| Background:Mini-implant,as an “absolute anchorage”,not only simplifies the orthodontic procedure,but also offers new possibilities for orthodontic treatment.According to the literatures,the success rate of mini-implant ranges from 70% to 90%.Many factors can affect the success rate of mini-implants.And root damage was widely thought to be the major factor.Because the orthodontists always determine the insertion angle according to their experience,and the root orientation and interradicular distance cannot be judged accurately,leading to root damage and loosening or loss of mini-implants.Threedimensional guided insertion can realize the precise control of mini-implant insertion site and angle,and then promote the success rate of mini-implant.However,the current surgical guides at home and abroad are only suitable for the placement of buccal and palatal interradicular mini-implants,but cannot be used to guide the placement of infrazygomatic mini-implants.The reason is that the infrazygomatic mini-implant is inserted in a special way.It needs to be entered 1 mm perpendicular to the cortical bone at the start of placement,then rotate the screwdriver inferiorly to achieve a final insertion position buccal to the roots of molars.Therefore,it is urgent to fabricate a different surgical guide whose guide track can be adjusted.Objectives:To fabricate a two-trajectories surgical guide based on the bone quantity analysis of the IZC region,which conforms to the special implantation method of infrazygomatic mini-implant and allows clinicians to alter the insertion angle.It is hopeful to achieve precise implantation of mini-implants in the IZC region and improve the success rate.Contents:1.Bone quantity analysis of the IZC region.2.Development of the surgical guide for infrazygomatic mini-implant placement.3.A historical control study on the success rate of infrazygomatic mini-implant placement under the guidance of the surgical template.Materials and Methods:1.The CBCT of 111 patients before orthodontic treatment was randomly selected,and the measurement was conducted in Dolphin software.The buccal alveolar bone thickness,interradicular distance and buccal bone height were analyzed in 3 regions of 111subjects: between the second premolar and first molar(U56),between the mesiodistal roots of the first molar(U6),and between the first and second molars(U67).2.Patients requiring infrazygomatic mini-implant placement between the upper first and second molars were collected from June 2021.CBCT and intraoral scanning images of them were acquired and integrated into a 3D integrated maxillodental model containing soft and hard tissues in Geomagic Wrap software.Additionally,mini-implant placement simulation was conducted in Mimics software.The design of the surgical guide for infrazygomatic mini-implant insertion was then performed in 3 Shape Dental Manager and Geomagic Wrap software.Finally,the acrylic template was duplicated in Sprint Ray 3D printing printer.3.Patients who visited the Third Affiliated Hospital of Air Force Medical University from January 2016 to August 2022 and needed mini-implant insertion in the IZC region were selected.The surgical guide group consisted of 13 patients and the historical control group consisted of 27 patients.In the surgical guide group,mini-implant placement was performed using the surgical guide.In the historical control group,the cases were reviewed and the data was collected.All implantation operations were performed by the same doctor.And the success rate of mini-implant placement in two groups was statistically analyzed.Results:1.Results of Experiment 1: The thickest buccal alveolar bone in the IZC region was observed at 7 mm from the alveolar crest between the first and second molars;the buccal interradicular distance had a maximum at 11 mm from the alveolar crest between the second premolar and the first molar;the buccal alveolar bone height was not statistically different in each region,but there were great individual differences in the anatomical position of the maxillary sinus;the buccal alveolar bone thickness and interradicular distance were greater in males than in females;the buccal alveolar bone thickness was greater in adolescents than in adults,while the interradicular distance was greater in adults than in adolescents.2.Results of Experiment 2: The surgical guide included a retention part and a guide part,the retention part covered 3 teeth,and an outer guide part and a movably inner guide tube composed the entire guide part.The diameter of the inner guide tube was the same as the end diameter of the screwdriver.Additionally,two push rods were set symmetrically on the side wall of the inner guide tube.Commensurately,there are two L-shaped slideways on the side wall of the outer guide part.Therefore,the inner guide tube could move within the outer guide part and the guided trajectory transformation could be achieved during the infrazygomatic mini-implant placement procedure.A deviation of(1.23±0.78)mm and(1.29±0.57)mm at the mini-implant apex and crown was indicated,and the angular deviation was(5.41±3.61)°.3.Results of Experiment 3: In the surgical guide group,26 mini-implants were placed in the IZC region under the guidance of the two-trajectories surgical guide,and the success rate was 100%.The success rate was 79.6% in the historical control group,and there was statistically significant difference between the two groups.Conclusion:1.The optimal site for infrazygomatic mini-implant placement is between the upper first and second molars,and the diameter of the selected mini-implant cannot exceed 2mm;the buccal alveolar bone thickness and interradicular distance are greater in males than in females,suggesting that evaluation of the bone condition is more necessary in female patients before placing a mini-implant;the buccal bone thickness is greater in adolescents than in adults,while the buccal interradicular distance in adults is greater than in adolescents,indicating that adolescents are more suitable for a buccally placed miniimplant than adults.Especially for adolescents whose second molar has not erupted,infrazygomatic mini-implants can be placed buccally between the second premolar and first molar to prevent the second molar from injury.But the mini-implant with a smaller diameter such as 1.4 mm should be selected and a more parallel insertion angle to the molars’ root is needed.Considering the individual differences in the anatomic location of the maxillary sinus,preoperative CBCT should be taken to determine the optimal site of mini-implant placement and evaluate its safety.2.The two-trajectories surgical guide was in good retention,comfortable and with a high implantation accuracy.3.The two-trajectories surgical guides can enhance the success rate and stability of infrazygomatic mini-implants,and be further promoted in the clinical practice.However,further researches were needed due to the limited sample size. |
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