| Background:Maxillary protrusion is a common problem in face deformities,which seriously affects the patient’s appearance and psychology.The method of removing the two maxillary first premolars and retracting anterior teeth is often performed to treat the maxillary protrusion,The control of anchorage is especially important in order to maximize the retraction of anterior teeth.Compared with the traditional anchorage control methods,micro-implant anchorage has been widely used in clinic in recent years.The application of micro-screw implant anchorage to retract incisor is often accompanied by vertical problems such as lingual crown inclination and rotation of the occlusal plane.The change of occlusal plane will influence the occlusion,profile,the health of temporomandibular joint and the long-term stability of treatment.Vertical control of occlusal plane is the key point of orthodontic treatment for maxillary protrusion patients.Judging from the current study,scholars controlled the rotation of occlusal plane by torque control,bracket design,auxiliary arch,extraoral force and so on.The different position of micro-implant anchorage in retraction of anterior teeth will inevitably have different influence on the occlusal plane.The effects of microimplant anchorages in different positions on the occlusal plane,and whether the occlusal plane can be actively controlled by changing the position of the micro-implant anchorage need to be considered in clinic,but there is a few quantitative studies at present.Purpose:This study intends to establish a three-dimensional finite element model of the maxillary dentition of space closing by means of sliding mechanics to observe the initial displacement trend of the maxillary anterior and posterior teeth and the change law of the occlusal plane under the action of the anchorage of the micro-implant at different positions,and explore the influence of the change of the anchorage position of the micro-implant on the initial displacement trend of teeth and the rotation of the occlusal plane during this process,and explore its possible mechanical mechanism,in order to offer further support for the accurate control of teeth in clinical orthodontic treatment.Methods:A young male volunteer was selected as the data collection object,and the three-dimensional finite element model of the maxillary dentition,alveolar bone,and periodontal ligament was established through CBCT scanning data and using software Mimics 21.0 and Geomagic 2013.The software ANSYS Workbench 19.0 constructs three-dimensional models of traction hooks,maxillary arch wires,brackets,and micro-implant anchors in sequence and assembles them separately.The models are meshed,material properties and boundary conditions are set.According to the common clinical micro-implant anchorage design plan,the sagittal and vertical positions of the micro-implant anchorage were adjusted to set up 12 groups of models of closing the extraction space by sliding method under micro implant anchorage at different positions in the posterior tooth area,as well as 3 sets of models with depressive force at different positions in the anterior tooth area.Finally,the finite element method was used to calculate the force to observe and analyze the vertical displacement trend of the maxillary anterior and posterior teeth and the rotation trend of the occlusal plane under different working conditions.Results:Part I Establishment of FEM models according to adduction of upper anterior teeth through sliding mechanicsThe three-dimensional finite element model of closing the extraction space by sliding methods including maxillary bone,maxillary dentition,bracket,arch wire and micro-implant anchorage was established,with 878971 cells and 1304733 nodes in total.The overall grid quality of the model is high,the termination of relationship between all organizational structures is reasonable,and the biological similarity is high,which lays a good foundation for later data calculation and analysis.Part Ⅱ The influence of micro-implant anchorage position in molar area on occlusal plane when the maxillary anterior teeth are retractedThe change in the sagittal position of micro-implant anchorage mainly affects the horizontal displacement trend of anterior and posterior teeth.The clockwise rotation trend of occlusal plane increases with the distal movement of sagittal position of micro-implant anchorage;The change in the height of the micro-implant anchorage mainly affects the vertical displacement trend of anterior and posterior teeth.The counterclockwise rotation trend of occlusal plane increases with the increase of micro-implant anchorage height.Part Ⅲ The effect of anterior indentation force at different positions on occlusal plane when the maxillary anterior teeth are retractedAfter applying an indentation force in the anterior region,the pressure trend of the upper anterior teeth increases,the elongation trend of the molar increases,and the counterclockwise rotation trend of the occlusal plane increases accordingly.When the micro-implant anchorage is located between the central incisors in the anterior teeth area,the counterclockwise rotation trend of occlusal plane is the largest;When the micro-implant anchorage is located between the central incisor and the lateral incisor in the anterior teeth area,the force on the anterior periodontal ligament is more even than the other two methods,the anterior teeth are easier to achieve overall movement,and the rotation of the occlusal plane is minimal.Conclusions:1.The image data obtained by using CBCT scanning and relevant threedimensional finite element modeling software,can successfully establish the finite element model with high biological and geometric similarity,which can also be used for biomechanical mechanism research.2.Different positions of the micro-implant anchorage have different effects on the occlusal plane.The higher the micro-implant anchorage height is,the greater mesial movement the sagittal position of the micro-implant anchorage has,and the lower the clockwise rotation trend of the occlusal plane.3.Increasing the indentation force in the anterior teeth area can effectively control the occlusal plane,with more effective control of the vertical direction of the anterior and posterior teeth,making it easier to achieve the overall retraction of the anterior teeth.4.Different positions of the micro-implant anchorage will have different effects on the occlusal plane,suggesting that the vertical influence should be paid attention to when the maxillary anterior teeth are retracted in clinic.It can also be controlled vertically through the design of the anchorage position of the micro-implant. |
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