Effect Of A Digital Guide On The Positional Accuracy Of Intermaxillary Fixation Screw Implantation In Orthognathic Surgery

Background:1.Intermaxillary fixation screw(IMFS)implantation is a common procedure in orthognathic surgery performed to the temporary maxillary-mandibular fixation and stable bite relationships.The aim of this study was to assess the accuracy of IMFS implantation with a digital guide to reduce the occurrence of root damage.2.To evaluate the effect of IMFS tilt angle on root proximity and on the stress distribution of root and periodontal ligament,and to provide the perspective reference for safe implantation of IMFS in countries and regions that unconditionally design and manufacture digital guide plates.Methods:This prospective study involved 40 patients undergoing orthognathic surgery at the Affiliated Hospital of Qingdao University,from August 2017 to February 2023.The patients were randomly divided into two groups according to whether the IMFS implantation with or without digital guide(20 patients in the experimental group and 20 controls).The digital guides used in the experimental group were designed according to a virtual implantation plan and printed using stereolithography.In the control group,IMFSs were directly implanted by a surgeon based on clinical experience.Postoperatively,cone-beam computed tomography was performed to compare root proximity of IMFSs between the two groups,and the accuracy of IMFS placement was verified.The horizontal inclination angle of the IMFS and root proximity were measured in the control group and the correlation was analyzed and compared.At the same time,the preoperative CBCT imaging data of one patient in the above study were selected to establish a three-dimensional finite element model containing dentition,periodontal ligament,jaw and IMFS.The mini-screw was inserted perpendicular to the surface of the bone of specific locations,and then tilted the IMFS by 10 degrees and 20 degrees to the mesial and distal teeth respectively and analyzed the stress distribution of the periodontal tissue of the adjacent teeth after the IMFS implanted with different angles.Results:1.In the experimental group,there was no case of root damage,the incidence of the periodontal ligament(PDL)injured was 22.1%;and 77.9%IMFSs were placed without contacting adjacent anatomic structures.In the control group,the incidence of root damage had been up to 20.8%,and 31.7%IMFSs injured the PDL;only 47.5%IMFSs were placed between the roots(P<0.001).2.The IMFS horizontal inclinations ranged from 83° to 98°,and the correlation coefficients between root proximity and horizontal inclination were 0.148 and-0.181 respectively(P>0.05).3.When the VMFS tilted from the vertical alveolar bone to the distal adjacent teeth,the stress of the adjacent mesial roots gradually increased and was significantly higher than that of the distal roots.On the contrary,when the IMFS lean from the vertical bone to the mesial teeth,the stress of the distal roots gradually increased.The stress variation trend of the PDL was like that of the root stress.The stress of the adjacent tooth root and PDL was the most homogeneous,when the IMFS was impalanted vertically.And it would change remarkablely,when the axis of IMFS was tilted 10-degree and 20-degree from the point of vertical insertion,resulting in stress concentration.Conclusion:This study confirmed that IMFS could be placed more accurately with digital guides,reducing the incidence of root and periodontal ligament damage,which was better than that without the digital guide.The degree of horizontal tilt of IMFS was closely related to the root proximity,and the more inclination,the smaller the root proximity.It was recommended to insert the IMFS as vertical as possible into the alveolar bone surface to avoid root damage resulting by excessive stress,which was a clinically ideal implantation angle in the area without digital guide.