due to the same stress condition,while the stress distribution and displacement trend of the anchorage molar significantly decreased.Miniscrew anchorage can significantly reduce the force of anchorage teeth,and avoid the movement of anchorage teeth,to a better expression of orthodontic force and improve the efficiency of orthodontic treatment.2.The new fixed occlusal splint appliance combined with miniscrew anchorage for molar intrusion has a stable and stable orthodontic force,which can effectively achieve the overall molar intrusion,limit the movement of anchorage teeth in the direction,and not cause root resorption of anchorage teeth and the reduction of alveolar bone height at each tooth position.After overerupted molar intruded,the tooth root absorption was small.3.The new fixed occlusal splint appliance is fixative and connected with the anchorage dentition to unite the anchorage teeth as a whole.With the miniscrew anchorage,most of the reaction force can be transmitted to the jaw,and the remaining reaction force can be dispersed to multiple teeth through the appliance,realizing the mixed anchorage of teeth and miniscrew.Moreover,in this method,the implantation site of the miniscrew is flexible,and a single miniscrew can intrude unilateral double molars,providing a new solution for difficult cases of clinical molar intrusion.At the same time,the appliance is transparent,beautiful,comfortable,simple to make,and can be popularized in clinical applications.