Research Of Using Cone Beam CT About The Safe Region Of Orthodontic Micro-implant Used For Anchorage Positioning In Maxillary Posterior Alveolar Bone

Objective: This study aims to use cone-beam CT (CBCT) to determine themesiodistal distance between the adjacent roots of maxillary posterior teeth,and thevertical distance from maxillary sinus bottom to the horizontal plane, combining withthe crown height measurements of bilateral maxillary posterior teeth in extra-oralmaxillary model and the measurements of attached gingiva width about bilateralmaxillary posterior teeth in the mouth.These measurements are all used for analyzingto determine the safe region of orthodontic micro-implant used for anchorage, in orderto offer orthodontists some useful reference.Methods: Choose clinic craniofacial bone CBCT data of21pre-orthodontic casesfrom January2012to December2012in General Hospital of Shenyang Military DentalClinic, including8cases of male patients medical records and clinical data of13casesof female patients, the age range of these cases is15-30years, mean age is (19.5±4.6)years.Using KaVo3D exam Vision Imaging System which produced in Germanycomposed with the scanner and computer workstations to obtain the cone-beam CTimages of patients about head and neck and the data reconstruction.Thereconstruction results use the format of DICOM3.0and save the output. Use InvivoDental5.0three-dimensional cephalometric analysis software to present the reconstructed data in the form of three-dimensional images, and determine horizontal,sagittal and coronal plane in Scetion window at Invivo Dental5.0software. Then usethe measurement function that comes with the software to measure both sides of themesiodistal distance of two adjacent teeth in posterior maxillary alveolar bone at6,8,10,12,14,16mm from the horizontal plane,and the vertical distance from the lowestpoint of maxillary sinus to the horizontal plane. Meanwhile, use vernier caliper tomeasure posterior maxillary teeth crown height in the plaster maxillary dentitionmodel,and use periodontal probe along the long axis of the tooth in mouth to measurethe width of free gingival and the width from gingival margin to mucogingivaljunction, thus we can obtain the attached gingiva width. Analyzing comprehensivelyall the measurements and the relationship between relevant anatomical structures, andfinally we can get the safe region of orthodontic micro-implant used for anchoragepositioning in maxillary posterior alveolar bone.Results:1.The measurements of mesiodistal distance about two adjacent toothroots in posterior maxillary alveolar bone show: the mesiodistal distance of themaxillary second premolar and mesiobuccal root of the maxillary first molar is thewidest, the mesiodistal distance of maxillary first premolar and maxillary secondpremolar is wider, and the mesiodistal distance about distobuccal root of maxillaryfirst molar and mesiobuccal root of maxillary second molar has large variation.2.Themeasurements of the vertical distance from the lowest point of maxillary sinus to thehorizontal plane show: the height is gradually reduced from the maxillary firstpremolar to the maxillary second molar, and in the maxillary second molar the heightis the lowest.3. The maxillary tooth crown height measurement results show: fromthe maxillary first premolar to the maxillary second molar, the tooth crown heightgradually decreases, the maxillary first premolar crown height is the highest.4.Thefinal results of the width of the posterior maxillary attached gingiva show: the widthof attached gingiva from the maxillary first premolar to the maxillary second molargradually increases, and the maxillary second molar region has the widest attachedgingiva. Conclusion: The safe region of orthodontic micro-implant used for anchoragepositioning in maxillary posterior alveolar bone is between the maxillary secondpermolar and the maxillary first molar, at10-11mm vertical distance from thehorizontal plane which determined by the ligature of the buccal cusp of maxillarysecond premolar and mesiobuccal cusp of maxillary first molar, by the tangency oftwo teeth adjacent contacts in the distal side and implantation angle of themicro-implant with the horizontal plane is no more than59°.