Abstract: Objective To analyze the structure around the mini-implants between maxillary second premolar and first molar or mandibularsecond molar with Cone-beam computed tomography (CBCT) for the clinical plantation of mini-implants. Methods A total of 34 subjects were selected from patients who had undergone CBCT examinations.The distance between the simulative mini-implants and the occlusal plane and the thickness of maxillary infrazygomatic crest at different insertion angles were measured.The smallest angle and the thickness ofbuccal alveolar bone of the simulative mini-implants in different insertion heights were measured in the mandible. Results ① When the insertion angle was 40° to 75°,the thickness of the infrazygomatic crest was (4.7±0.3)～(8.0±0.1)mm,13～17 mm from the maxillary occlusal plane.②In different insertion cases,the insertion angle should be greater than 82°,11 mm from the mandibular occlusal plane.The buccal alveolar bone of the mandibular second molar was the thinnest.While the distance was 16 mm,the insertion angle should be greater than 51° and the buccal alveolar bone was the thickest.③ The distance to the mandibular tube was the shortest((9 ± 1.6)mm) when the insertion site was 16 mm from the occlusal plane among different insertion sites. Conclusions ①To ensure that the thickness of the infrazygomatic crest was greater than 6 mm and not touching the inferior wall of the maxillary sinus,the ideal insertion site was 13～16 mm from the maxillary occlusal planeat the angle of 55° to 75°.② When the insertion site was buccal to the mandibular second molar,the distance of mini-inplant to the occlusal plane should be greater than 12 mm.The smallest insertion angle variedfrom the insertion sites.

Key words: mini-implants, CBCT, infrazygomatic crest, maxillary sinus, mandibular canal